Resting energy expenditure in non-ventilated, non-sedated patients recovering from serious traumatic brain injury: comparison of prediction equations with indirect calorimetry values

Background & aims
Little is known about energy requirements in brain injured (TBI) patients, despite evidence suggesting adequate nutritional support can improve clinical outcomes. The study aim was to compare predicted energy requirements with measured resting energy expenditure (REE) values, in patients recovering from TBI.

Methods
Indirect calorimetry (IC) was used to measure REE in 45 patients with TBI. Predicted energy requirements were determined using FAO/WHO/UNU and Harris–Benedict (HB) equations. Bland–Altman and regression analysis were used for analysis.

Results
One-hundred and sixty-seven successful measurements were recorded in patients with TBI. At an individual level, both equations predicted REE poorly. The mean of the differences of standardised areas of measured REE and FAO/WHO/UNU was near zero (−9 kcal) but the variation in both directions was substantial (range −591 to +573 kcal). Similarly, the differences of areas of measured REE and HB demonstrated a mean of 1.9 kcal and range −568 to +571 kcal. Glasgow coma score, patient status, weight and body temperature were significant predictors of measured REE (p < 0.001; R2 = 0.47).

Conclusions
Clinical equations are poor predictors of measured REE in patients with TBI. The variability in REE is substantial. Clinicians should be aware of the limitations of prediction equations when estimating energy requirements in TBI patients.