Nerve Block

Nerve Block (11)

Thứ tư, 22 Tháng 9 2010 19:56

Saphenous Nerve Block

Written by

Introduction

Clinicians in the emergency department and other acute care settings frequently encounter patients who have sustained trauma to the lower leg or foot and require anesthesia for repair.

Regional block of the saphenous nerve, a pure sensory nerve of the leg, allows for rapid anesthetization of the anteromedial lower extremity, including the medial malleolus. Regional blocks have several advantages compared with local infiltration, such as fewer injections required to attain adequate anesthesia, smaller volume of anesthetic required, and less distortion of the wound site. Because of the lower number of injections, this procedure is better tolerated by the patient and limits the chance of a needlestick injury to the provider.

The saphenous nerve block is gaining popularity not only for procedural anesthesia but also for treatment of pain after procedures. Recently, its use has been demonstrated to be an effective regional technique for post-meniscectomy pain.

While the saphenous nerve can be blocked above the knee, at the level of the knee, below the knee, or just above the medial malleolus, this nerve is commonly blocked at the ankle because of its predictable and superficial location.

Anatomy

Understanding the anatomical distribution of the saphenous nerve helps when performing a successful saphenous nerve block. The saphenous nerve is a cutaneous branch of the femoral nerve originating from the L2-L4 nerve roots. It descends anteroinferiorly through the femoral triangle, lateral to the femoral sheath, accompanying the femoral artery in the adductor canal, and then courses between the sartorius and gracilis muscles across the anterior thigh.

Descent of the saphenous nerve down the anteromedial aspect of the leg.

After piercing the deep fascia on the medial aspect of the knee, the nerve courses superficially down the anteromedial lower leg. The infrapatellar branches supply innervation to the knee. The saphenous nerve runs laterally alongside the saphenous vein, giving off a medial cutaneous nerve that supplies the skin of the anterior thigh and anteromedial leg. The saphenous nerve travels to the dorsum of the foot, medial malleolus, and the area of the head of the first metatarsal. At the level of ankle, the saphenous nerve is found between the medial malleolus and the anterior tibial tendon, just lateral to the saphenous vein.

Saphenous nerve dermatome of the anteromedial leg.

Saphenous nerve dermatome at the level of the foot.

Indications

  • Wound repair or exploration of the medial malleolus or anteromedial lower extremity
  • As part of an ankle block required to manipulate a fractured or dislocated ankle (A combination of posterior tibial, saphenous, superficial peroneal, deep peroneal, and sural nerve blocks results in complete block of sensory perception beneath the ankle.)

    Areas of anesthetization to complete an ankle block. This block requires anesthetization of 5 nerves for complete sensory block below the ankle. The areas to anesthetize include a line along the anterior ankle for the superficial peroneal nerve (blue line), the deep peroneal nerve (red star), the saphenous nerve (pink star), the sural nerve (green arrow), and the posterior tibial nerve (orange arrow).
  • Incision and drainage of an abscess in the medial malleolus or anteromedial lower extremity
  • Foreign body removal in the anteromedial lower extremity or medial malleolus
  • Pain after partial meniscectomy

Contraindications

  • Allergy to anesthetic solution or additives (eg, ester, amide)
  • Overlying cellulitis
  • Severe bleeding disorder or coagulopathy
  • Preexisting neurological damage
  • Patient uncooperativeness (Pediatric or elderly patients may need sedation.

Anesthesia

  • Lidocaine, the most commonly used anesthetic, has a fast onset of action and a duration of action of 30-120 minutes, which is increased to 60-400 minutes with the addition of epinephrine. The total cumulative dose of lidocaine to be infiltrated is 4.5-5 mg/kg (not to exceed 300 mg) if lidocaine without epinephrine is used, and 7 mg/kg (not to exceed 500 mg) if lidocaine with epinephrine is used.
  • Newer studies have shown that the addition of clonidine 100 mcg to 30 mL of 0.375% bupivacaine (with 5 mcg/mL epinephrine) significantly prolongs duration of the block. The use of clonidine is not yet well-studied, and the authors cannot recommend its use as standard of care at this time.
  • Topical anesthetics may be needed in children or uncooperative adults.

Equipment

  • Needle, 4 cm, 25 gauge (ga)
  • Needle, 18 ga
  • Syringe, 10 mL
  • Marking pen
  • Sterile gloves
  • Antiseptic solution (povidone [Betadine] or chlorhexidine gluconate [Hibiclens]) with skin swabs
  • Alcohol swabs
  • Sterile drape
  • Lidocaine 1%, 10 mL
  • Facial mask with eye shield
  • Sterile gauze

Positioning

  • Position the patient supine with the leg externally rotated and the ankle elevated (if anesthetizing at the level of the ankle) or knee elevated (if anesthetizing at the level of the knee).
  • Alternatively, the patient may sit and face the clinician.

Technique

Explain the procedure, benefits, risks, and complications to the patient and/or patient’s representative, and inform the patient of the possibility of paresthesia during the procedure.

Obtain informed consent in accordance with hospital protocol.

Perform and document neurovascular and musculoskeletal examinations prior to the procedure. Testing the saphenous nerve prior to block includes sensation of anteromedial thigh and lower leg.

Knee level

Expose the knee and palpate to identify the medial femoral condyle and the medial tibial condyle.

Identify the landmarks: medial femoral and tibial condyles.

Prepare the site with antiseptic solution. While maintaining sterile technique, place a skin wheal of local anesthetic using a 25-ga needle.

Antiseptic (Betadine) preparation.

Subcutaneously infiltrate 7-10 mL of local anesthetic solution in a transverse line from the posteromedial to the anteromedial aspect of either condyle.

Anesthetize posteromedial to anteromedial at either condyle.

If the leg does not need to be anesthetized, use the saphenous block technique for the level of the ankle.

Ankle level

Expose the area of injection and identify the landmarks. Start by palpating the medial malleolus and the great saphenous vein at the ankle. Mark the site 1.5 cm superior and anterior to the anterosuperior border of the medial malleolus.

Mark the site 1.5 cm superior and anterior to the medial malleolus.

Advance laterally in a transverse line toward the lateral malleolus to identify the anterior tibial tendon while the foot is in dorsiflexion (dorsiflexion exaggerates the tendon). Also identify the anterior tibial ridge by advancing further in the transverse line while the foot is in plantar flexion. A divot in the anterior ankle can be felt before the contribution by the fibula is met.

The divot between the anterior tibial tendon and the tibial ridge.

Prepare the site with antiseptic solution. While maintaining sterile technique, place a skin wheal of local anesthetic using a 25-ga needle.

Advance the needle through the skin wheal toward the anterior tibial tendon in a superficial transverse line, without injecting the tendon itself.

Saphenous nerve anesthetization site.

In some instances, further anesthesia is necessary (to the anterior tibial ridge) to get a complete block of the area.

Calor and rubor of the foot due to loss of sympathetic tone may initially be noted.

Pearls

  • Equipment preparation and proper patient positioning may make the difference between success and failure.
  • In children or noncompliant adults, consider using topical anesthetic mixtures, such as lidocaine, epinephrine, tetracaine (LET) or a eutectic mixture of lidocaine and prilocaine (EMLA cream).
  • Pediatric or elderly patients may require additional sedation for compliance.
  • Consider a hematoma block or bier block when a fracture exists or when more extensive manipulation of the foot is expected.
  • Adding a buffering solution, like sodium bicarbonate, can significantly decrease the pain of the injection when performing a nerve block. Add 1 mL of sodium bicarbonate (44 mEq/50 mL) to 9 mL of lidocaine.
  • Warming the anesthetic solution to body temperature can significantly decrease the pain of the injection.
  • When unassisted, tape a bottle of lidocaine upside down to the wall prior to the procedure. If more anesthetic is needed during the procedure, it can be obtained from this bottle without compromising the sterility of gloves and equipment.

Complications

  • Infection: Infection occurs when the puncture site is not clean. Avoid puncture through infected skin or skin lesions. Be sure to use sterile technique during the procedure, as the risk of infection is insignificant when sterility is properly maintained.
  • Intravascular injection: Intra-arterial injection may result in vasospasm and lead to ischemia of the limb tissue. Intravenous injection can lead to systemic toxicity when high doses of anesthesia are injected. Tissue texture changes revealing pallor, bogginess, and cool temperature may indicate that either intravascular injection or vascular compression has occurred. Always aspirate the syringe to rule out intravascular placement before injection. Alpha-adrenergic antagonists (eg, phentolamine 0.5-5 mg diluted 1:1 with saline) can be administered by local infiltration to relieve arterial vasospasm secondary to intra-arterial injection.
  • Nerve injury: Patients may develop paresthesia, sensory deficits, or motor deficits secondary to inflammation of the nerve. Most often, this type of neuritis is transient and resolves completely. During the procedure, pull back gently after induction of paresthesia so as to not inject the nerve directly. Make sure to document a complete neuromuscular examination both before and after the procedure.
  • Hemorrhage: Reports of significant hemorrhage during regional anesthesia are rare, even in patients with blood coagulopathies. A hematoma may develop with intravascular puncture. If prolonged bleeding occurs, attempt to obtain hemostasis with direct pressure and elevation.
  • Allergic reaction: Allergic reactions to local anesthetics occur at a rate of 1%. Reactions range from delayed hypersensitivity (Type IV) to anaphylactic (Type I). Although rare, the most common cause of allergic reaction to anesthetics is the preservative in the local anesthetic solution. Using cardiac lidocaine is an alternative, as it does not contain the preservative (eg, methylparaben). Alternatively, a 1-2% diphenhydramine solution can be used as a local anesthetic.
  • Exceeding total volume of anesthesia: The volume of 1% lidocaine without epinephrine should not exceed 5 mg/kg. If lidocaine with epinephrine is used, total volume should not exceed 7 mg/kg. Systemic toxicity manifests in the central nervous and cardiovascular systems. Signs such as tremors, convulsions, tachycardia, or respiratory compromise should alert the clinician to stop the procedure and reassess the patient.

Ultrasonographic Guidance

The use of ultrasound-guided techniques for regional anesthesia is becoming more popular. Ultrasonographic guidance is best for blocking the saphenous nerve when palpation of the saphenous vein is difficult. Despite tourniquet use or leg dependency, palpating the vein as a landmark may not be possible (eg, common in patients who are obese). In these situations, the use of ultrasonographic guidance is prudent. An additional advantage of this approach is to avoid puncturing the saphenous vein, especially at the level of the knee.

Paravenous approach at the level of the knee

  • This technique is well-described by Andrew Gray and Adam Collins.
  • A short-axis view of the saphenous vein is employed, with the needle directed nearly parallel to the transducer within the plane of imaging.
  • The approach begins at the level of the tibial tuberosity, with the needle entry site anterior to the aspect of the medial leg.
  • Using a high frequency linear probe, identify the saphenous vein and the fascia lata.
  • The goal is local anesthetic infiltration between these two landmarks on ultrasound.
  • A 25-gauge needle can then be directed in a posterolateral fashion to approach the nerve.

Adductor canal approach at the level of the knee

  • This approach is well-described by Jens Krombach and Andrew Gray.
  • Use a 14-MHz linear ultrasound transducer and scan the medial thigh 5-7 cm proximal to popliteal crease.
  • Slide the probe until the image of the adductor canal is obtained.
  • The saphenous nerve can be imaged where it pierces the membrane.
    • Recall that the saphenous nerve travels deep to the sartorius muscle adjacent to the descending branch of the femoral artery, which may be seen with power Doppler.
    • The saphenous nerve emerges between the sartorius and gracilis muscle tendons, piercing the fascia lata to join the saphenous vein within subcutaneous tissue.
  • Infiltrate 5-10 mL of local anesthetic adjacent to the saphenous nerve deep to the sartorius muscle.

