Effects of small peripheral temperature changes on the evoked baseline electromyographic response

Since muscle temperature seems to influence the electrically evoked compound muscle action potentials, we wanted to quantificate the effect of light external cooling and warming on evoked responses in a clinical setting.

In ophthalmic surgical patients (ASA I-III), evoked electromyographic (EMG) responses to supramaximal train-of-four stimuli were measured once a minute. After obtaining an initial baseline (100%) where temperatures of the first dorsal interosseal muscle and the skin above it had stabilised, the patients' hands were cooled to stable temperatures by a blower (room air). A new baseline was established and, subsequently, the hand re-warmed to the starting temperature. The cooling procedure was repeated, operation time allowing.

The mean (range) muscle and skin temperature changes were from 36.0 degrees C (35.5-37.1) to 34.6 degrees C (33.2-36.1) and 35.7 degrees C (35.0-36.7) to 32.0 degrees C (29.4-35.6), respectively. The mean (range) change of the EMG-response was 8.0%/degree C (0.3-16.5) for the muscle and 4.1%/degree C (0.3-37.9) for the skin. Wide individual variability was evident.

The electrically evoked EMG-response is sensitive to even small changes in temperature at the measurement site. Therefore, when applying the evoked EMG in neuromuscular studies, peripheral skin or muscle temperatures need to be monitored, and attempts to stabilise the temperature of the monitored muscles should be made.