The effect of hypothermia on isoflurane MAC in children.

BACKGROUND Hypothermia has been shown to decrease the requirement for inhaled anesthetics in animals, but information in humans is limited. METHODS Thirty-three unpremedicated children with congenital left-to-right shunt heart diseases undergoing open heart surgeries were assigned to one of three groups, with nasopharyngeal temperatures at the time of skin incision of 37, 34, or 31 degrees C. Anesthesia was induced and maintained with isoflurane in oxygen. End-tidal isoflurane concentration and nasopharyngeal temperature were kept at stable levels for at least 15 min before the skin incision. Isoflurane minimum alveolar concentration was determined by using the Dixon up-and-down approach. RESULTS Isoflurane minimum alveolar concentration values were 1.69 +/- 0.14%, 1.47 +/- 0.10%, and 1.22 +/- 0.15% (mean +/- SD) at 37, 34, and 31 degrees C, respectively. CONCLUSIONS Hypothermia decreases the isoflurane requirement in children by 5.1 degrees C.