Approach at the level of the ankle

Ultrasonographic guidance may also be employed at the ankle to identify the saphenous vein when it cannot be identified by visualization or palpation. This can serve as a starting point for identifying the landmarks (see Technique above). However, the saphenous nerve is usually not visible with ultrasound imaging at this level; therefore, the procedure typically relies on the landmarks.

A disadvantage of the ankle block is that it usually requires large volumes of local anesthetic. According to Frederickson, these volumes can be reduced with the use of ultrasonographic guidance because of the more precise needle placement and real-time repositioning that such guidance allows. This reference paper states that typical volumes of 30 mL can be reduced to 15 mL for the entire ankle block.

Four of the five nerves in the ankle block can be approached with an in-plane needle transducer orientation directly, using a vessel as a guide, except for the superficial peroneal nerve. These nerves and their corresponding vessels are as follows:

  • Deep peroneal nerve - Lateral to anterior tibial artery
  • Posterior tibial nerve - Posterior to posterior tibial artery
  • Saphenous nerve - Adjacent to the long saphenous vein
  • Sural nerve - Adjacent to the short saphenous vein

The saphenous nerve can be approached with a narrow curvilinear probe to allow a direct tangential needle approach. Please refer to Frederickson's paper, which diagrams this nicely.

Source Emedicine.medscape.com
Chủ nhật, 19 Tháng 9 2010 21:02

Superficial Peroneal Nerve Block

Written by

Introduction

Emergency practitioners and other clinicians working in acute care settings frequently encounter patients who have trauma to or pathology of the dorsum of the foot and require anesthesia for treatment and repair.

Regional block of the superficial peroneal nerve allows for rapid anesthetization of the dorsum of the foot, which allows for management of lacerations, fractures, nail bed injuries, or other pathology involving the dorsum of the foot. Regional blocks have several advantages compared to local infiltration, such as fewer injections required to attain adequate anesthesia, smaller volume of anesthetic required, and less distortion of the wound site. Because of the lower number of injections, this procedure is better tolerated by the patient and limits the chance of a needle stick injury to the provider.

This procedure, often overlooked in the emergency department, is safe, is relatively easy to perform, and can provide excellent anesthesia to the foot. In one study, regional anesthesia of the foot and ankle, when performed by surgeons, was completely successful 95% of the time.

Anatomy

Understanding the anatomical distribution of the superficial peroneal nerve is helpful in performing a successful blockade of this nerve. The superficial peroneal nerve arises from the common peroneal nerve, which also gives rise to the deep peroneal nerve. The superficial peroneal nerve originates between the peroneus longus muscle and the fibula. It courses down the lateral compartment of the lower leg along with the peroneus longus muscle and the peroneus brevis muscle. It then descends posterolaterally to the anterior crural intermuscular septum. It runs anterolateral to the fibula between the peroneal muscles and the extensor digitorum longus, eventually supplying the peroneal muscles.

In the distal third of the leg, it pierces the deep fascia to become superficial. The nerve splits into the medial dorsal cutaneous nerve and the intermediate dorsal cutaneous nerve, which give rise to the dorsal digital nerves. These nerves supply the skin of the anterolateral distal third of the leg, most of the dorsal foot, and the digits. However, this nerve does not supply the web space between the first and second digits or the lateral fifth digit. At the level of ankle, the superficial peroneal nerve splits to fan out between the medial and lateral malleoli.

Dermatome of the superficial peroneal nerve at the level of posterior calf.

Superficial peroneal nerve dermatome at the level of the anterior lower leg.

Indications

  • Wound repair or exploration of the dorsal regions of the foot
  • As part of an ankle block required to manipulate a fracture or dislocated ankle (A combination of posterior tibial, saphenous, superficial peroneal, deep peroneal, and sural nerve blocks results in complete block of sensory perception beneath the ankle. Compared with more proximal approaches to the ankle block, motor block is rarely a concern with the ankle block. 

Areas of anesthetization to complete an ankle block. This block requires anesthetization of 5 nerves for complete sensory block below the ankle. The areas to anesthetize include a line along the anterior ankle for the superficial peroneal nerve (blue line), the deep peroneal nerve (red star), the saphenous nerve (pink star), the sural nerve (green arrow), and the posterior tibial nerve (orange arrow).
  • Incision and drainage of an abscess in the dorsal regions of the foot
  • Removal of foreign body in the dorsal regions of the foot
  • Toenail repair (Toenail repair on the lateral first digit and medial second digit also requires deep peroneal nerve block.)
  • Symptomatic relief of compression of the common peroneal nerve (along with the deep peroneal nerve block)

Contraindications

  • Allergy to anesthetic solution or additives (eg, ester, amide)
  • Overlying cellulitis
  • Severe bleeding disorder or coagulopathy
  • Preexisting neurological damage
  • Patient uncooperativeness (Pediatric or elderly patients may need sedation.)

Anesthesia

  • Lidocaine, the most commonly used anesthetic, has a fast onset of action and a duration of action of 30-120 minutes, which is increased to 60-400 minutes with the addition of epinephrine. The total cumulative dose of lidocaine to be infiltrated is 4.5-5 mg/kg (not to exceed 300 mg) if lidocaine without epinephrine is used, and 7 mg/kg (not to exceed 500 mg) if lidocaine with epinephrine is used.
  • Topical anesthetics may be needed in children or uncooperative adults.

Equipment

  • Needle, 4 cm, 25 gauge (ga)
  • Needle, 18 ga
  • Syringe, 10 mL
  • Marking pen
  • Sterile gloves
  • Antiseptic solution (eg, povidone iodine [Betadine] or chlorhexidine gluconate [Hibiclens]) with skin swabs
  • Alcohol swabs
  • Sterile drape
  • Lidocaine 1%, 10 mL
  • Facial mask with eye shield
  • Sterile gauze

Positioning

  • Position the patient supine, with the ankle supported by a pillow or rolled sheet, optimizing comfort.
  • Alternatively, the patient may sit and face the physician while maintaining a similar leg elevation.

Technique

  • Explain the procedure, benefits, risks, and complications to the patient and/or patient’s representative, and inform the patient of the possibility of paresthesia during the procedure.
  • Obtain informed consent in accordance with hospital protocol.
  • Perform and document neurovascular and musculoskeletal examinations prior to the procedure. Testing the superficial peroneal nerve prior to performing the block includes the following:
  • Sensation of dorsum of the foot 

Superficial peroneal nerve dermatome at the level of the anterior lower leg.
  • Foot eversion
  • Expose the area of injection and identify the medial and lateral malleoli by palpation.
  • Draw a line from the distal anterior aspect of the lateral malleolus to the anterior border of the medial malleolus.

Line of anesthesia from lateral malleolus to medial malleolus.
  • Wipe the area with an alcohol pad and clean the site thoroughly with antiseptic solution, moving outward in a circular fashion.
  • Maintaining sterile technique, place an initial skin wheal of lidocaine anterior to the distal lateral malleolus using a 25-ga needle.
  • Insert the 25-ga needle through the skin wheal and infiltrate 6-10 mL in a transverse fashion until the medial malleolus is reached. 

Anesthetize along the line from lateral to medial malleolus.

Pearls

  • Equipment preparation and proper patient positioning may make the difference between success and failure.
  • In children or noncompliant adults, consider using topical anesthetic mixtures, such as lidocaine, epinephrine, tetracaine (LET) or a eutectic mixture of lidocaine and prilocaine (EMLA cream).
  • Pediatric or elderly patients may require additional sedation for compliance.
  • Consider a hematoma block or bier block to attain more effective analgesia when a fracture exists or when more extensive manipulation of the foot is expected.
  • Adding a buffering solution, like sodium bicarbonate, can significantly decrease the pain of the injection when performing a nerve block. Add 1 mL of sodium bicarbonate (44 mEq/50 mL) to 9 mL of lidocaine.
  • Warming the anesthetic solution to body temperature can significantly decrease the pain of the injection.
  • When unassisted, tape a bottle of lidocaine upside down to the wall prior to the procedure. If more anesthetic is needed during the procedure, it can be obtained from this bottle without compromising the sterility of gloves and equipment.

Complications

  • Infection: Infection occurs when the puncture site is not clean. Avoid puncture through infected skin or skin lesions. Be sure to use sterile technique during the procedure, as the risk of infection is insignificant when sterility is properly maintained.
  • Intravascular injection: Intra-arterial injection may result in vasospasm and lead to ischemia of the limb tissue. Intravenous injection can lead to systemic toxicity when high doses of anesthetic are injected. Tissue texture changes revealing pallor, bogginess, and cool temperature may indicate that either intravascular injection or vascular compression has occurred. Always aspirate the syringe to rule out intravascular placement before injection. Alpha-adrenergic antagonists (eg, phentolamine 0.5-5 mg diluted 1:1 with NaCl 0.9%) can be administered by local infiltration to relieve arterial vasospasm secondary to intra-arterial injection.
  • Nerve injury: Patients may develop paresthesia, sensory deficits, or motor deficits secondary to inflammation of the nerve. Most often, this type of neuritis is transient and resolves completely. During the procedure, pull back gently after induction of paresthesia so as to not inject the nerve directly. Make sure to document a complete neuromuscular examination both before and after the procedure.
  • Hemorrhage: Reports of significant hemorrhage during regional anesthesia are rare, even in patients who have blood coagulopathies. A hematoma may develop with intravascular puncture. If prolonged bleeding occurs, attempt to obtain hemostasis with direct pressure and elevation.
  • Allergic reaction: Allergic reactions to local anesthetics occur at a rate of 1%. Reactions range from delayed hypersensitivity (type IV) to anaphylactic (type I). Although rare, the most common cause of such an allergic reaction is the preservative (eg, methylparaben) in the local anesthetic solution. Preservative-free lidocaine (typically found in cardiac solutions) is an alternative, since it does not contain the preservative. Alternatively, a 1-2% diphenhydramine solution can be used as a local anesthetic.
  • Exceeding total dose of anesthesia: The dose of 1% lidocaine without epinephrine should not exceed 5 mg/kg. If lidocaine with epinephrine is used, total dose should not exceed 7 mg/kg. Systemic toxicity manifests in the central nervous and cardiovascular systems. Signs such as tremors, convulsions, tachycardia, or respiratory compromise should alert the physician to stop the procedure and reassess the patient.

Ultrasonographic Guidance

A disadvantage of the ankle block is that it usually requires large volumes of local anesthetic. According to Frederickson, these volumes can be reduced with the use of ultrasonographic guidance because of the more precise needle placement and real-time repositioning that such guidance allows. This refernce paper states that typical volumes of 30 mL can be reduced to 15 mL for the entire ankle block.

Four of the five nerves in the ankle block can be approached with an in-plane needle transducer orientation directly, using a vessel as a guide, except for the superficial peronieal nerve. These nerves and their corresponding vessels are as follows:

  • Deep peroneal nerve - Lateral to anterior tibial artery
  • Posterior tibial nerve - Posterior to posterior tibial artery
  • Saphenous nerve - Adjacent to the long saphenous vein
  • Sural nerve - Adjacent to the short saphenous vein

As noted by Frederickson, the superficial peroneal nerve is approaced in a traditional manner, as it does not travel with a vessel.

Source Emedicine.medscape.com
Thứ bảy, 18 Tháng 9 2010 11:33

Posterior Tibial Nerve Block - Technique

Written by

<< Posterior Tibial Nerve Block

Technique

  • Explain the procedure, benefits, risks, and complications to the patient and/or patient’s representative, and inform the patient of the possibility of paresthesia during the procedure.
  • Obtain informed consent in accordance with hospital protocol.
  • Perform and document neurovascular and musculoskeletal examinations prior to the procedure. Testing the posterior tibial nerve prior to block includes the following:
    • Sensation of sole of the foot, as shown below
  • Flexion, abduction, and adduction of the digits
  • Using nonsterile gloves, expose the area of injection and identify the landmarks, as depicted in the image below.

