Use of the peripheral nerve stimulator.

The author discusses various procedures for assessing the patient's degree of muscle relaxation utilizing a peripheral nerve stimulator. Based on clinical observation, a preferred method is offered. To obtain the relaxation necessary for certain surgical procedures, the usual technique is to administer a pre-calculated dose of non-depolarizing muscle relaxant. The most common method to calculate the correct dosage is to multiply the patient's weight by an average recommended figure that varies from one relaxant to another. Although this method generally produces satisfactory relaxation, we have seen cases where more relaxation was required , making additions to the calculated dose necessary. Conversely, we have seen cases that were extremely difficult or even impossible to reverse upon termination of surgery. In most cases, this suggests that too much muscle relaxant was given. This situation was particularly prevalent when Pavulon® was first introduced into this country; many practitioners relied upon the upper end of the dosage scale to produce relaxation in their patients. These incidences clearly demonstrate that the calculated dose method of giving muscle relaxants, although adequate in the average situation, is little more than an educated guess. With the many variants that come into play with each individual patient, it is evident that a simple, reliable method of titrating muscle relaxants would give a more exacting, accurate anesthetic dosage, and remove some of the guesswork from our task. Such a method would increase the margin of safety of the 152 anesthetic. The peripheral nerve stimulator, already available on the market, provides this method. Investigations involving the use of this instrument have pointed to other factors that, when properly utilized, also add to the margin of safety. It has been the practice of many anesthetists to avoid reversing non-depolarizing muscle relaxants at the end of the procedure if the patient demonstrated what seemed to be an adequate tidal volume. This philosophy seemed reasonable until 1967 when Paton and Waud showed that a muscle could be made to contract fully with only 20-25% of the receptors in the muscle available for use.' When applied to the respiratory muscles, a patient could conceivably have an adequate tidal volume but still be 75-80% paralyzed. This implies that patients have a very small margin of safety available to them should something occur requiring them to exert more strength than the partially recovered respiratory muscles could manage. An obstructed airway momentarily unnoticed in a busy recovery room, …