Influence of body temperature, with or without sedation, on energy expenditure in severe head-injured patients

Objective: To quantify the effect of body temperature and sepsis on energy expenditure in head injured patients. Design: Prospective, nonrandomized, observational study, Setting: Neurosurgical intensive care unit, Patients: Severe head-injured patients, Interventions: Use of an indirect calorimeter to measure energy expenditure. Measurements and Main Results: Mean arterial pressure (MAP), heart rate (HR), body temperature, and mean hourly energy expenditure were recorded. Twenty four patients had 1,919 hourly measures of the above parameters, The measurement periods were divided into four groups, according to the anesthetic agents used for sedation: fentanyl and midazolam (group FM); fentanyl, midazolam, and curarization (group C); thiopental (group T); and no sedation (group NS), The energy expenditure/basal energy expenditure ratio (EE/BEE) was significantly lower in group T (1.20 +/- 0.15) than in group FM (1.32 +/- 0.24) or group C (1.32 +/- 0.20) and was significantly higher in group NS (1.60 +/- 0.33). There was a significant correlation between body temperature and EE/BEE (p < .0001, r(2) = .27) only in sedated patients, Using the equation of the regression line to correct energy expenditure for differences in body temperatures betweens groups, the difference in energy expenditure between groups with sedation disappeared, This finding suggested that the low energy expenditure under thiopental was due only to hypothermia. Sepsis significantly increased energy expenditure independently of fever, There was a weak but statistically significant correlation between energy expenditure and HR (p < .01, r(2) = .13) but not between energy expenditure and MAP. Conclusions: Sedation had a major effect on energy expenditure. In sedated patients, body temperature was the main determinant of energy expenditure; the anesthetic agent used had little influence on the level of energy expenditure. Sepsis increased energy expenditure independently of fever, probably through hormonal changes.