Posterior tibial nerve block landmarks. Medial malleolus (MM) is at the left and Achilles tendon is at right. Posterior tibial artery (A) is approximately 1 cm inferior to the site marked for needle insertion (arrow).
  • Start by palpating the medial malleolus and advance posteroinferiorly toward the Achilles tendon, as shown below, until the pulsation of the posterior tibial artery is felt.

Palpation of the posterior tibial artery.
  • Mark the point that is 0.5-1 cm superior to the posterior tibial artery, as shown below.

Marking the injection site, which is 0.5-1 cm superior to the posterior tibial artery.
  • If the artery is not palpable, mark a point 1 cm superior to the medial malleolus and slightly anterior to the Achilles tendon, as shown below.

Location of injection site when unable to palpate the posterior tibial artery.
  • Wipe the area with an alcohol pad, and clean site thoroughly with an antiseptic solution, moving outwards in a circular fashion, as depicted in the image below.
  • Open sterile drape and place the syringe, needle, and gauze on the tray, maintaining sterility.
  • Put on sterile gloves. Attach the 18-ga needle to the 10-mL syringe and draw up the lidocaine. Then, change to the 25-ga needle.
  • With the needle, place a skin wheal, as shown below, at the marked injection site. Advance the needle through the skin wheal toward the tibia at a 45° angle in a mediolateral plane, just posterior to the artery. Wiggle the needle slightly to induce paresthesia. If elicited, aspirate to make sure the needle is not in a vessel, wait for the paresthesia to resolve, and inject 3-5 mL.

Placing a skin wheal.
  • If paresthesia is not elicited, advance the needle at a 45-degree angle until it meets the posterior tibia. Withdraw 1 cm and inject 5-7 mL of anesthetic while withdrawing needle another 1 cm, as shown below.

Injection posterior and superior to the posterior tibial artery.
  • Calor and rubor of the foot due to loss of sympathetic tone may initially be noted.
  • Successful anesthesia of the areas noted heralds a successful posterior tibial nerve block.

Pearls

  • Equipment preparation and proper patient positioning may make the difference between success and failure.
  • In children or noncompliant adults, consider using topical anesthetic mixtures, such as lidocaine, epinephrine, tetracaine (LET) or a eutectic mixture of lidocaine and prilocaine (EMLA cream).
  • Pediatric or elderly patients may require additional sedation for compliance.
  • Consider a hematoma block or bier block when a fracture exists or when more extensive manipulation of the foot is expected to attain more effective analgesia.
  • Adding a buffering solution, like sodium bicarbonate, can significantly decrease the pain of the injection when performing a nerve block. Add 1 mL of sodium bicarbonate (44 mEq/50 mL) to 9 mL of lidocaine.
  • Warming the anesthetic solution to body temperature can significantly decrease the pain of the injection.
  • When unassisted, tape a bottle of lidocaine upside down to the wall prior to the procedure. If more anesthetic is needed during the procedure, it can be obtained from this bottle without compromising the sterility of gloves and equipment.

Complications

  • Infection: Infection occurs when the puncture site is not clean. Avoid puncture through infected skin or skin lesions. Be sure to use sterile technique during the procedure, as the risk of infection is insignificant when sterility is properly maintained.
  • Intravascular injection: Intra-arterial injection may result in vasospasm and lead to ischemia of the limb tissue. Intravenous injection can lead to systemic toxicity in high doses. Tissue texture changes revealing pallor, bogginess, and cool temperature may indicate that either intravascular injection or vascular compression has occurred. Always draw back the syringe to rule out intravascular placement before injection. Alpha-adrenergic antagonists (eg, phentolamine 0.5-5 mg diluted 1:1 with saline) can be administered by local infiltration to relieve arterial vasospasm secondary to intraarterial injection.
  • Nerve injury: Patients may develop paresthesia, sensory deficits, or motor deficits secondary to inflammation of the nerve. Most often, this type of neuritis is transient and resolves completely. During the procedure, pull back gently after induction of paresthesia so as to not inject the nerve directly. Make sure to document a complete neuromuscular examination both before and after the procedure.
  • Hemorrhage: Reports of significant hemorrhage during regional anesthesia are rare, even in patients with blood coagulopathies. A hematoma may develop with intravascular puncture. If prolonged bleeding occurs, attempt to obtain hemostasis with direct pressure and elevation.
  • Allergic reaction: Allergic reactions to local anesthetics occur at a rate of 1%. Reactions range from delayed hypersensitivity (type IV) to anaphylactic (type I). Although rare, the most common cause of allergic reaction is the preservative in the local anesthetic solution. Cardiac lidocaine is an alternative, as it does not contain the preservative. Alternatively, a 1-2% diphenhydramine solution can be used as a local anesthetic.
  • Exceeding total volume of anesthesia: The volume of 1% lidocaine without epinephrine should not exceed 5 mg/kg. If lidocaine with epinephrine is used, total volume should not exceed 7 mg/kg. Systemic toxicity manifests in the central nervous and cardiovascular systems. Signs such as tremors, convulsions, tachycardia, or respiratory compromise should alert the physician to stop the procedure and reassess the patient.
Source Emedicine.medscape.com
Thứ bảy, 18 Tháng 9 2010 11:23

Posterior Tibial Nerve Block

Written by

Introduction

Pratitioners in the emergency department frequently encounter patients who have sustained trauma to the sole of the foot and require anesthesia for repair. This tender area is relatively difficult to anesthetize locally. Regional block of the posterior tibial nerve allows for rapid anesthetization of the heel and plantar regions of the foot. Regional blocks have several advantages compared to local infiltration, such as fewer injections necessary to attain adequate anesthesia, smaller volume of anesthetic required, and less distortion of the wound site. Because of the lower number of injections, this procedure is better tolerated by the patient and limits the chance of a needle stick to the provider.

This procedure, often overlooked in the emergency department, is safe, relatively easy to perform and can provide excellent anesthesia to the foot. In one study, regional anesthesia of the foot and ankle, when performed by surgeons, was completely successful 95% of the time.

Anatomy

Understanding the arborization of the tibial nerve is crucial to a successful posterior tibial nerve block. The posterior tibial nerve arises from the sciatic nerve and courses down the posterior thigh and posteromedial lower leg, as shown below.

The tibialis posterior tendon, flexor digitorum tendon, posterior tibial artery, posterior tibial nerve, and flexor hallucis longus tendon at the ankle level.

These nerves supply the intrinsic muscles of the foot, excluding the extensor digitorum brevis. They also supply sensory innervation to the plantar surface of the foot, shown below. 

Cutaneous innervation by the medial and lateral branches of the posterior tibial nerve.

At the level of ankle, the posterior tibial nerve can be found midway between the medial malleolus and the heel. The nerve lies beneath the flexor retinaculum between merging tendons and vessels. A common mnemonic is T om, D ick, AN d H arry, which correlates with the anterior to posterior progression of T ibialis posterior tendon, flexor D igitorum tendon, posterior tibial A rtery, posterior tibial N erve, and flexor H allucis longus tendon.

Indications

  • Wound repair or exploration of the calcaneal or plantar regions of the foot
  • As part of an ankle block required to manipulate a fractured or dislocated ankle (A combination of posterior tibial, saphenous, superficial peroneal, deep peroneal, and sural nerve blocks results in complete block of sensory perception beneath the ankle, as pictured below.)

Areas of anesthetization to complete an ankle block. This block requires anesthetization of 5 nerves for complete sensory block below the ankle.

The areas to anesthetize include a line along the anterior ankle for the superficial peroneal nerve (blue line), the deep peroneal nerve (red star), the saphenous nerve (pink star), the sural nerve (green arrow), and the posterior tibial nerve (orange arrow).

  • Relief of tarsal tunnel syndrome
  • Incision and drainage of an abscess in the calcaneal or plantar regions of the foot
  • Foreign body removal in the calcaneal or plantar regions of the foot

Contraindications

  • Allergy to anesthetic solution or additives (eg, ester, amide)
  • Injection through infected tissue
  • Severe bleeding disorder or coagulopathy
  • Preexisting neurological damage
  • Patient uncooperativeness (Pediatric or elderly patients may need sedation.)

Anesthesia

  • The 2 main classes of local anesthetics currently in use are amino esters and amino amides. Both inhibit ionic fluxes required for the initiation and conduction of nerve impulses. Lidocaine, the most commonly used anesthetic, has a fast onset of action and a duration of action of 30-120 minutes, which is increased to 60-400 minutes with the addition of epinephrine. 
  •  The total cumulative dose of lidocaine to be infiltrated is 5 mg/kg (not to exceed 300 mg) if lidocaine without epinephrine is used, and 7 mg/kg (not to exceed 500 mg) if lidocaine with epinephrine is used.
  • Anesthetic preparations that contain epinephrine are commonly used in the emergency department. Epinephrine induces vasoconstriction, decreasing the amount of local bleeding at the site of injection. In addition, it increases the duration of action of the anesthetic with which it is combined. Despite these advantages, the vasoconstrictive properties of epinephrine may contribute to tissue hypoxia, and its use should be avoided in areas of poor perfusion (ie, fingers, toes, penis, ears, nose).
  • Topical anesthetics may be needed in children or uncooperative adults.

Equipment

  • Needle, 4 cm, 25 gauge (ga)  
  • Needle, 18 ga
  • Syringe, 10 mL
  • Marking pen
  • Sterile gloves
  • Antiseptic solution (eg, povidone iodine [Betadine], chlorhexidine gluconate [Hibiclens]) with skin swabs
  • Alcohol swabs
  • Sterile drape
  • Lidocaine 1%, 10 mL
  • Facial mask with eye shield
  • Sterile gauze

Equipment needed for the regional block.

Positioning

  • Position the patient supine and as comfortably as possible.
  • Alternatively, the patient may sit and face the physician.

Next >> Technique

Source Emedicine.medscape.com
Thứ bảy, 18 Tháng 9 2010 08:06

Radial Nerve Block

Written by

Introduction

Radial nerve block is a simple procedure that can be performed at various levels along the course of the radial nerve. Surgical anesthesia, postoperative analgesia, and palliative measures for acute painful conditions are all indications for radial nerve block.

Radial nerve anatomy

The radial nerve is 1 of the 4 important branches of the posterior cord of the brachial plexus and has the root values of C5, C6, C7, C8, and T1. The mnemonic STAR (Subscapular, Thoracodorsal, Axillary, Radial) is an easy way to remember the 4 branches.

A brachial plexus schematic, radial nerve sensory distribution, and radial nerve course are shown in the images below.

Brachial plexus schematic.

Brachial plexus schematic.

Sensory distribution of the radial nerve.

Sensory distribution of the radial nerve.

Course of the radial nerve.

Course of the radial nerve.

In the axilla, the radial nerve descends behind the axillary and brachial arteries, passes between the long and medial heads of the triceps muscle, and enters the posterior compartment of the arm. It then winds in the spiral groove of the humerus with the profunda brachii vessels. Just above the elbow, it pierces the lateral intermuscular septum and continues downward into the cubital fossa between the brachialis and brachioradialis muscles. At the level of the elbow (lateral epicondyle), it divides into superficial and deep branches.

