Monitoring during peripheral nerve blockade

Abstract

Objective monitors to warn against adverse events specific to the performance of nerve blockade are relatively unsophisticated compared with monitors used during general anesthesia. The purpose of this review is to outline the various monitors available, and how they can be used to reduce nerve block-related complications. Evidence is accumulating for three objective means of preventing complications. Electrical nerve stimulation is insensitive, but specific, at detecting intraneural needle placement, such that if a motor response is obtained with a current of 0.2 mA or less, the needle tip is positioned intraneurally. Ultrasonography allows for reduction of the volume of local anesthetic required to accomplish a nerve block, reducing the potential for systemic toxicity. The value of ultrasound in reducing inadvertent puncture of neighboring structures, while intuitive, is less clear. Finally, injection pressure monitoring helps objectively distinguish between an injection into low versus high compliance tissue (e.g. intrafascicular versus extrafascicular). Peripheral nerve blockade has evolved from an entirely blind procedure to a more reproducible subspecialty. Several monitors exist to objectively guide and monitor needle placement and application of local anesthetics. Because these monitors are complementary, best practice may involve combining all of these monitoring options when performing peripheral nerve blocks.