Core cooling by central venous infusion of ice-cold (4 degrees C and 20 degrees C) fluid - Isolation of core and peripheral thermal compartments

Background: Central venous infusion of cold fluid may be a useful method of inducing therapeutic hypothermia. The aim of this study was to quantify sy stemic heat balance and regional distribution of body heat during and after central infusion of cold fluid. Methods: The authors studied nine volunteers, each on two separate days. An esthesia was maintained with use of isoflurane, and on each day 40 ml/kg sa line was infused centrally over 30 min. On one day, the fluid was 20 degree s C and on the other It was 4 degrees C. By use of a tympanic membrane prob e core (trunk and head) temperature and heat content were evaluated. Periph eral compartment (arm and leg) temperature and heat content were estimated with use of fourth-order regressions and integration over volume from 18 in tramuscular thermocouples, nine skin temperatures, and "deep" hand and foot temperature. Oxygen consumption and cutaneous heat flux estimated systemic heat balance. Results: After 30-min infusion of 4 degrees C or 20 degrees C fluid, core t emperature decreased 2.5 +/- 0.4 degrees C and 1.4 +/- 0.2 degrees C, respe ctively. This reduction in core temperature was 0.8 degrees C and 0.4 degre es C more than would be expected if the change in body heat content were di stributed in proportion to body mass. Reduced core temperature resulted fro m three factors: (1) 10-20% because cutaneous heat loss exceeded metabolic heat production; (2) 50-55% from the systemic effects of the cold fluid per se; and (3) approximately 30% because the reduction in core heat content r emained partially constrained to core tissues. The postinfusion period was associated with a rapid and spontaneous recovery of core temperature. This increase in core temperature was nor associated with a peripheral-to-core r edistribution of body heat because core temperature remained warmer than pe ripheral tissues even at the end of the infusion. Instead, it resulted from constraint of metabolic heat to the core thermal compartment. Conclusions: Central venous infusion of cold fluid decreases core temperatu re more than would be expected were the reduction in body heat content prop ortionately distributed. It thus appears to be an effective method of rapid ly inducing therapeutic hypothermia. When the infusion is complete, there i s a spontaneous partial recovery in core temperature that facilitates rewar ming to normothermia.