Use of a Peripheral Nerve Stimulator During Surgery

If tracheal intubation is facilitated by the administration of succinylcholine, no more muscle relaxant should be given until the response to nerve stimulation reappears or until the patient shows other signs of returning neuromuscular function. If the plasma cholinesterase

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Figure 39-20 This diagram shows when the different modes of electrical nerve stimulation can be used during clinical anesthesia. Dark areas indicate appropriate use; light areas, less effective use. Modes of nerve stimulation: TOF, train-of-four stimulation; PTC, post-tetanic count; DBS, double-burst stimulation; and ?, indicating that TOF is less useful in the recovery room unless measured using mechano-, electro-, or acceleromyography. (See text for further explanation.)

When a nondepolarizing neuromuscular drug is used for tracheal intubation, a longer-lasting period of intense blockade usually follows. During this period of no response to TOF and single-twitch stimulation, the time until return of response to TOF stimulation may be evaluated by using post-tetanic count (see Fig. 39-5 ).

For most surgical procedures requiring muscle relaxation, a twitch depression of approximately 90% will be sufficient, provided the patient is properly anesthetized. If a nondepolarizing relaxant is used, one or two of the responses to TOF stimulation can be felt. However, because the respiratory muscles (including the diaphragm) are less sensitive to neuromuscular blocking agents than are the peripheral muscles, the patient may breathe, hiccup, or even cough at this depth of block. To ensure paralysis of the diaphragm, neuromuscular blockade of the peripheral muscles must be so intense that PTC stimulation is zero in the thumb.

An added advantage of keeping the neuromuscular blockade at a level of one or two responses to TOF stimulation is that antagonism of the block is facilitated at the end of surgery.