Monitoring of neuromuscular function

Monitoring neuromuscular transmission provides valuable information to the anesthesiologist. The acquisition of relevant data contributes to a more predictable and rational approach to the use of muscle relaxants and assures improved patient care during and in the immediate postoperative period. Clinical noninvasive criteria such as the presence or absence of diplopia and or ptosis, the ability to open the eyes widely, protrude the tongue or swallow, measurement of hand grip strength or head lift or assessment of the vital capacity are limited to awake and cooperative patients. Measurement of inspiratory force and tidal volume can be evaluated in anesthetized patients breathing spontaneously. Central depressant drugs tend to depress these respiratory parameters. Accordingly, the assumption that relaxants are responsible for respiratory depression at the end of an anesthetic can only be documented when impairment of neuromuscular transmission can be demonstrated. The most reliable method of measuring neuromuscular function is to stimulate an accessible peripheral motor nerve and measurement of the evoked response of the skeletal muscle or muscles innervated by the stimulated motor nerve. The evoked muscle response depends on the pattern of motor nerve stimulation: Single twitch stimuli at a defined frequency, tetanic stimulation, posttetanic single twitch stimulation or train-of-four stimulation. The response to these different modes of stimulation can be assessed either mechanically (evoked tension response) or electrically (evoked electromyography: EMG or integrated EMG). These response criteria can be employed either individually or combined to evaluate the response to muscle relaxants and to assess the adequacy of recovery from neuromuscular blockade.