Background: Adequate nutritional replacement of critically ill and injured patients is of paramount importance, as it decreases infectious morbidity and mortality. However, multiple methods of determining nutritional requirements exist, including mathematical formulas, weight based calculations, and the use of metabolic cart measurements, the latter of which is associated with significant labor and equipment costs. We hypothesized that metabolic cart measurements, despite increasing the cost of care, would more accurately determine nutritional requirements in a critically ill population than formulaic or weight-based calculations.
Methods: Consecutive metabolic cart measurements were prospectively obtained on 59 critically ill surgery and trauma patients, and compared with predicted values as determined by the Harris-Benedict equation and weight-based calculations. Comparison was made to actual resting energy expenditure data acquired via indirect calorimetry data obtained from serial metabolic carts.
Results: There were 59 patients who formed the study population, with 37% of the population having two or more metabolic cart readings (total number of cart readings was 106). There was no statistically significant difference between the metabolic cart results, the predicted resting energy expenditure as calculated by the Harris-Benedict equation adjusted with a factor of 1.5, and a weight based calculation at 30 kcal/kg adjusted body weight. Metabolic requirements were stable over time (4-48 days) without significant variation. Nutritional parameters, as evaluated by the visceral proteins prealbumin and transferrin significantly increased with time in injured patients.
Conclusions: Either 30 kcal/kg adjusted body weight or the resting energy expenditure calculated from the Harris-Benedict equation multiplied by 1.5 adequately predicts the nutritional requirements of critically ill surgery and trauma patients. The addition of metabolic cart data does not provide any additional information in the determination of caloric needs in the critically ill and injured patient. In this population, omission of metabolic cart data would have saved 33,000 dollars without adversely affecting patient outcome.