Conduction Blocks and Spinal Anesthesia
There are many types of conduction blocks, depending on the nerve groups affected by the injection. Epidural anesthesia is achieved by injecting a local anesthetic into the spinal canal in the space surrounding the dura mater . Epidural anesthesia also blocks sensory, motor, and autonomic functions, but it is differentiated from spinal anesthesia by the injection site and the amount of anesthetic used.
Epidural doses are much higher because the epidural anesthetic does not make direct contact with the cord or nerve roots. An advantage of epidural anesthesia is the absence of headache that occasionally results from subarachnoid injection. A disadvantage is the greater technical challenge of introducing the anesthetic into the epidural rather than the subarachnoid space. If inadvertent subarachnoid injection occurs during epidural anesthesia and the anesthetic travels toward the head, high spinal anesthesia can result; this can produce severe hypotension and respiratory depression and arrest. Treatment of these complications includes airway support, intravenous fluids, and use of vasopressors. Other types of nerve blocks include:
- Brachial plexus block, which produces anesthesia of the arm
- Paravertebral anesthesia, which produces anesthesia of the nerves supplying the chest, abdominal wall, and extremities
- Transsacral (caudal) block, which produces anesthesia of the perineum and, occasionally, the lower abdomen
Spinal anesthesia is a type of extensive conduction nerve block that is produced when a local anesthetic is introduced into the subarachnoid space at the lumbar level, usually between L4 and L5 (see Fig. 19-2). It produces anesthesia of the lower extremities, perineum, and lower abdomen.