DO STANDARD MONITORING SITES REFLECT TRUE BRAIN TEMPERATURE WHEN PROFOUND HYPOTHERMIA IS RAPIDLY INDUCED AND REVERSED

Background: Brain temperature is closely approximated by most body tem perature measurements under normal anesthetic conditions. However, whe n thermal autoregulation is overridden, large temperature gradients ma y prevail. This study sought to determine which of the standard temper ature monitoring sites best approximates brain temperature when deep h ypothermia is rapidly induced and reversed during cardiopulmonary bypa ss. Methods: Twenty-seven patients underwent cardiopulmonary bypass an d deep hypothermic circulatory arrest in order for each to have a gian t cerebral aneurysm surgically clipped, Brain temperatures were measur ed directly with a thermocouple embedded in the cerebral cortex. Eight other body temperatures were monitored simultaneously with less invas ive sensors at standard sites, Results: Brain temperature decreased fr om 32.6 +/- 1.4 degrees C (mean +/- SD) to 16.7 +/- 1.7 degrees C in 2 8 +/- 7 min, for an average cerebral cooling rate of 0.53 +/- 0.15 deg rees C/min. Circulatory arrest lasted 24 +/- 15 min and was followed b y 63 +/- 17 min of rewarming at 0.31 +/- 0.09 degrees C/min, None of t he monitored sites tracked cerebral temperature well throughout the en tire hypothermic period, During rapid temperature change, nasopharynge al, esophageal, and pulmonary artery temperatures corresponded to brai n temperature with smaller mean differences than did those of the tymp anic membrane, bladder, rectum, axilla, and sole of the foot, At circu latory arrest, nasopharyngeal, esophageal, and pulmonary artery mean t emperatures were within 1 degrees C of brain temperature, even though individual patients frequently exhibited disparate values at those sit es. Conclusions: When profound hypothermia is rapidly induced and reve rsed, temperature measurements made at standard monitoring sites may n ot reflect cerebral temperature, Measurements from the nasopharynx, es ophagus, and pulmonary artery tend to match brain temperature best but only with an array of data can one feel comfortable disregarding disc ordant readings.