When pain is refractory to pharmacologic treatment, peripheral nerve blockade may be an option (Raj 1996). Somatic nerve blocks are used in patients with intractable pain, generally from cancerous invasion of parts of the body, including the nervous system. At times, these blocks are employed in peripheral nerve pain, sciatica, and carpal tunnel syndrome. In addition, peripheral nerve blocks are employed to provide analgesia during localized surgery so that the patient can avoid general anesthesia.
Nerve blocks can include anesthetic and ablative modalities (see Table 7-4). In the case of anesthetic blockade, introduction of local anesthetics (lidocaine or bupivacaine) allows for interruption of pain transmission, producing effective, albeit temporary, pain relief. The activity of thin and unmyelinated nerve fibers (e.g., AS and C fibers) is particularly prone to inhibition, requiring minimal doses of anesthetic agents. If higher doses are used, it is possible to inhibit larger myelinated fibers, such as motor neurons. Pain interruption might be of sufficient duration to allow the patient to become more proactive with physical therapy, which in turn might set the stage for further health improvements and rehabilitation. Ablative techniques involve application of ethanol or phenol or other interventions (see Table 7-4) that result in permanent destruction of the nerve. Neural destruction is never attempted unless local application of anesthetics has first been tried. If local anesthetics fail to produce pain relief, it is unlikely that neural destruction will be effective in mitigating pain.
Anesthetic infusions can produce untoward effects (e.g., hypotension, localized numbness, muscle weakness, infection, bleeding). Such measures should never be attempted unless resuscitation equipment is readily available.
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