Errors in estimating energy expenditure in critically ill surgical patients

Thirty-one critically ill surgical patients were receiving central parenteral nutrition. All were intubated, and 29 were receiving mechanical ventilatory support. Nutritional and metabolic data were recorded at the time of indirect calorimetry. Measured energy expenditure (MEE) was compared with predictions of basal energy expenditure (BEE) and calculated energy expenditure, defined as the product of BEE and a stress factor estimated by the nutrition support service to account for severity of illness and activity. The MEE was significantly greater than the BEE and significantly less than the calculated energy expenditure. The estimated stress factor was significantly greater than the actual MEE/BEE ratio, and the correlation between these values was poor. Clinical assessment may overestimate energy expenditure in critically ill patients because of the apparent degree of illness used to determine the stress factor. Bedside indirect calorimetry may be useful to assess more accurately energy expenditure and optimize nutritional support.