Lack of effect of sleep on energy expenditure and physiologic measures in critically ill burn patients.
Energy expenditure measurements, performed while patients are in standardized resting conditions, are often used as an indicator of care by which to evaluate the adequacy of nutrition support regimens. Little attention has been directed toward examining potential errors incurred by deriving daily energy needs based on a single 15- to 20-minute measurement. This study was designed to differentiate energy expenditure during periods of sleep (defined as time spent in any of the standard sleep stages) and wakefulness in pediatric burn patients. Twenty-four-hour indirect calorimetry, polysomnography, and physiologic assessments (mean arterial pressure, heart rate, body temperature, oxygen saturation, and respiratory rate) were conducted simultaneously in 14 patients, who were thermally injured and tracheally intubated, for a total of 45 24-hour intervals. Mean age of the patients was 10.8+/-1.2 years. Mean total body surface area of the injury was 55.7+/-4.7%, and mean full-thickness burn was 48.8+/-6.0%. A nested general linear analysis of variance model was used to evaluate the association between sleep, wakefulness, and energy needs; adjustments were made for postburn day and multiple test runs per patient. On average, subjects slept 699+/-46 minutes/day. They experienced a large number of awakenings from sleep (mean=53+/-6.3 awakenings per 24 hours). Patients had mean energy expenditure of 2,529+/-396 kcal/day while awake and 2,360+/-291 kcal/day while asleep, and these mean values did not differ significantly. No differences in physiologic measurements during the awake and sleep states were found. There appears to be little difference in the metabolism of seriously injured burn patients while asleep and while awake. The study deemphasizes the importance of performing indirect calorimetry at rest in critically ill pediatric burn patients, and it supports the extrapolation of daily energy expenditure from a 15- to 20-minute steady-state measurement obtained during either sleep or wakefulness.