  • Branches of the radial nerve in the axilla
    • Cutaneous branch - Posterior brachial cutaneous nerve
    • Muscular branches - Long and medial heads of triceps
  • Branches of the radial nerve in the spiral groove
    • Cutaneous branches - Lower lateral brachial cutaneous nerve, posterior antebrachial cutaneous nerve
    • Muscular branches - Lateral and medial heads of the triceps, anconeus
  • Branches of the radial nerve in the arm
    • Articular branch - Elbow joint
    • Muscular branches - Brachialis, brachioradialis, extensor carpi radialis longus

The superficial branch of the radial nerve descends lateral to the radial artery and passes backward under the tendon of the brachioradialis muscle. It then continues distally between the brachioradialis and supinator muscles before descending onto the dorsum of the hand. It provides cutaneous innervation to the lateral two thirds of the dorsum of the hand and the lateral two and one half proximal phalanxes.

The deep branch of the radial nerve winds around the lateral part of the neck of the radius and enters the posterior compartment of the forearm. It descends between the superficial and deep layers of the supinator muscle and reaches the dorsal aspect of the interosseous membrane. It innervates the extensor carpi radialis brevis, supinator, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and extensor indicis. It also provides articular branches to the wrist and carpal joints.

Indications

  • Surgical anesthesia along the course of the radial nerve
  • Supplement to brachial plexus block
  • Postoperative analgesia
  • Acute pain emergencies in the course of the radial nerve
  • Radial tunnel syndrome: This is a painful condition of the radial nerve. To distinguish radial tunnel syndrome from tennis elbow, palpate the lateral epicondyle. In tennis elbow, this palpation reveals tenderness over the lateral epicondyle that is absent in radial tunnel syndrome.
  • Cheiralgia paresthetica or Wartenberg syndrome: This syndrome is secondary to compression of the radial nerve distal to the musculospiral grove. Compression occurs because of the brachioradialis muscle during forearm pronation. The syndrome is manifested by painful paresthesias and decreased sensation over the dorsum of the hand.

Contraindications

  • Patient refusal
  • Infection at the site
  • Coagulopathy
  • Allergy to available local anesthetic

Anesthesia

  • In adults, the radial nerve block is well tolerated with reassurance from the practitioner. Skin infiltration with lidocaine 1% 0.5-1 mL suffices to facilitate needle entry. For more information, see Local Anesthetic Agents, Infiltrative Administration.
  • Extremely anxious patients may benefit from oral diazepam 10 mg the night before or intravenous midazolam (1-2 mg, titrated to sedation) prior to the block.
  • General anesthesia may be needed for pediatric patients.
Choice of local anesthetic for the block

The choice of the type and concentration of local anesthetic for radial nerve blockade is based on the desired duration. Alkalinization of mepivacaine and lidocaine with sodium bicarbonate results in faster time to onset of anesthesia. Table 1 provides onset times and duration for some commonly used local anesthetics mixtures.

Table 1. Local Anesthetic for Radial Nerve Block

Local Anesthetic Onset, min Anesthesia Duration, h Analgesia Duration, h
Mepivacaine 1.5% 15-20 2-3 3-5
Lidocaine 2% 10-20 2-5 3-8
Ropivacaine 0.5% 15-30 4-8 5-8
Ropivacaine 0.75% 10-15 5-10 6-24
Bupivacaine 0.5% (or levobupivacaine) 15-30 5-15 6-30

 

Equipment

  • Alcohol, povidone-iodine solution (Betadine), or chlorhexidine (Hibiclens) preparatory solution
  • Syringe, 1 mL, for local anesthetic
  • Syringe, 5 mL, for the block
  • Needle, 1 in, 25-27 gauge (ga), for the block
  • Lidocaine 1%, bupivacaine 0.5%, or ropivacaine 0.5%; 5 mL
  • Depot corticosteroid (eg, methylprednisolone acetate [DepoMedrol] 40 mg, triamcinolone acetonide [Kenalog] 40 mg)
  • Gauze, 2 X 2
  • Adhesive bandage
  • Sterile gloves
  • All resuscitative equipment
  • Standard monitoring equipment

Positioning

  • Position the patient comfortably with the affected arm well supported.
  • Usually, the supine position is preferred, with the arm supported on the side.

Technique

Block at the humerus level

  • Position the patient supine with the arm abducted 45º and the hand resting comfortably on the abdomen. Radial nerve block land marks are shown in the image below.

Radial nerve block at the humerus level.

Radial nerve block at the humerus level.
  • Palpate deeply between the heads of the triceps muscle and the brachialis muscle to identify the musculospiral groove.
  • Prepare the skin with an antiseptic solution.
  • To facilitate needle entry, infiltrate the injection site with lidocaine 1% 0.5-1 mL.
  • Insert the 25-ga 1-in needle perpendicularly toward the musculospiral groove.
  • Identify the nerve by paresthesia or nerve stimulator technique. If no response is elicited, redirect the needle slightly more anteriorly or posteriorly until the response is elicited.
  • Aspirate gently to identify intravascular location of the needle.
  • If the aspiration is negative, slowly inject 7-10 mL of the local anesthetic in slow increments, with intermittent aspiration. The image below shows landmarks for a radial nerve block at the humerus level.

Radial nerve block at the humerus level.

Radial nerve block at the humerus level.

Block at the elbow level

  • Position the patient as described above.
  • Identify the lateral margin of the biceps tendon at the elbow crease by flexing the elbow.
  • Prepare the skin with an antiseptic solution.
  • Insert the needle just lateral to the tendon and advance it in a slightly medial and cephalad direction toward the humerus. Landmarks for a radial nerve block at the elbow are shown in the image below.

Radial nerve block at the elbow. The bicipital ap...

Radial nerve block at the elbow. The bicipital aponeurosis is visible. Needle entry is just lateral to the bicipital aponeurosis.
  • Identify the nerve with paresthesia, nerve stimulation, ultrasonographic guidance, or a combination thereof.
  • After negative aspiration, slowly inject 7-10 mL of the local anesthetic. Landmarks for a radial nerve block at the elbow are shown below.

Radial nerve block at the elbow.

Radial nerve block at the elbow.

Block at the wrist level

  • The radial nerve block at the wrist level (landmarks shown below) is essentially a field block and requires a more extensive infiltration because of its less predictable anatomic location and division into multiple, smaller, cutaneous branches.

Radial nerve block at the wrist level.

Radial nerve block at the wrist level.
  • Inject 5 mL of local anesthetic subcutaneously, just above the radial styloid, aiming medially. Additional landmarks for a radial nerve block at the wrist are shown below.

Radial nerve block at the wrist.

Radial nerve block at the wrist.
  • Extend the infiltration laterally, using an additional 5 mL of local anesthetic.

Pearls

  • The radial nerve block may be performed solely or in combination with ulnar and median nerve blocks.
  • The radial nerve block may supplement the brachial plexus block. If performing a brachial plexus block at the humeral canal, block the radial nerve before blocking the ulnar nerve.
  • This block can be performed at the humerus, elbow, and wrist levels.
  • Lidocaine, bupivacaine, ropivacaine are the local anesthetics typically used for this procedure.
  • Surface landmarks, paresthesia, nerve stimulation, and ultrasonographic guidance are all helpful in performing the radial nerve block.
  • Take care to avoid intraneural or intravascular injection of the local anesthetic.

Complications

  • Complications after wrist block are typically limited to residual paresthesia due to an inadvertent intraneuronal injection. Systemic toxicity is rare because of the distal location of the blockade.
  • Complications may be avoided by taking preventive measures (see Table 2).
Table 2. Prevention of Complications in Radial Nerve Block*  
Complication Prevention
Infection Use aseptic technique
Hematoma Limit number of insertions (1-2 for superficial block)

Use 25-ga needle to avoid puncturing superficial veins

Vascular puncture Do not use epinephrine with wrist and finger blocks
Nerve injury Do not inject when patient reports pain on injection

Do not inject when high pressure is detected on injection

Other injury Instruct the patient on care of the insensate extremity

*Table adapted from Wrist Block, New York School of Regional Anesthesia 

Source Emedicine.medscape.com

Thứ sáu, 17 Tháng 9 2010 16:20

Median Nerve Block

Written by

Introduction

  • Median nerve blocks at the wrist, either alone or in combination with blockade of the ulnar and radial nerves, are useful emergency department (ED) procedures. Compared to local anesthesia, nerve blocks provide greater efficacy and coverage of anesthesia useful for more complicated wounds or procedures involving the hand. In general, adequate anesthesia is a prerequisite to proper irrigation, examination, and repair of all wounds.
  • The median nerve can be blocked at multiple sites along its passage through the upper extremity. However, only the wrist block is commonly used in the ED setting.

Anatomy

  • Safe and effective application of the median nerve block requires a thorough understanding of the regional anatomy (see images below).

Wrist anatomy cross-section.

Wrist anatomy cross-section.

  Wrist anatomy.

Wrist anatomy.
  • A median nerve block at the wrist provides anesthesia and analgesia to the palmar surfaces of the lateral two-thirds of the palm, the thumb, the index and middle fingers, and one half of the ring finger (see image below).

Sensory innervation of the median nerve on the pa...

Sensory innervation of the median nerve on the palmar hand.
  • The median nerve passes through the carpal tunnel and gives rise to the palmar digital nerves supplying sensation to the lateral digits and motor innervation of the lateral two lumbricals. Sensation in the palm is supplied by superficial branches of the median nerve arising in the distal forearm. A recurrent branch of the median nerve also provides motor function to the thenar muscles.

Indications

  • For simple lacerations, nerve blocks at the wrist may be slower and less reliable than local infiltration or digital block. However, they can be particularly useful in the following ED applications:
    • Simultaneous injury to multiple digits
    • Large abrasions or avulsions of the hand that require thorough irrigation, debridement, or both
    • Avoiding distortion of anatomy in areas with limited subcutaneous tissue or tissue that is already excessively swollen
    • Simultaneously anesthetizing several lacerations in close proximity
  • In many of these situations, the median nerve block can be combined with ulnar or radial blocks at the wrist to achieve the desired coverage.

Contraindications

  • Allergy to anesthesia: Consider using procaine (an ester anesthetic) in patients with true allergy to lidocaine or bupivacaine (amide anesthetics).
  • Anatomic variation: Median nerve block may be contraindicated in the presence of prior surgery or injury at the wrist, proximal vascular grafts, or arteriovenous (AV) fistula.
  • Additional injuries: The presence of additional injuries proximal to the wrist may necessitate a more proximal nerve block. Bier blocks or nerve blocks at the brachial plexus are more effective but require additional expertise to employ.
  • Hepatic failure: Amide anesthetics, including lidocaine and bupivacaine, are metabolized by the liver. Take extra care to minimize systemic toxicity in patients with hepatic failure.

Anesthesia

  • The choice of anesthetic depends upon the specific procedure to be performed and the desired duration of effect.
  • The most commonly used agent is 2% lidocaine. The higher concentration increases the concentration gradient in the tissue, allowing for faster spread of the agent from a smaller volume.
  • Bupivacaine (0.25%-0.5%) can also be used for longer duration of anesthesia. Bupivacaine is not advised by the manufacturer for children younger than 12 years because of a lack of safety data.
  • Hypersensitivity reactions are rare and may be due to preservatives rather than the anesthetic itself. Lidocaine and bupivacaine are both amide anesthetics and may have allergic cross-sensitivity. Procaine, an ester anesthetic, may be tolerated in patients with true allergic reactions to lidocaine.
  • The maximum dose should be considered but is not frequently an issue for minor injuries in adults. Nerve blocks may also require less total dose than local injection.
  • As with digital nerve blocks, epinephrine-containing solutions have been traditionally avoided because of the theoretical risk of extremity ischemia from arterial constriction. However, reliable reports of this complication, even in digital nerve blocks, are lacking, and recent studies of epinephrine-containing solutions have shown more benefit than harm for that application. In the case of median nerve blocks, epinephrine is unlikely to decrease bleeding at the site of injury and cannot be advised for this purpose.
  • As lidocaine solutions are preserved at a low pH level, they may also be buffered with sodium bicarbonate (NaHCO 3 ) to decrease the pain of administration.
  • The details of 2% lidocaine (plus NaHCO 3 ) are as follows:
    • 2% lidocaine contains 20 mg/mL
    • Onset: 10-20 min
    • Duration: 2-5 hours
    • Maximum dose: 4 mg/kg; not to exceed 300 mg
  • The details of 0.5% bupivacaine are as follows:
    • 0.5% bupivacaine contains 5 mg/mL
    • Onset: 10-30 min
    • Duration: 5-15 hours
    • Maximum dose: 2.5 mg/kg; not to exceed 175 mg

For information comparing local anesthetics and a thorough discussion regarding allergic reactions to local anesthetics, see Local Anesthetic Agents, Infiltrative Administration.

