Background: Patients may require perioperative cooling for a variety of reasons including treatment of a malignant hyperthermia crisis and induction of therapeutic hypothermia for neurosurgery. The authors compared heat transfer and core cooling rates with five cooling methods.
Methods: Six healthy volunteers were anesthetized with desflurane and nitrous oxide. The cooling methods were 1) circulating water (5 degrees C, full-length mattress and cover), 2) forced air (10 degrees C, full-length cover), 3) gastric lavage (500 ml iced water every 10 min), 4) bladder lavage (300 ml iced Ringer's solution every 10 min), and 5) ice-water immersion. Each method was applied for 40 min or until the volunteers' core temperatures approached 34 degrees C. The volunteers were rewarmed to normothermia between treatments. Core cooling rates were evaluated using linear regression.
Results: The first volunteer developed abdominal cramping and diarrhea after gastric lavage. Consequently, the technique was not again attempted. Bladder lavage increased heat loss approximately 10 W and decreased core temperature 0.8 +/- 0.3 degrees C/h (r2 = 0.99 +/- 0.002; means +/- SD). Forced-air and circulating-water cooling comparably increased heat flux, approximately 170 W. Consequently, core cooling rates were similar during the two treatments at 1.7 +/- 0.5 degrees C/h (r2 = 0.99 +/- 0.001) and 1.6 +/- 1.1 degrees C/h (r2 = 0.98 +/- 0.02), respectively. Immersion in an ice water slurry increased heat loss approximately 600-800 W and decreased core temperature 9.7 +/- 4.4 degrees C/h (r2 = 0.98 +/- 0.01). Immersion cooling was associated with an afterdrop of approximately 2 degrees C.
Conclusions: Bladder lavage provided only trivial cooling and gastric lavage provoked complications. Forced-air and circulating-water cooling transferred relatively little heat but are noninvasive and easy to implement. Forced-air or circulating-water cooling, perhaps combined with intravenous administration of refrigerated fluids, may be sufficient in some patients. When noninvasive methods prove insufficient for rapid cooling, ice-water immersion or peritoneal lavage probably should be the next lines of defense.