Determination of the energy requirements in mechanically ventilated critically ill elderly patients in different BMI groups using the Harris–Benedict equation

Abstract

Background: Due to studies on calorie requirement in mechanically ventilated critically ill elderly patients are few, and indirect calorimetry (IC) is not available in every intensive care unit (ICU). The aim of this study was to compare IC and Harris–Benedict (HB) predictive equation in different BMI groups. Methods: A total of 177 mechanically ventilated critically ill elderly patients (≧65 years old) underwent IC for measured resting energy expenditure (MREE). Estimated calorie requirement was calculated by the HB equation, using actual body weight (ABW) and ideal body weight (IBW) separately. Patients were divided into four BMI groups. One-way ANOVA and Pearson's correlation coefficient were used for statistical analyses. Results: The mean MREE was 1443.6 ± 318.2 kcal/day, HB(ABW) was 1110.9 ± 177.0 kcal/day and HB(IBW) was 1101.5 ± 113.1 kcal/day. The stress factor (SFA = MREE ÷ HB(ABW)) was 1.43 ± 0.26 for the underweight, 1.30 ± 0.27 for the normal weight, 1.20 ± 0.19 for the overweight, and 1.20 ± 0.31 for the obese. The SFI (SFI = MREE ÷ HB(IBW)) was 1.24 ± 0.24 for the underweight, 1.31 ± 0.26 for the normal weight, 1.36 ± 0.21 for the overweight, and 1.52 ± 0.39 for the obese. MREE had significant correlation both with REE(ABW) = HB(ABW) × SFA (r = 0.46; P < 0.0001) and REE(IBW) = HB(IBW) × SFI (r = 0.43; P < 0.0001). Conclusion: IC is the best accurate method for assessing calorie requirement of mechanically ventilated critically ill elderly patients. When IC is not available, using the predictive HB equation is an alternative choice. Calorie requirement can be predicted by HB(ABW) × 1.20–1.43 for critically ill elderly patients according to different BMI groups, or using HB(IBW) × 1.24–1.52 for patients with edema, ascites or no available body weight data. Keywords: Body Mass Index, Elderly critical care, Harris–Benedict equation, Indirect calorimetry