Local anesthetic nerve block

Local anesthetic nerve block (local anesthetic regional nerve blockade, or often simply nerve block) is a short-term nerve block, usually lasting hours or days, involving the injection of an anesthetic, a corticosteroid and other agents onto or near a nerve, usually for pain relief or anesthesia.

A combination of local anesthetic (such as lidocaine), epinephrine, a steroid (corticosteroid), and an opioid is often used. Epinephrine induces constriction of the blood vessels which delays the diffusion of the anesthetic. Steroids can help to reduce inflammation. Opioids are painkillers. These blocks can be either single treatments, multiple injections over a period of time, or continuous infusions. A continuous peripheral nerve block can be introduced into a limb undergoing surgery; for example, a femoral nerve block to prevent pain in knee replacement.

Local anesthetic nerve blocks are sterile procedures that are usually performed in an outpatient facility or hospital. The procedure can be performed with the help of ultrasound, fluoroscopy (a live X-ray), or CT. Use of any one of these imaging modalities enables the physician to view the placement of the needle. A probe positioning system can be used to hold the ultrasound transducer steady. Electrical stimulation can provide feedback on the proximity of the needle to the target nerve.

Local anesthetic nerve blocks act on the voltage-gated sodium channels that conduct electrical impulses and mediate fast depolarization along nerves. These channels are the target of local anesthetics (LA). LA target open channels, bind on the inner side of the nerve membrane, and prevent ion flow. LA often contain a tertiary amine group. Both the protonated and neutral forms lessen the membrane permeability of the nerve to sodium. Recently, studies have implicated that multiple S6 segments form the LA binding site within the channel. S6 segments are transmembrane helices within the channel protein. There are four homologous repeats in the channel protein with segments labeled S1-S6 indicating the 6 transmembrane α-helices. Thus, in total, there are four S6 segments. S6 segments in particular are implicated in formation of the inner pore. Additionally, open or inactivated sodium channels produce a higher binding affinity than resting states due to conformational change during gating. Dissociation of LA occurs only from open channels.

...
Wikipedia