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Diagnostic & Therapeutic Blocks
Local anesthetic nerve blocks are useful in delineat-ing pain mechanisms, and they play a major role in the management of patients with acute or chronic pain. Pain relief following diagnostic nerve blockade often carries favorable prognostic implications for a subsequent therapeutic series of blocks. Although the utility of differential nerve blocks in distinguish-ing between somatic and sympathetic mechanisms has been questioned, this technique can identify patients exhibiting a placebo response and those with psychogenic mechanisms. In selected patients, “per-manent” neurolytic nerve blocks may be appropriate.
The efficacy of nerve blocks is presumably due to interruption of afferent nociceptive activity. This is in addition to, or in combination with, blockade of afferent and efferent limbs of abnormal reflex activ-ity involving sympathetic nerve fibers and skeletal muscle innervation. The pain relief frequently out-lasts (by hours up to several weeks) the known pharmacological duration of the agent employed. Selection of the type of block depends on the loca-tion of pain, its presumed mechanism, and the skills of the treating physician. Local anesthetic solutions may be applied locally (infiltration), or at a specific peripheral nerve, somatic plexus, sympathetic gan-glia, or nerve root. The local anesthetic may also be applied centrally in the neuraxis.
The use of ultrasound in interventional pain medi-cine has increased over the past decade due to its utility in visualizing vascular, neural, and other ana-tomic structures; its role as an alternative to the use of fluoroscopy and iodine-based contrast agents; and progressive improvements in technology lead-ing to better visual images and greater simplicity of use. Most notably, ultrasound has become very useful for visualizing blood vessels and potentially decreasing the incidence of intravascular injection of particulate steroid medications. It may also be helpful in decreasing the risk of pneumothorax and of intraperitoneal injection. Procedures that may benefit from ultrasound guidance include trigger point injections, nerve blocks, and joint injections.
Fluoroscopy is frequently used for interventional pain procedures. It is highly effective for visualizing bony structures and observing the spread of radiopaque contrast agents. Live fluoroscopy with contrast agent should be used to minimize the risk of intravascular injection of therapeutic agents. Care should be taken to avoid excessive use of fluoroscopy and to employ appropriate radiation shielding, given the risks of ionizing radiation to the patient and to the health care team members in the fluoroscopy suite.
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