EFFECT OF COOLING ON OXYGEN-CONSUMPTION IN FEBRILE CRITICALLY ILL PATIENTS

Hyperthermic critically ill patients are commonly cooled to reduce the ir oxygen consumption (Vo(2)). However, no previous studies in febrile humans have measured Vo(2) during cooling. We cooled 12 febrile, crit ically ill, mechanically ventilated patients while measuring VO2 and C O2 production (VCO2) by analysis of inspired and expired gases. All pa tients were mechanically ventilated for hypoxemic, hypercapneic, or sh ock-related respiratory failure and had a mean APACHE II score of 22.4 +/- 7.7. As temperature was reduced from 39.4 +/- 0.8 to 37.0 +/- 0.5 degrees C, VO2 decreased from 359.0 65.0 to 295.1 +/- 57.3 ml/min (p < 0.01) and VCO2 decreased from 303.6 +/- 43.6 to 243.5 +/- 37.3 ml/mi n (p < 0.01). The respiratory quotient (RQ) did not change significant ly, and calculated energy expenditure decreased from 2,481 +/- 426 to 1,990 +/- 33 kcal/day (p < 0.01). In 7 patients with right heart cathe ters, cardiac output decreased from 8.4 +/- 3.2 to 6.5 +/- 1.8 L/min ( p < 0.01) as the oxygen extraction fraction also tended to decrease fr om a mean of 28.2 +/- 6.8 to 23.4 +/- 4.7% (p = 0.12) during cooling. Accordingly, cooling the febrile patient unloads the cardiorespiratory system and, in situations of limited oxygen delivery or hypoxemic res piratory failure, may thus facilitate resuscitation and minimize the p otential for hypoxic tissue injury.