Equipment

  • The field should be sterilely prepared. Chlorhexidine solution is the preferred agent for many practitioners and is recommended by the CDC for optimal sterility in other applications.
  • A 25- to 27-gauge needle is appropriate.
    • A smaller needle is less likely to cause direct nerve damage and causes less pain with injection.
    • However, smaller needles do have disadvantages. With a smaller needle, confirmation of intravascular location by pulling back the plunger is more difficult. Also, a smaller needle may also elicit less paresthesia prior to injection, if placed intraneuronally.

Positioning

  • Positioning is critical to all procedures in the ED. Attention to practitioner and patient comfort maximizes success.
  • Elevate the bed and place the patient’s arm on a Mayo stand or other support.
  • Place a small roll under the wrist to extend the wrist slightly.

Technique

  • Prior to any nerve block, perform and document a thorough neurovascular examination. Two-point discrimination is performed in the region to be blocked, with comparison to the contralateral limb.
  • At the wrist, the median nerve lies within the carpal tunnel, deep and radial to the palmaris longus (PL) tendon and medial to the flexor carpi radialis (FCR) tendon.
  • Injection is performed by insertion of the needle perpendicular to the skin between the PL and FCR tendons, angled slightly to place the needle tip directly beneath the PL (see image below). The injection is made 2-3 cm proximal to the distal crease of the wrist to avoid injecting within the carpal tunnel.

Median nerve block: Injection is performed betwee...

Median nerve block: Injection is performed between the tendons of the flexor carpi radialis (FCR) and the palmaris longus (PL), proximal to the crease of the wrist.
  • The location of the PL and FCR tendons can be highlighted by having the patient flex the middle finger against resistance or pinch the thumb and little finger together.
  • Some individuals lack the PL tendon, in which case the injection is made 5 mm ulnar (medial) to the FCR tendon, or approximately at the midpoint of the wrist.
  • The needle is inserted to a depth of 1-2 cm. Passage through the fibrous flexor retinaculum may be felt. The nerve lies more superficial than one may expect. However, injecting in a space too deep is better than in a space too shallow, as the retinaculum prevents anesthetic from reaching the nerve if injected too superficially.
  • An anesthetic volume of 3-5 mL is appropriate. Aspiration to prevent intravascular injection is generally advised to prevent systemic toxicity. If resistance to injection is met or paresthesia is elicited on needle insertion, the needle should be repositioned slightly more medial to avoid intraneuronal injection.
  • To include the peripheral (palmar) branches, a small wheal of anesthetic is placed subcutaneously as the needle is withdrawn and massaged gently over the volar wrist.
  • After injection, adequate time must be allowed for full effect (at least 10 minutes) before the desired procedure is performed on the hand.
  • An alternative method for performing these blocks under dynamic ultrasonographic guidance has recently been evaluated for use in the ED.

Pearls

  • As with most procedures, proper positioning of the patient and practitioner is critical to success and safety.
  • Give the patient instructions on care for the anesthetized hand and fingers, especially when using long-acting anesthetics. Anesthetized extremities are at greater risk of injury.

Complications

  • Infection: This complication should be extremely rare when proper technique is used.
  • Hematoma: This complication is more likely to occur if multiple punctures are made. Proper technique should keep the needle far from the radial or ulnar arteries.
  • Nerve injury: Reposition the needle if increased pain or paresthesia is noted, and avoid injection against resistance.
  • Vascular compromise: Avoidance of epinephrine-containing solutions is generally recommended, although this risk may be exaggerated.
  • Source Emedicine.medscape.com

      

Thứ năm, 16 Tháng 9 2010 17:05

Deep Peroneal Nerve Block

Written by

Introduction

Deep peroneal nerve block is one of the 2 deep nerve blocks at the level of the ankle. The deep peroneal nerve block is easy to perform and may constitute part of an ankle block.

The deep peroneal nerve block is useful for anesthesia and postoperative analgesia to surgeries of the first web space (eg, Morton neuroma). It can also be used to treat chronic pain conditions like anterior tarsal tunnel syndrome.

Anatomy

The common peroneal nerve (root values: L4, L5, S1, and S2) winds around the fibula through the fibular tunnel. The tunnel is bordered by the peroneus longus tendon and the fibula. Just distal to the fibular tunnel, the nerve divides into the superficial and deep peroneal nerves. The deep peroneal nerve (or the anterior tibial nerve) begins at the bifurcation of the common peroneal nerve, between the fibula and upper part of peroneus longus. In the distal one third of the ankle, the nerve is located between the tibialis anterior and extensor hallucis longus muscles and is superficial to the anterior tibial artery. At an average distance of 12.5 mm proximal to the ankle, the nerve crosses deep to the extensor hallucis longus tendon and courses between the extensor hallucis longus and extensor digitorum longus tendons. The image below shows the nerve and adjacent structures.

Deep peroneal nerve and adjacent structures.
Deep peroneal nerve and adjacent structures.

In the leg, the deep peroneal nerve supplies muscular branches to the tibialis anterior, extensor digitorum longus, peroneus tertius, and extensor hallucis longus. It also provides an articular branch to the ankle joint.

The deep peroneal branch continues into the foot along with the tibial artery and the vein. It passes beneath the dense superficial fascia of the ankle. Then it divides into lateral terminal and medial terminal branches.

The lateral terminal branch (external branch) passes across the tarsus anterolaterally, enlarges and supplies the extensor digitorum brevis. From the enlargement, 3 minute interosseous branches (dorsal interosseous nerves) are given off, which supply the tarsal joints and the metatarsophalangeal joints of the 2nd, 3rd, and 4th toes. The medial terminal branch (internal branch) accompanies and runs medial to the dorsalis pedis artery along the dorsum of the foot. At the first interosseous space, it divides into dorsal digital nerves, which provide sensory innervation to the first webspace and the adjacent dorsum of the foot.

Two cm distal to the intermalleolar line, the following structures (from medial to lateral) are related to the deep peroneal nerve:

  1. Tendon of tibialis anterior
  2. Tendon of extensor hallucis longus
  3. Dorsal pedis artery
  4. Deep peroneal nerve
  5. Tendon of extensor digitorum longus

Blocking the following five nerves (3 superficial and 2 deep) results in complete block of sensory perception beneath the ankle:

  1. Superficial peroneal nerve
  2. Saphenous nerve
  3. Sural nerve
  4. Deep peroneal nerve
  5. Posterior tibial nerve

All 5 nerves should be blocked if a tourniquet is used for foot surgery.

Indications

  • Surgeries involving the first web space of the foot (eg, Morton neuroma)
  • Component of ankle block (Ankle block is preferred for foot surgeries in patients who may not tolerate epidural or spinal anesthetic.)
  • Treatment of acute or chronic pain conditions involving the foot with entrapment of the deep peroneal nerve at the anterior tarsal tunnel (Anterior tarsal tunnel syndrome is characterized by persistent aching of the dorsum of the foot that is worse at night and is made better by moving the affected toes and ankle. Sometimes, patients experience weakness of toe extensors. Patients with diabetes may be more prone to this condition. It can occur after prolonged squatting or leaning forward.)
  • As a palliative measure and a part of multimodal approach to pain management of acute pain from foot fracture or gouty arthritis
  • As a prelude to neurolysis or radiofrequency ablation of the deep peroneal nerve.

Contraindications

  • Patient refusal
  • Infection at the injection site
  • Coagulopathy

Anesthesia

  • Infiltrate area of skin for nerve block with 0.5-1 mL of lidocaine 1%.
  • For more information, see Local Anesthetic Agents,

Equipment

  • Alcohol, povidone-iodine (eg, Betadine), or chlorhexidine (Hibiclens) preparatory solution.
  • Syringe, 5 mL, 25-27 gauge 1-inch needle
  • Anesthetic, 5 mL (lidocaine 1%, bupivacaine 0.5%, or ropivacaine 0.5%)
  • Depot corticosteroid (eg, methylprednisolone acetate [Depo-Medrol] 40 mg, triamcinolone acetonide [Kenalog] 40 mg)
  • Gauze, 2 X 2
  • Sterile gloves
  • All resuscitative equipment
  • Standard monitors
  • Adhesive bandage

Positioning

  • Position the patient supine with the toes dorsiflexed to identify the tibialis anterior, extensor hallucis longus, and extensor digitorum longus tendons.

Technique

The deep peroneal nerve is traditionally located by identifying the surface landmarks, shown below. Other methods of identifying the injection site include invoking paresthesia, using a nerve stimulator, and ultrasonographic guidance.

Foot with surface landmarks
Foot with surface landmarks. Note the course of the deep peroneal nerve and its relation to the dorsalis pedis artery.

Perimalleolar approach

  • Perform a careful neurological assessment prior to the procedure.
  • Identify the tendon of extensor hallucis longus by big toe dorsiflexion against resistance. A groove is felt just lateral to the tendon.
  • The deep peroneal nerve lies lateral to the tendon and the dorsalis pedis artery. Lateral to the nerve is the tendon of the extensor digitorum longus. The needle entry site is about 2 cm distal to the intermalleolar line, just lateral to the dorsalis pedis artery pulse.
  • After the skin is prepared, raise a skin wheal with the 0.5-1 mL of the local anesthetic.
  • Next, advance the same needle and syringe that contains the local anesthetic through the skin in a perpendicular manner until bone is encountered, usually within 2-3 cm.
  • Withdraw the needle slightly to prevent periosteal injection.
  • Patients may experience paresthesia in the first web space. If paresthesia occurs, withdraw the needle slightly until the paresthesia disappears.
  • After careful negative aspiration for heme, inject 2 mL of the local anesthetic.
  • To increase the block success, the needle may be redirected 30º medially and laterally and an additional 2 mL of the anesthetic injected.
  • Remove the needle and apply firm pressure to prevent bleeding.
  • If the condition has an inflammatory component, methylprednisolone 40 mg or triamcinolone 40 mg may be added to the injectate.
  • If a nerve stimulator is used (2-3 mA at 0.1 ms), extension of the lateral 4 toes due to muscle twitch of the extensor digitorum brevis may be used to locate the nerve.

Inframalleolar or midtarsal approach

  • Insert the needle immediately lateral to the extensor hallucis longus tendon but medial to the dorsalis pedis artery.
  • After negative aspiration, inject 5 mL of local anesthetic as described above.

Pearls

  • The deep peroneal nerve is one of the 2 deep nerves at the ankle. The deep peroneal nerve may be blocked as a part of a total ankle block.
  • The deep peroneal nerve innervates the first web space.
  • At the malleolar level, the deep peroneal nerve is located between the tendons of extensor hallucis longus and extensor digitorum longus, in close proximity to the dorsalis pedis artery.
  • To increase the block success, redirect the needle 30º and inject additional local anesthetic after the initial injection.
  • Careful neurological assessment is important prior to the procedure; it helps avoid later attribution of preexisting neurological deficits to the nerve block.

