The effectiveness of rapidly infused intravenous fluids for inducing moderate hypothermia in neurosurgical patients

Moderate hypothermia is often used for cerebral protection during anesthesia for cerebral aneurysm clipping. No reliable, rapid, and practical noncardiopulmonary bypass methods for the induction of hypothermia to core temperatures <34 degrees C have been reported. We assessed the effects of TV administration of chilled 5% albumin (5 mL/kg at 1-6 degrees C) on core temperature after surface cooling to approximately 34 degrees C. We calculated thermal distribution volume from the change in core temperature after the chilled fluid infusions. We also compared rapid administration (5 mL/kg over 30 min) with very rapid administration (5 mL/kg over 3-5 min). Chilled albumin 5 mL/kg infused over 5 min reduced core temperature by 0.6 +/- 0.1 degrees C. The same volume of chilled albumin infused over 30 min reduced core temperature by 0.4 +/- 0.1 degrees C. The calculated thermal distribution volume was less than one third of total body volume. Because the thermal distribution volume in these hypothermic patients was much lower than total body volume, the chilled IV fluids in this study were 3 times more effective in inducing hypothermia than suggested by a simple calculation. To achieve maximal effectiveness, however, chilled fluids must be administered very rapidly (>100 mL/min) to avoid heat gains in standard TV tubing that occur even with rapid administration. Implications: Chilled TV fluids can be much more effective for the induction of hypothermia than commonly assumed, but they must be administered very rapidly to avoid heat gains in IV tubing.