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