Complications

The block is essentially safe block to perform, but some complications can occur.

  • Intravascular injection: The dorsalis pedis artery should be carefully palpated to minimize the chance of intravascular injection of local anesthetic.
  • Ecchymosis and hematoma: These complications can be avoided by applying firm pressure to the injection site after the injection.
  • Paresthesia: To avoid needle-induced trauma to the nerve, withdraw the needle slightly before the injection.
Source Emedicine.medscape.com 
Thứ ba, 14 Tháng 9 2010 20:04

Digital nerve blocks

Written by

Introduction

Digital nerve blocks are important tools for the emergency medicine clinician. Injuries or infections of the digits are extremely common. Adequate analgesia is essential to properly address the presenting condition and to minimize the patient's discomfort. Digital blocks are useful in many scenarios in which local infiltration of an anesthetic would require several injections into the already painful site of injury. Furthermore, local infiltration around the wound may create increased swelling, making the repair more difficult. Several techniques are available for performing digital blocks.

Relevant anatomy

Each digit is innervated by 4 digital nerves. In the upper extremity, the digital nerves arise from the median, ulnar, and radial nerves. The 2 palmar digital nerves innervate the palmar aspect of the digit and the nail bed, whereas the dorsal nerves innervate the dorsum of the digit (see images below). The tibial and peroneal nerves branch off into the digital nerves of the lower extremities, which follow a pattern of distribution analogous to those of the upper extremity.

Palmar digital nerves.

Dorsal digital nerves.

Indications

Digital blocks are indicated for any minor surgery or procedure of the digits. These include, but are not limited to, the following:

  • Large irregular lacerations
  • Lacerations involving the nail or the nail bed
  • Ingrown nails
  • Felon or paronychia
  • Trephination of subungual hematoma
  • Digit dislocations or fractures

Contraindications

  • Compromised digit circulation
  • Infected injection site
  • Known allergy to anesthetic

Anesthesia

Local anesthetic agents have the basic structure of an aromatic and a hydrophilic, separated in the middle by an amino-ester or an amino-amide. This forms the basis of classification of local anesthetics into 2 groups: the ester-type agents (eg, procaine) and the amide-type agents (eg, lidocaine).

The choice of agent is based on the desired duration of analgesia and the patient’s allergy profile. Lidocaine is the most commonly used anesthetic. If longer anesthesia is required, another amide anesthetic, such as bupivacaine, can be used. If the patient is known to be allergic to lidocaine, an ester-type anesthetic, such as procaine, can be substituted. Table 1 summarizes the properties of commonly used agents.

Table 1. Commonly Used Local Anesthetics and Their Properties

Agent

 

Maximum Adult Dose (mg)/Procedure*

 

Onset (min)

 

Duration

 

Lidocaine

 

300

 

2-5

 

1-2 h

 

Procaine

 

500

 

2-5

 

15-45 min

 

Bupivacaine

 

175

 

2-5

 

4-8 h

 

Agent

 

Maximum Adult Dose (mg)/Procedure*

 

Onset (min)

 

Duration

 

Lidocaine

 

300

 

2-5

 

1-2 h

 

Procaine

 

500

 

2-5

 

15-45 min

 

Bupivacaine

 

175

 

2-5

 

4-8 h

 

*Administer by small incremental doses.

Local anesthetics are to be used without epinephrine in the digits to avoid vasoconstriction of adjacent arteries, which may lead to ischemia or infarction of local tissues. Despite studies that have shown epinephrine to be safe in these circumstances, epinephrine is traditionally avoided in the digits. The block should be performed cautiously in areas where nerve function is compromised. Small volumes of anesthetic should be used to minimize local swelling, especially in cases in which compartment syndrome is being considered.

Equipment

  • Sterile gloves, drapes, and gauze pads
  • Povidone-iodine (Betadine) solution
  • Syringe, 5-10 mL, with an 18-gauge needle for drawing up the anesthetic and a 25- to 30-gauge needle for injection
  • Local anesthetic of choice

Positioning

Depending on the technique used, the extremity position varies. See the Technique section below for detailed explanations.

Technique

Several different techniques can be used to anesthetize the digits: the web-space block, the transthecal block, the 3-sided digital block, and the 4-sided ring block. Standard sterile precautions should be followed for all of the described procedures.

Web-space block

This method is very effective in achieving adequate anesthesia and is probably the least painful.

 

Needle position for web-space block.

 

  • Place the patient’s hand on a sterile field with the palm down.
  • Hold the syringe perpendicular to the digit and insert the needle into the web space, just distal to the metacarpal-phalangeal (MP) joint (see image below).
  • Slowly inject the anesthetic in the dorsal aspect of the web space.
  • Slowly advance the needle straight down toward the volar aspect of the web space, slowly infiltrating the surrounding tissues of the web space (see video below). The needle should not pierce the volar aspect of the web space.
  • Withdraw the needle and repeat the procedure on the other web space of the involved digit.
  • The toes (except the great toe) can be effectively anesthetized in the same manner.

Transthecal block

Originally described by Chiu in 1990, this technique is also known as the flexor tendon sheath digital block. While treating trigger finger by injecting steroids and lidocaine into the tendon sheath, Chiu noted that anesthesia of the entire digit was achieved. Although adequate anesthesia is achieved with a single injection, this injection is painful because the needle pierces the very sensitive skin of the palm. Studies have shown that this type of block is as effective as traditional ring blocks in achieving adequate anesthesia.

  • Place the patient’s hand on the sterile field with the palm up.
  • Locate the flexor tendon sheath by palpating it at the distal palmar crease.
  • Insert the needle at a 45-degree angle just distal to the distal palmar crease (see image below)

Needle position for transthecal block.
  • Inject the anesthetic, it should flow freely. If resistance is met, reposition the needle by slowly withdrawing it.
  • A modified version of this technique can also be used effectively.
  • Position the patient’s hand with the palm facing up.
  • Insert the needle at a 90-degree angle at the metacarpal crease until bone is hit.
  • Withdraw the needle slightly and inject the anesthetic.
  • During the injection, use the nondominant hand to apply pressure just proximal to the injection site, to direct the flow distally (see image below).

Modified transthecal block.

Three-sided digital block

This type of digital block is effective in anesthetizing the great toe, but it can be used for any digit.

  • Place the patient’s extremity volar/plantar side down.
  • Insert the needle at a 90-degree angle at the lateral aspect of the digit, just distal to the metatarsal-phalangeal joint (see image below).

Lateral injection for 3-sided digital block.
  • Slowly inject the anesthetic as the needle is advanced toward the volar/plantar side, without piercing the volar skin.
  • Slowly withdraw the needle and redirect it medially.
  • Advance the needle slowly from lateral to medial side while the anesthetic is injected (see image below).

 
Lateral to medial injection for 3-sided digital block.
  • Withdraw the needle.
  • Make another injection over the already anesthetized skin at the medial aspect of the digit, with the needle at 90 degrees, advancing it from the dorsal to ventral aspect, as was done on the lateral side (see image below).

 
Medial injection for 3-sided digital block.

Four-sided ring block

This method is an extension of the 3-sided block. After the 3-sided block is performed, a third injection is performed. Insert the needle at the lateral aspect of the digit on the volar/plantar side and advance it medially as the anesthetic is slowly injected. This technique is less favored because of the potential for ischemic complications.

Wing block procedure

When only the distal part of the digit is involved (eg, nail injury), a wing block procedure can be used instead of a digital block.

  • Position the extremity with the volar/plantar side down.
  • Hold the needle perpendicular to the long axis of the digit and at 45 degrees to the plane of the sterile field.
  • Insert the needle 3 mm proximal to an imaginary point where a linear extension of the lateral and proximal nail folds would intersect (see image below).

 
Wing block technique.
  • Inject the anesthetic along the proximal nail fold.
  • Slowly withdraw the needle and redirect it toward the lateral nail fold.
  • This may be performed on the opposite side of the nail as necessary.

Pearls

  • Avoid epinephrine use in the digits; a clamped Penrose drain can be used to limit bleeding.
  • Limit the patient’s discomfort by using a smaller needle, injecting slowly, and using small amounts of anesthetics.
  • Anesthesia of the great toe is more difficult to achieve and requires 3-sided/4-sided ring blocks.
  • Use of sterile technique is essential to limit the risk of introducing infections (especially with the transthecal block).

Complications

Numerous potential complications and local anesthetic toxicities have been described in the literature.

Source Emedicine.medscape.com

 

  • Pain at injection site
  • Infection at injection site, especially with transthecal block
  • Wound infection: Local anesthetics have been shown to possess antimicrobial properties. Although studies have shown that use of local anesthetics does not alter incidence of wound infection, their use may produce false-negative wound cultures.
  • Local injuries: Injuries to nerves and tendons can result in long-term complications such as neuropathies and tendonitis.
  • Wound healing: Several studies have shown that local anesthetics inhibit wound healing by decreasing the tensile strength of wounds; another study showed that local anesthetics decrease local inflammatory response.
  • Inadvertent intravascular injection: This increases the risk of cardiotoxicity and neurotoxicity.
  • Allergic reactions
  • Vasovagal syncope
Thứ ba, 14 Tháng 9 2010 15:11

Local and Regional Anesthesia

Written by

Introduction

Local anesthetics provide a reversible regional loss of sensation. Local anesthetics reduce pain, thereby facilitating surgical procedures. Delivery techniques broaden the clinical applicability of local anesthetics. These techniques include topical anesthesia, infiltrative anesthesia, ring blocks, and peripheral nerve blocks.

Local anesthetics are safer than general or systemic anesthetics; therefore, they are used whenever possible. In addition, they are relatively easy to administer and readily available. Local anesthetics have been undergoing development for centuries, and, as this article illustrates, research continues to provide surgeons with pharmacologic variety and to provide patients with anesthetic agents that have superior safety and efficacy profiles.

Background

  • Although the medical world cannot cure every disease, the control of pain to ensure patient comfort should be a goal. In 1860, cocaine, the oldest anesthetic, was extracted from the leaves of the Erythroxylon coca bush. In 1884, Sigmund Freud and Karl Koller were the first to use it as an anesthetic agent during ophthalmologic procedures.
  • Procaine, a synthetic alternative to cocaine, was not developed until 1904. Procaine is an ester of para-aminobenzoic acid (PABA). As procaine is metabolized, PABA, a known allergen, is released as a metabolic product. The potential for severe allergic reactions limits the use of procaine and other ester-type anesthetic agents. Tetracaine, another ester-type anesthetic, was introduced in 1930. Tetracaine is more potent than procaine, and it causes similar allergic reactions.
  • In 1943, an alternative class of anesthetics was discovered when Lofgren developed lidocaine. This agent is an amide derivative of diethylaminoacetic acid, not PABA; therefore, it has the benefit of a low allergic potential. Since then, multiple amide-type anesthetics have been introduced into clinical use. Slight chemical alterations to the compounds have imparted beneficial characteristics, including increased duration and potency, to each. These compounds offer the surgeon more choices, and anesthetics can be appropriately matched to different procedures.

