The relationship between adductor pollicis twitch tension and core, skin, and muscle temperature during nitrous oxide-isoflurane anesthesia in humans.

Temperature and volatile anesthetic agents influence neuromuscular transmission. Because mild hypothermia is common during general anesthesia, the authors sought to determine the relationship between the core temperature, adductor pollicis muscle temperature, and the twitch response of the adductor pollicis muscle, during isoflurane anesthesia in 15 patients undergoing elective surgery in which muscle relaxants were not required. Five patients were allowed to cool spontaneously, five were cooled actively, and normothermia was maintained actively in the remaining five. In the normothermic patients (core greater than 36.5 degrees C, muscle greater than 35.7 degrees C), the twitch response of the muscle remained unchanged from control values. In the patients who were cooled passively or actively, a muscle temperature threshold was observed (35.2 degrees C), below which twitch response of the muscle diminished by 10-15%/degrees C decrease in muscle temperature. To ensure that the adductor pollicis muscle temperature remained above 35.2 degrees C, the core temperature had to be maintained above 36 degrees C. A significant linear relationship (P less than 0.05) was found between the adductor pollicis muscle temperature and twitch tension below the threshold for each individual patient in the cooled groups (correlation coefficient range, 0.80-0.99). Thus, there is a temperature-related decrease in adductor pollicis twitch response during isoflurane anesthesia, and the temperature of this muscle should be maintained above 35-35.5 degrees C during studies of neuromuscular transmission. This can be achieved by maintaining core temperature above 36 degrees C.