Influence of muscle temperature and forearm position on evoked electromyography in the hand

We have examined the correlation between the evoked electromyographic response in the first dorsal interosseous muscle of the hand, temperature and forearm position in 40 female patients after enflurane anaesthesia with spontaneous breathing. In 20 patients the supinated forearm with the wrist extended was immobilized on an armboard with adhesive tape (group A). In the other 20 patients (group B), the hand was strapped into a fist with adhesive tape and laid supine on an armboard. During the 30 min after induction of anaesthesia, the mean response to the first stimulus in the train-of-four was the same in both groups and decreased from a baseline value of 99.7% (95% confidence interval (CI) 99.1-100.4%) to 86.2% (95% CI 83.3-89.0%). The final response was less than 90% of baseline in 28 patients. There was an inverse linear correlation between the electromyographic response and both skin and muscle temperature in both groups (r > 0.98), although there was no correlation between change in the electromyogram and change in temperature (r < -0.26). After 30 min, pronation of the forearm resulted in a further decrease in the electromyographic response in 13 of 18 patients in group B (two patients in this group were excluded from analysis). Pressure was then applied to the scaphoid tubercles of all patients to produce maximal supination of the forearm. This had no effect on the electromyogram in 10 patients. In 28 patients the electromyographic response increased after scaphoid pressure, although it remained 90% of baseline in five patients. The measured temperatures did not alter during these manoeuvres.