Pathophysiology

  • Reviewing the physiology of nerve conduction is important before any discussion of local anesthetics. Nerves transmit sensation as a result of the propagation of electrical impulses; this propagation is accomplished by alternating the ion gradient across the nerve cell wall, or axolemma.
  • In the normal resting state, the nerve has a negative membrane potential of -70 mV. This resting potential is determined by the concentration gradients of 2 major ions, Na+ and K+, and the relative membrane permeability to these ions (also known as leak currents). The concentration gradients are maintained by the sodium/potassium ATP pump (in an energy-dependent process) that transports sodium ions out of the cell and potassium ions into the cell. This active transport creates a concentration gradient that favors the extracellular diffusion of potassium ions. In addition, because the nerve membrane is permeable to potassium ions and impermeable to sodium ions, 95% of the ionic leak in excitable cells is caused by K+ ions in the form of an outward flux, accounting for the negative resting potential. The recently identified 2-pore domain potassium (K2P) channels are believed to be responsible for leak K+ currents.
  • When a nerve is stimulated, depolarization of the nerve occurs, and impulse propagation progresses. Initially, sodium ions gradually enter the cell through the nerve cell membrane. The entry of sodium ions causes the transmembrane electric potential to increase from the resting potential. Once the potential reaches a threshold level of approximately -55 mV, a rapid influx of sodium ions ensues. Sodium channels in the membrane become activated, and sodium ion permeability increases; the nerve membrane is depolarized to a level of +35 mV or more.
  • Once membrane depolarization is complete, the membrane becomes impermeable to sodium ions again, and the conductance of potassium ions into the cell increases. The process restores the excess of intracellular potassium and extracellular sodium and reinstates the negative resting membrane potential. Alterations in the nerve cell membrane potential are termed the action potential. Leak currents are present through all the phases of the action potential, including setting of the resting membrane potential and repolarization.

Mechanism of action

  • Local anesthetics inhibit depolarization of the nerve membrane by interfering with both Na+ and K+ currents. The action potential is not propagated because the threshold level is never attained.
  • Although the exact mechanism by which local anesthetics retard the influx of sodium ions into the cell is unknown, 2 theories have been proposed. The membrane expansion theory postulates that the local anesthetic is absorbed into the cell membrane, expanding the membrane and leading to narrowing of the sodium channels. This hypothesis has largely given way to the specific receptor theory. This theory proposes that the local anesthetic diffuses across the cell membrane and binds to a specific receptor at the opening of the voltage-gated sodium channel. The local anesthetic affinity to the voltage-gated Na+ channel increases markedly with the excitation rate of the neuron. This binding leads to alterations in the structure or function of the channel and inhibits sodium ion movement. Blockade of leak K+ currents by local anesthetics is now also believed to contribute to conduction block by reducing the ability of the channels to set the membrane potential.
  • On the basis of their diameter, nerve fibers are categorized into 3 types. Type A fibers are the largest and are responsible for conducting pressure and motor sensations. Type B fibers are myelinated and moderate in size. Type C fibers, which transmit pain and temperature sensations, are small and unmyelinated. As a result, anesthetics block type C fibers more easily than they do type A fibers. Therefore, patients who have blocked pain sensation still feel pressure and have mobility because of the unblocked type A fibers.
  • All local anesthetics have a similar chemical structure, which consists of 3 components: an aromatic portion, an intermediate chain, and an amine group (see molecular diagram below). The aromatic portion, usually composed of a benzene ring, is lipophilic, whereas the amine portion of the anesthetic is responsible for its hydrophilic properties. The degree of lipid solubility of each anesthetic is an important property because its lipid solubility enables its diffusion through the highly lipophilic nerve membrane. The extent of an anesthetic's lipophilicity is directly related to its potency.
  • Local anesthetics are weak bases that require the addition of hydrochloride salt to be water soluble and therefore injectable. Salt equilibrates between an ionized form and a nonionized form in aqueous solution. Equilibration is crucial because, although the ionized form is injectable, the nonionized base has the lipophilic properties responsible for its diffusion into the nerve cell membrane. The duration of action of an anesthetic or the period during which it remains effective is determined by its protein-binding activity, because the anesthetic receptors along the nerve cell membrane are proteins.
  • The intermediate chain, which connects the aromatic and amine portions, is composed of either an ester or an amide linkage (see molecular diagram above). This intermediate chain can be used in classifying local anesthetics.

Indications

  • Pain reduction before surgical procedures

Contraindications

  • Patient allergies may preclude the use of a particular anesthetic agent

Technique

Specific local anesthetic techniques are described in detail in the following topics:

  • Anesthesia, Regional, Digital Block
  • Anesthesia, Topical
  • Local Anesthetic Agents, Infiltrative Administration
  • Nerve Block, Deep Peroneal
  • Nerve Block, Dorsal Penile
  • Nerve Block, Dorsal Penile, Neonatal
  • Nerve Block, Inferior Alveolar
  • Nerve Block, Infraorbital
  • Nerve Block, Oral
  • Nerve Block, Median
  • Nerve Block, Mental
  • Nerve Block, Posterior Tibial
  • Nerve Block, Radial
  • Nerve Block, Saphenous
  • Nerve Block, Superficial Peroneal
  • Nerve Block, Supraorbital
  • Nerve Block, Sural

Complications

Local effects

  • Local effects are usually a result of the injection technique. These effects include pain, ecchymosis, hematoma formation, infection, and nerve laceration. Pain is always felt when a local anesthetic is injected; however, associated discomfort can be minimized by using good technique. Several factors, including needle puncture of the skin, tissue irritation resulting from the anesthetic, and distention of tissues caused by infiltration, are responsible for the discomfort associated with the use of local anesthetics.
  • Pediatric patients and patients who are extremely anxious may benefit from pretreatment of the injection area with a topical anesthetic. Pretreatment eliminates the initial pain that occurs when the needle perforates the skin. Small-diameter needles also decrease the pain associated with injection. Fortunately, for most dermatologic procedures, a 30-gauge needle can be used to infiltrate tissue.
  • Tissue irritation caused by local anesthetics is related to the acidity of the infiltrated solution; therefore, increasing the pH of the mixture can decrease associated discomfort. The addition of epinephrine to an anesthetic solution decreases the pH of the solution, making it more acidic (pH 3.5-4.5) and leading to a more painful injection. The solution can be neutralized by the addition of sodium bicarbonate 8.4% to minimize discomfort. For example, sodium bicarbonate 8.4% can be added to lidocaine with epinephrine in a 1:10 ratio to achieve a solution pH similar to that of tissue fluid (pH 7.3-7.4).
  • Discomfort associated with distension of the tissues during the injection of local anesthetics is caused by the rate of injection and the volume of fluid injected. To limit the pain, the anesthetic should be slowly administered to allow the stretch receptors time to accommodate the new volume of fluid.In addition, the volume of solution injected should be the smallest volume needed to achieve a loss of sensation at the surgical site.
  • The formation of ecchymosis or a local hematoma is a result of the perforation of cutaneous blood vessels. These complications are encountered more commonly in areas of high vascularity, including the mucous membranes, head, and genitalia. Ecchymosis and hematoma are even more pronounced when the patient has a bleeding diathesis or when the patient has been taking aspirin or other anticoagulants. If ecchymosis occurs, the patient should simply be reassured. If hematoma formation occurs, the patient should be evaluated. The hematoma may require drainage with an 18-gauge needle, followed by the application of a pressure dressing.
  • Infection is an additional local complication of anesthetic use that usually occurs when proper sterile technique is not used. Cleansing the skin surface with alcohol is adequate in otherwise clean or noninfected areas. If signs of infection are noted, treatment includes appropriate culture studies and antimicrobial therapy. If abscess formation occurs, drainage may also be required.
  • Nerve laceration, although rare, may occur during the infiltration of a local anesthetic. This complication more commonly occurs during the placement of regional blocks than the placement of other blocks. Clinical indications of nerve laceration include paresthesias, shooting or sharp stinging sensations, and excessive pain during needle insertion. Paresthesias of the infraorbital nerve are characterized by sharp or shooting sensations involving the upper lip, nasal ala, and upper teeth.
  • If the needle is suspected to have entered or lacerated a nerve, it should be withdrawn slowly and deliberately by 1-2 mm, until the paresthesias are no longer present. The needle should never be advanced further, moved laterally, or inserted into the foramen, because these maneuvers further increase the risk of nerve laceration. Although dysesthesias may remain for an extended duration, in most patients, the nerve regenerates and sensation normalizes over time.
  • Tendon injury is an inherent aspect of transthecal digital anesthesia since the needle is pushed through the tendon. This may cause persistent discomfort lasting 1-2 days post surgery. Tendon sheath infection and late occurrence of trigger finger have also been reported.
  • Cutaneous adverse effects that have been reported with the most commonly used topical anesthetic EMLA include itching, burning, pain, pallor, erythema, edema, and purpura. Irritant dermatitis, allergic contact dermatitis, and contact urticaria have also been reported, but these are very unusual.
  • Amethocaine may induce an urticarial reaction at the site of application, and the risk of such a reaction seems to be significantly higher when amethocaine is used over the antecubital fossa and in younger children.

Systemic effects

  • Systemic effects usually occur when blood concentrations of local anesthetic increase to toxic levels. Effects are most often encountered after the unintentional intravenous injection or administration of an excessive dose of an anesthetic. Adding a vasoconstrictor (eg, epinephrine) can reduce the systemic absorption of an anesthetic. When using topical anesthetics, strict adherence to the maximal dose or area recommended is advised; additionally, great caution must be exercised when using topical anesthetics on mucosal surfaces because of the much greater absorption.
  • Importantly, remember that (1) the metabolism of ester anesthetics is decreased in patients with deficient pseudocholinesterase activity and (2) the metabolism of amide anesthetics in patients who are taking medications that inhibit the cytochrome P-450 system is decreased. In addition, the potency of an anesthetic is directly correlated with the potential for toxicity. Allergic reactions, although systemic, are not related to serum levels of the anesthetic, but rather, they are considered idiosyncratic and can occur at any dose.
  • Maximal safe doses of lidocaine for local anesthesia have been determined. For adults, a maximum of 4.5 mg of lidocaine per kilogram of body weight can be administered, whereas as much as 7 mg/kg can be used if the lidocaine solution has 1:100,000 epinephrine added as a vasoconstrictor. For children, lower maximal doses are recommended; only 1.5-2.5 mg/kg of plain lidocaine and 3-4 mg/kg of lidocaine with epinephrine should be used.
  • Systemic toxicity resulting from excessive blood levels of anesthetics is clinically manifested as adverse reactions in the CNS and cardiovascular system. The CNS is affected in a predictable and dose-dependent fashion. As serum levels of lidocaine increase, effects on the CNS become more severe.
  • Any physician who uses local anesthetics must be aware of the signs and symptoms of systemic toxicity. At serum lidocaine levels in the range of 1-5 mcg/mL, patients may complain of tinnitus, lightheadedness, circumoral numbness, diplopia, or a metallic taste in the mouth. In addition, they may complain of nausea and/or vomiting, or they may become more talkative. As serum levels increase to 5-8 mcg/mL, nystagmus, slurred speech, localized muscle twitching, or fine tremors may be noticed. Patients also have been noted to have hallucinations at these levels. If blood lidocaine levels reach 8-12 mcg/mL, focal seizure activity occurs; this can progress to generalized tonic-clonic seizures. Respiratory depression occurs at extremely high blood levels (20-25 mcg/mL) and can progress to coma.
  • If signs of CNS toxicity are noted, steps must be taken to reduce hypoxia and acidosis, because these states increase the toxicity of local anesthetics. The patient's airway should be maintained, and supplemental oxygen provided. If blood levels of carbon dioxide increase, protein binding of lidocaine decreases and results in higher levels of free lidocaine in the blood. Increased respiration and respiratory alkalosis increase the seizure threshold and decrease the uptake of the local anesthetic into the CNS. If convulsions occur, the patient's airway should be maintained, and supplemental oxygen administered. If seizure activity is sustained, 5-10 mg of diazepam should be administered slowly (1-2 mg/min) until the seizures cease.
  • Compared with the CNS, the cardiovascular system is less susceptible to the effects of local anesthetics. Most adverse effects of the cardiovascular system that occur with the administration of local anesthetics are a result of the addition of epinephrine rather than direct effects of the anesthetic. However, high blood levels of local anesthetics directly reduce cardiac contractility. In addition to the direct vasodilatory effects of most local anesthetics, the decrease in cardiac function can cause hypotension. Atrioventricular blocks, bradycardia, and ventricular arrhythmias also are reported; these are more common in patients with known conduction disturbances and requiring antiarrhythmic medications.
  • The treatment of conduction disturbances should be appropriately tailored to the type of reaction. The treatment of hypotension requires the physician to initiate advanced cardiac life support protocols, that is, he or she should ensure that the patient has a patent airway, provide supplemental oxygen, and elevate the patient's legs. If necessary, intravenous fluid should be administered, and the use of vasopressor agents such as ephedrine should be considered. Ephedrine can be intravenously administered in 5-mL incremental doses to a total of 15-30 mg, until a blood pressure response is noted.
  • Lidocaine and the FDA-approved topical anesthetics EMLA and LMX are pregnancy category B medications.

