Regional Nerve Block

A regional nerve block is an injection of local anaesthetic around a peripheral nerve or a nerve plexus, interrupting conduction so that everything distal to the injection loses sensation. The drugs block voltage-gated sodium channels in the axon membrane, so the impulse fails to propagate. Ultrasound guidance has largely replaced landmark and paraesthesia techniques for placement.

Blocks are named for the target: interscalene, supraclavicular and axillary approaches to the brachial plexus for the upper limb; femoral, adductor canal and popliteal sciatic for the lower. Agents differ in kinetics — lidocaine has fast onset and a few hours of duration, while bupivacaine and ropivacaine take longer to set up and can last twelve to twenty-four hours. Duration varies with dose, site, adjuncts and the individual, which is one reason clearance and Xenobiotic Metabolism matter to dosing limits.

The characteristic hazard is not the block but its end. A dense block means zero Nociception reaching awareness, so the region feels normal while tissue injury and surgical trauma proceed unfelt. When conduction returns, often abruptly and often overnight, pain arrives at full intensity with no ramp — the rebound cliff. The contrast with the preceding numbness makes it worse than the same pain would otherwise seem, a straightforward Anchoring Effect.

The countermeasure is planning around the cliff rather than reacting to it: start non-opioid analgesia on a fixed schedule before sensation returns, so levels are established when the block regresses, and reserve stronger agents for the peak. Multimodal regimens reduce total opioid exposure, which bears on Physical Dependence, and they pair naturally with the operative work described in Fracture Fixation.