Monitoring and reversal of neuromuscular block.

Abstract

Methods of monitoring and reversing neuromuscular blocking agents to avoid residual neuromuscular block are described. Studies have shown that if a long-acting neuromuscular blocking agent is used during anesthesia, the frequency of residual block, regardless of the method of neuromuscular monitoring, will be at least 20%. In the past 20-25 years, anesthesiologists have come to use some form of nerve stimulation to monitor the degree of residual neuromuscular block; there are various patterns of stimulation, including train-of-four (TOF) stimulation and double-burst stimulation (DBS). For both TOF stimulation and DBS, the response to the stimuli in a series fades such that the last response can be expressed as a ratio of the first. The fade to DBS is the same as that to TOF stimulation. Clinicians can clinically detect a fade in TOF response when the TOF ratio is <0.5. Fade to DBS is easier to detect than that to TOF stimulation, but, as the block recovers, the anesthesiologist's ability to detect fade decreases. Although anesthesiologists have accepted a TOF ratio of at least 0.7 as the standard, studies of vecuronium neuromuscular block have shown an impaired ventilatory response to hypoxemia and the possibility of increased risk of aspiration until the TOF ratio recovered to 0.9. The use of pancuronium and a persistent TOF ratio of 0.7 in the postanesthesia care unit was shown to be associated with a threefold greater occurrence of postoperative pulmonary complications compared with vecuronium or atracurium. Spontaneous recovery from neuromuscular block occurs through redistribution, metabolism, or buffered diffusion, but recovery can be accelerated by administration of anticholinesterase agents, such as neostigmine and edrophonium. Studies suggest that even intermediate-duration agents should be reversed. Rapacuronium is a new investigational drug with similar onset characteristics to succinylcholine and, if reversed early, similar recovery characteristics. Postoperative residual neuromuscular block is frequent, dangerous, and difficult to recognize clinically. The action of neuromuscular blocking agents should always be reversed unless there is unequivocal evidence of adequate function.