Allergic reactions

  • Allergic reactions to local anesthetics are extremely rare, especially with amide local anesthetics, and account for less than 1% of the reactions caused by local anesthetics. Reactions can be type 1 (ie, anaphylactic) or type 4 (ie, delayed-type hypersensitivity) reactions. These reactions are not dose related, but, rather, they are idiosyncratic. Skin prick and intradermal test results are negative in the vast majority of patients, but some authors recommend testing with the most commonly used amide local anesthetic (lidocaine).
  • Type 1 reactions are usually caused by ester-type anesthetics. The ester group of local anesthetics have a much greater allergenic potential than that of the amide group. Pseudocholinesterases, which produce the highly allergenic metabolic product PABA, break down ester-type anesthetics. Cross-reactivity exists among ester anesthetics; therefore, the use of all anesthetics in this structural group should be avoided in a patient with an established sensitivity to one ester-type anesthetic.
  • No cross-reactivity appears to exist between ester and amide anesthetics; however, cross-reactivity in anaphylactic reactions has not been investigated thoroughly. In addition, reactions to preservatives, specifically methylparaben and sodium metabisulfate (found in multiple-dose vials of amide anesthetics), may cause adverse reactions in a patient who is allergic to an ester-type anesthetic. Preservative-free single-dose vials of lidocaine are available for use if an amide anesthetic is to be used in a patient with a true hypersensitivity reaction to ester-type anesthetics.
  • Clinical signs of type I reactions include pruritus, urticaria, facial swelling, wheezing, dyspnea, cyanosis, laryngeal edema, nausea, vomiting, and abdominal cramping. Epinephrine with a concentration of 1:1000 should be subcutaneously administered at a dose of 0.3-0.5 mL. This dose can be repeated every 20-30 minutes to a maximum of 3 doses. If anaphylaxis ensues, a 5-mL dose of epinephrine 1:10,000 should be administered intravenously.
  • Type IV (ie, delayed-type hypersensitivity) reactions account for 80% of allergic reactions to local anesthetics. They are more common with the use of topical anesthetics and may occur with anesthetics of the amide and ester subtypes. Clinical manifestations are similar to those of allergic contact dermatitis and include erythema, plaques, and pruritus. Patients with a history of type IV reactions are not at an increased risk of type I reactions due to amide-type anesthetics. Contact dermatitis caused by topical anesthetics should be treated with topical steroid preparations.
  • Alternative agents for use as anesthetics in patients with a known allergy to both ester- and amide-type local anesthetics include isotonic sodium chloride solution and injectable antihistamines. An intradermal injection of 0.9% sodium chloride solution can provide temporary anesthesia suitable for shave or punch biopsy. Physical pressure on the nerve endings resulting from the volume injected is postulated to be responsible for the anesthetic effect. Nonbacteriostatic sodium chloride solution should be used if the patient has an allergy to the methylparaben preservative in the local anesthetic. A bacteriostatic solution, which contains benzyl alcohol, has known anesthetic properties and can be used for limited procedures such as punch biopsy.
  • Injectable antihistamines, such as diphenhydramine, have been administered to patients who are allergic to local anesthetics. The mechanism of anesthetic action is unknown. Injectable diphenhydramine is effective, but it has a short duration of activity, it is sedating, and its injection is painful. In addition, tissue necrosis is reported after the local injection of 5% diphenhydramine. If used for injection, diphenhydramine should be diluted to 1% by mixing 1 vial of 50-mg diphenhydramine with 4 mL of a bacteriostatic sodium chloride solution.

Reactions to local anesthetic additives

  • Epinephrine
    • With the exception of cocaine, local anesthetics directly cause relaxation of the vascular smooth muscle, which leads to vasodilation. This effect increases bleeding at the surgical site. Vasoconstrictors, such as epinephrine, are often added to anesthetic solutions to counteract this effect. The vasoconstrictor effect of epinephrine is maximal at 7-15 minutes, and this effect is clinically evident as blanching of the skin. This blanching also is useful in determining the area that is anesthetized.
    • Vasoconstriction not only decreases bleeding but also slows the rate of systemic absorption of the anesthetic, which allows the body more time to metabolize the anesthetic and prolongs anesthesia. Therefore, larger volumes of anesthetic can be injected when epinephrine is added to a solution. A premixed solution of lidocaine with epinephrine in a concentration of 1:100,000 (1 mg/100 mL) is available. Concentrations greater than this are associated with a higher rate of adverse effects, including an increased risk of tissue necrosis as a result of prolonged ischemia.
    • Systemic effects of epinephrine can occur with a dose as little as 2 mL of an anesthetic solution containing epinephrine in a concentration of 1:100,000. The most common clinical manifestation is transient tachycardia. At higher doses and with an inadvertent intravascular injection, palpitations, diaphoresis, angina, tremors, nervousness, and hypertension can occur. The maximum dose of epinephrine is 1 mg or 100 mL of a 1:100,000 solution. In patients with a history of heart disease, especially unstable angina and arrhythmias, the maximum dose should be decreased to 0.2 mg or 20 mL of a 1:100,000 solution (recommendation of the NY Heart Association).
    • Epinephrine is contraindicated in patients with pheochromocytoma, hyperthyroidism, severe hypertension, or severe peripheral vascular occlusive disease. Relative contraindications include pregnancy and psychological instability; epinephrine can induce an acute psychotic episode in predisposed patients.
    • The FDA designates epinephrine as a pregnancy category B medication (ie, usually safe but benefits must outweigh the risks). No known adverse effects on the fetus are reported; however, during the first trimester, vasoconstriction may cause fetoplacental ischemia and affect organogenesis. In the last trimester, epinephrine can induce premature labor if placental ischemia occurs. If possible, surgery should be performed without epinephrine, or it should be postponed until after delivery.
    • Epinephrine must be used with caution in patients taking propranolol because life-threatening reactions have been reported; these include hypertension, myocardial infarction, and stroke. Epinephrine stimulates alpha-receptors to cause vasoconstriction and increase vascular resistance. Beta-receptors balance this effect by causing vasodilation (beta2-receptors) and an increased heart rate (beta1-receptors). Like other nonselective beta-blockers, propranolol antagonizes both beta1-receptors and beta2-receptors. Therefore, in the presence of propranolol, the effects of epinephrine on alpha-receptors are unbalanced, and the result is pure alpha stimulation, which leads to severe hypertension and reflex bradycardia.
    • Although propranolol is the only nonselective beta-blocker reported to have this effect, probably all nonselective beta-blockers have the potential to cause severe hypertension and reflex bradycardia in the presence of epinephrine. A significant risk does not appear to be associated with the use of epinephrine and cardioselective beta-blockers. Although the use of epinephrine in patients who are taking nonselective beta-blockers is not contraindicated, it should be avoided if possible. Apparently, the effect may be dose related, and caution should be exercised because individual variability is reported.
    • In addition to nonselective beta-blockers, monoamine oxidase inhibitors, tricyclic antidepressants, butyrophenones, and phenothiazines can cause hypotension or hypertension in patients who are taking epinephrine.
    • Pain resulting from the infiltration of a local anesthetic can be reduced by using a solution with a pH close to physiologic range (ie, pH 7.3-7.4). The pH of plain lidocaine is 6.3-6.4. When epinephrine is added to lidocaine, the pH decreases to 3.5-4.5. The pH of the solution must be acidic to prevent the degradation of epinephrine.
  • Sodium bicarbonate
    • To reduce the pain of an injection of lidocaine and epinephrine, 1 mL of sodium bicarbonate 8.4% is added to 10 mL of the anesthetic solution to neutralize the solution. Buffered solutions should be discarded after 1 week because the effectiveness of epinephrine decreases by almost 25% during this time.
  • Hyaluronidase
    • Hyaluronidase is a bovine-derived enzyme that hydrolyzes hyaluronic acid in the connective tissue and facilitates the diffusion of the anesthetic. Although it can increase the spread of anesthesia, hyaluronidase also decreases the duration of action of the anesthetics because it increases absorption. As expected, this increased absorption leads to the potential for a greater incidence of toxic reactions that correspond to elevated blood levels. To decrease distortion of the surgical site, the addition of hyaluronidase is useful for nerve blocks and procedures around the orbit.
    • Hyaluronidase is marketed in ampules. One ampule is equivalent to 150 United States Pharmacopeia (USP) units per milliliter. The usual dilution is 150 U in 30 mL of anesthetic. A patient can have an allergy to hyaluronidase. Hyaluronidase is a foreign protein, and its use is contraindicated in patients with a known allergy to bee stings. In addition, hyaluronidase contains the preservative thimerosal, which is a known allergen. To evaluate the potential for an allergic reaction before infiltration, a test dose should be injected intradermally. If urticaria is observed at the site of the test injection, the use of hyaluronidase is contraindicated.
Source Emedicine.medscape.com

 

Thứ hai, 13 Tháng 9 2010 15:28

Trigger Point Injection for Pain Management

Written by

Trigger point injection (TPI) may be an option in treating pain for some patients. TPI is a procedure used to treat painful areas of muscle that contain trigger points, or knots of muscle that form when muscles do not relax. Many times, such knots can be felt under the skin. Trigger points may irritate the nerves around them and cause referred pain, or pain that is felt in another part of the body.

What Happens During Trigger Point Injection?

In the TPI procedure, a health care professional inserts a small needle into the patient's trigger point. The injection contains a local anesthetic that sometimes includes a corticosteroid. With the injection, the trigger point is made inactive and the pain is alleviated. Usually, a brief course of treatment will result in sustained relief. Injections are given in a doctor's office and usually take just a few minutes. Several sites may be injected in one visit. If a patient has an allergy to a certain medication, a dry-needle technique (involving no medications) can be used.

When Is Trigger Point Injection Used?

TPI is used to treat many muscle groups, especially those in the arms, legs, lower back, and neck. In addition, TPI can be used to treat fibromyalgia and tension headaches. TPI also is used to alleviate myofascial pain syndrome (chronic pain involving tissue that surrounds muscle) that does not respond to other treatments. However, the effectiveness of TPI for treating myofascial pain is still under study.

Source American Family Physician

Latest Items

Chính sách bảo mật

Hits:64 Chính sách & Hướng dẫn BS Mai Trung Dũng

Cám ơn quý khách đã truy cập vào website Điều Trị Đau Shop được vận hành bởi CÔNG TY CỔ PHẦN PHÁT TRIỂN KHOA HỌC KỸ THUẬT Y SINH - BIOMEDICAL TECH. Chúng tôi tôn trọng và cam kết sẽ...

Read more