A Comparison of Four Methods of Determining Caloric Requirements of Mechanically Ventilated Trauma Patients

Abstract

Because the nutrition of critically ill patients is an important part of their management, and because there are a number of ways to estimate such patients' caloric requirements, we compared the results of using four different methods of estimating caloric requirements. Methods: In 15 critically ill, mechanically ventilated trauma patients, we analyzed inspired and expired gases for PO₂, PCO₂ and we measured expired gas volumes. We then calculated $\stackrel{\cdot }{\text{V}}{\text{O}}_2$ , and caloric requirements, using (1) the Harris-Benedict equation, (2) the Weir equation, (3) the O₂ caloric equivalent, and (4) the CO₂ caloric equivalent. Results: A total of 46 comparisons were made in the 15 patients. The mean ± standard deviation caloric requirements (in kcal/day) were (1) 1716 ± 225 with the Harris-Benedict equation, (2) 2755 ± 696 with the Weir equation, (3) 2712 ± 971 with the O₂ caloric equivalent, and (4) 2677 ± 845 with the CO₂ caloric equivalent. There was a significant difference among the caloric requirements indicated by the four methods (P < 0.001 by analysis of variance); the Harris-Benedict equation method significantly underestimated the caloric requirements. However, there was no significant difference among the caloric requirements indicated by the Weir equation, the O₂ equivalent, and the CO₂ equivalent (P = 0.27 by analysis of variance). Conclusions: Because use of the Harris-Benedict equation in this study resulted in significant underestimation of the caloric requirements of mechanically ventilated, critically ill patients, we recommend use of one of the other three methods studied. In this patient population, it was equally satisfactory to use the Weir equation, the O₂ caloric equivalent, or the CO₂ caloric equivalent to calculate caloric requirements. (Respir Care 1986;31:1197-1203.)