The Effectiveness of Rapidly Infused Intravenous Fluids for Inducing Moderate Hypothermia in Neurosurgical Patients

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Abstract
Moderate hypothermia is often used for cerebral pro- tection during anesthesia for cerebral aneurysm clip- ping. No reliable, rapid, and practical noncardiopulmo- nary bypass methods for the induction of hypothermia to core temperatures ,34°C have been reported. We assessed the effects of IV administration of chilled 5% albumin (5 mL/kg at 1- 6°C) on core temperature after surface cooling to approximately 34°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 6 0.1°C. The same volume of chilled albumin infused over 30 min reduced core temperature by 0.4 6 0.1°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 to- tal 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 adminis- tered very rapidly (.100 mL/min) to avoid heat gains in standard IV tubing that occur even with rapid ad- ministration. Implications: Chilled IV fluids can be much more effective for the induction of hypothermia than commonly assumed, but they must be adminis- tered very rapidly to avoid heat gains in IV tubing. (Anesth Analg 1999;89:163-9)