Overview of the introduction of neuromuscular monitoring to clinical anaesthesia.

Muscle relaxants were introduced into clinical practice in the early 1940s. From 1949, assessments were being made of the efficacy of various agents in awake volunteers, usually the researchers themselves. From the early to mid 1950s, while interest in using muscle relaxants was keen, concern emerged in the surgical literature that there was a higher mortality rate seen in patients receiving muscle relaxants. In fairness, the major article highlighted lack of randomisation, bias and confounding variables but this was largely regarded as showing a toxicity associated with muscle relaxants. By 1961 the matter had been settled that muscle relaxants were not toxic but required careful management and administration. Perhaps fortuitously, measurement of the degree of muscle relaxation was introduced to clinical practice with the use of nerve stimulation. These were measured responses to single twitch stimulus or tetanic stimulation. In 1970, train-of-four ratio was introduced, then in 1981 post-tetanic count, and in 1989 double burst stimulation. This article reviews the introduction of these techniques.