WHEN TO USE A PERIPHERAL NERVE STIMULATOR

At some institutions, nerve stimulators are used routinely whenever a neuromuscular blocking drug is given. In most cases, the response is evaluated by touch, and only in selected cases are the responses recorded. Many anesthesiologists do not agree with an extensive use of nerve stimulators and argue that they manage quite well without

TABLE 39-3 -- Clinical tests of postoperative neuromuscular recovery

Unreliable

Sustained eye opening

Protrusion of the tongue

Arm lift to opposite shoulder

Normal tidal volume

Normal or near normal vital capacity

Maximum inspiratory pressure <40–50 cm H2 O

Reliable

Sustained head-lift for 5 seconds

Sustained leg lift for 5 seconds

Sustained hand grip for 5 seconds

Sustained "tongue depressor test"

Maximum inspiratory pressure ≥40–50 cm H2 O

(Normal swallowing?)

1566

In daily clinical practice significant residual block can be excluded with certainty only if objective methods of neuromuscular monitoring are used.^{[77] [78]} In my opinion^[5] and those of others,^[6] good evidence-based practice dictates that clinicians should always quantitate the extent of neuromuscular recovery using objective monitoring. At a minimum, the TOF ratio should be measured during recovery whenever a non-depolarizing neuromuscular block is not antagonized.^[5]

However, in many departments clinicians do not have access to equipment for measuring the degree of block. How then to evaluate and, as far as possible, exclude clinically significant postoperative block? First, long-acting neuromuscular blocking agents should not be used. Second, the tactile response to TOF nerve stimulation should be evaluated during surgery. Third, avoid if possible total twitch suppression. Keep the block so that there is always one or two tactile TOF responses. Fourth, the block should be antagonized at the end of the procedure, but reversal should not be initiated before at least two and preferably three or four responses to TOF stimulation are present. Fifth, during recovery, tactile evaluation of the response to DBS is preferable to tactile evaluation of the response to TOF stimulation, because it is easier to feel fade in the DBS than in the TOF response. Sixth, recognize that absence of tactile fade in both the TOF and the DBS responses does not exclude significant residual block.^{[33] [103] [104] [110]} Finally, reliable clinical signs and symptoms of residual block (see Table 39-3 ) should be considered in relation to the response to nerve stimulation.

Considering the uncertainty connected with both the use of clinical tests of postoperative neuromuscular recovery and tactile evaluation of the response to nerve stimulation, at a minimum every anesthesia department and every recovery room should have at least one apparatus for recording evoked responses. Whether the functioning of such a neuromuscular transmission analyzer is based on EMG, MMG, AMG, P_Z EMG or PMG is not crucial, as long as the physician knows how to use the apparatus in question.