The metabolic effect of induced mild hypothermia in critically ill patients

Introduction

The aim of our study was to evaluate the metabolic effect of induced mild hypothermia in critically ill patients and to assess if rewarming reverses these effects.

Methods

During a 2 year period, 12 consecutive critically ill patients under continuous veno-venous hemofiltration (CVVH), due to acute renal failure, were studied prospectively. All patients were mechanically ventilated, nine of them were sedated but none was paralyzed. Core temperature (T) was continuously monitored through a nasopharyngeal sensor, while resting energy expenditure (REE), V_O2 and V_CO2 were evaluated by means of indirect calorimetry. Baseline measurements were recorded before the onset of CVVH. Serial measurements were performed each time T was decreased by 1°C. After the interruption of CVVH, measurements were also repeated serially with the increase of core temperature of 1°C.

Results

Decrease of temperature from 37°C to 35°C has no statistically significant influence on metabolic demands. During the reduction of temperature from 38°C to 35°C a statistically significant decrease in REE (2593 ± 228 kcal vs 2095 ± 618 kcal, P = 0.041), as well as in V_CO2 (P = 0.051) was observed. A difference at the limits of significance was also observed in REE from 38°C to 36°C (2593 ± 228 kcal vs 2292 ± 434 kcal, P = 0.056). Rewarming was followed by a gradual reverse of these effects.

Statistics were calculated with SPSS version 10, using nonparametric tests. Correlation between T, REE, V_O2 and V_CO2 was tested by Pearson's correlation coefficient. Comparison between REE, V_O2 and V_CO2 at different temperatures was performed using Student's paired t test.

Conclusion

Mild hypothermia does not affect the metabolic rate in critically ill patients. Cooling in the febrile critically ill patient is followed by a significant decrease in energy expenditure. This may prove beneficial, minimizing the potential for tissue hypoxia, in situations of limited oxygen delivery.