Nerve root blockade is useful in diagnosing and treating pain present in a dermatomal distribution.
After informed consent is obtained, the patient is placed in the prone position, and a line perpendicular to the axis of the spine is drawn across the top of the spinous process. In the lumbar region, a line drawn along the inferior edges of the two transverse processes will intersect the spinous process of the same vertebra at its most cephalad point. In the thoracic region, this line can extend as much as two vertebral levels caudally, particularly in the midthoracic region. The patient is prepared in a standard aseptic fashion over an area large enough to allow palpation of landmarks, and strict sterile technique is used throughout the procedure. A 4-in. (10-cm), 22-gauge needle is inserted 3 to 5 cm laterally from the midline, which should overlie the transverse process. The needle is advanced perpendicular to the skin until contact is made with the transverse process. The depth is noted at this point. The needle is pulled back to skin level and redirected to pass below the transverse process. Appropriate response with a nerve stimulator or paresthesia indicates correct placement. After negative aspiration, 2 to 5 mL of local anesthetic is injected to block the spinal nerve root (Fig. 67-7).
FIGURE 67-7. Spinal nerve root block. A: Fluoroscopic view for L5 nerve root block (arrow). B: Approach for spinal nerve root injection and neural blockade.
The technique of nerve root blockade is similar to that of the intercostal block. The transverse process serves as the depth marker for nerve roots. A sound knowledge of the relationship of the transverse process and the spinous process is necessary to locate precisely the selected nerve root. Any disorder that responds to intercostal blockade also should respond to selective nerve root blockade.
Complications usually occur from injection of local anesthetic agents into areas adjacent to the paravertebral space such as the epidural or subarachnoid space. Puncture of retroperitoneal organs and bleed also can occur if care is not taken to consider the anatomy fully.