Energy expenditure and withdrawal of sedation in severe head-injured patients.

Abstract

To determine the outcome of oxygen consumption (VO2) and energy expenditure after cessation of sedation in severe head-injured patients and to assess its usefulness as a predictor of neurologic severity. Prospective, descriptive study. Neurosurgical intensive care unit (ICU) in a university hospital. Fifteen severe head-injured patients with tracheostomies and who were mechanically ventilated and sedated at the time of the study. None. VO2 and energy expenditure were measured, using indirect calorimetry during and after discontinuation of sedation. After the measurement period, the patients were divided into two groups. Group 1 included patients who were completely weaned from sedation; group 2 included patients who had to be sedated again using predetermined criteria. In both groups, energy expenditure was close to basal energy expenditure during sedation, and increased to 150% of basal energy expenditure during the recovery period, with maximum hourly values 80% above basal energy expenditure. In group 1, VO2 and energy expenditure changed from 284 +/- 44 mL/min and 1833 +/- 261 kcal/day during sedation to 390 +/- 85 mL/min and 2512 +/- 486 kcal/day for the period without sedation. During this period, there was a significant correlation between VO2 and mean arterial pressure. For the recovery period, there was no difference in mean or maximum VO2 between the two groups of patients. At 24 and 48 hrs after cessation of sedation, VO2 and energy expenditure decrease to 30% above basal energy expenditure. These changes may be due to the recovery of muscular activity, weaning from mechanical ventilation, or an increase in the amount of circulating catecholamines. In severe head-injured patients, during the first 12 hrs after the discontinuation of sedation, the patients experienced a large increase in VO2, energy expenditure, and mean arterial pressure. Although these changes have no prognostic value in our study, they have potential deleterious effects in head-injured patients. Methods that blunt these changes which have proven efficacious in anesthesia may be effective for intensive care patients.