Energy Expenditure in Critically Ill Obese Patients-A Prospective Observational Study

Introduction: In critically ill obese patients, both overfeeding and underfeeding have been associated with worsened outcomes, especially in mechanically ventilated patients. While indirect calorimetry (IC) is recommended to measure energy expenditure (EE), it is not widely available, and predictive formulas often lack accuracy. This study aimed to assess EE in critically ill obese patients and compare it with septic, non-obese patients as controls using IC. Methods: This prospective observational study was conducted at the University Medical Center Hamburg-Eppendorf, Germany, with 116 intensive care beds. EE was measured using IC at three timepoints: day 2-3 (acute phase), day 5-7 (end of acute phase), and day 10-15 (post-acute phase). Different reference weights were used to calculate EE, including ideal body weight (IBW), adjusted body weight (ABW), and total body weight (TBW). Nitrogen balance was also assessed to evaluate protein requirements. Results: We included 50 patients (28 obese and 22 controls). Equivalence between groups was found when ABW was calculated using 18% of excess body weight (EBW) at a mean of 24.4 kcal/kg/d for both groups. EE at the respective timepoints was 24.0 (95% confidence intervals: 22.1; 25.9), 24.2 (22.0; 26.5), 25.1 (21.4; 28.8) in obese and 24.9 (22.7; 27.0), 23.2 (20.7; 25.6), and 25.3 (21.8; 28.7) kcal/kg/d in control patients. Both groups exhibited a negative nitrogen balance, with the control group achieving nitrogen equilibrium by the post-acute phase. Conclusions: This study supports the ESPEN recommendation to base nutrition on ABW with 20% of EBW in obese critically ill patients when IC is unavailable. Further research is needed to determine optimal protein supplementation strategies and their timing to improve outcomes in this patient population.