Because we use neuromuscular blocking agents (muscle relaxants, for short) so frequently, we need to monitor the degree of relaxation. Clinical judgment goes a long way, but instruments can gauge the degree of relaxation and provide numer-ical assessment. For this purpose, we use a nerve stimulator that delivers short pulses of a direct current. We use two stick-on electrodes placed fairly close together (Fig. 7.3) over the course of a nerve (usually the ulnar nerve close to the wrist), and select one of several patterns of stimuli. Ideally, the current is well below the level to stimulate the muscle directly, as a healthy muscle will respond to strong, direct stimulation even in the presence of neuromuscular blocking agents. Thus, we are looking for maximal stimulation of the nerve only. Submax-imal stimulation of the nerve can induce variability of response and thus make it impossible to tell whether an observed depression must be attributed to neuro-muscular blockade or inadequate stimulation.
The most commonly used patterns of stimulation are shown in Table 7.2, with the typical patterns of response depicted in Fig. 7.4. In addition to the response to nerve stimulation, we like to check the patient’s muscle power if possible. Full return of muscle power can be assumed if the patient can lift his head off the pillow for 5 seconds, or bite on a tongue depressor so that you cannot withdraw it. If we suspect residual neuromuscular blockade in the PACU, we ask if the patient has double vision or difficulty sitting up or swallowing.