Energy expenditure and caloric balance after burn: increased feeding leads to fat rather than lean mass accretion

Abstract

Objective: Resting energy expenditure (REE) is commonly measured in critical illness to determine caloric "demands" and thus nutritive needs.

Summary background data: The purpose of this study was to 1) determine whether REE is associated with clinical outcomes and 2) determine whether an optimal caloric delivery rate based on REE exists to offset erosion of lean mass after burn.

Methods: From 1995 to 2001, REE was measured by indirect calorimetry in 250 survivors of 10 to 99%TBSA burns. Caloric intake and REE were correlated with muscle protein catabolism, length of stay, ventilator dependence, sepsis, and mortality. From 1998 to 2000, 42 patients (>60%TBSA burns) received continuous enteral nutrition at a spectrum of caloric balance between 1.0x REE kcal/d -1.8x REE kcal/d. Serial body composition was measured by dual energy x-ray absorptiometry. Lean mass, fat mass, morbidity, and mortality were determined.

Results: REE/predicted basal metabolic rate correlated directly with burn size, sepsis, ventilator dependence, and muscle protein catabolism (P <.05). Declining REE correlated with mortality (P <.05). 2) Erosion of lean body mass was not attenuated by increased caloric balance, however, fat mass increased with caloric supply (P <.05).

Conclusion: In surviving burned patients, caloric delivery beyond 1.2 x REE results in increased fat mass without changes in lean body mass. Declining energy expenditure appears to be a harbinger of mortality in severely burned patients.

Figures

Fig. 1. Linear correlation between fat mass and lean body mass with caloric delivery indexed to measured resting energy expenditure. Increasing caloric delivery relative to resting energy expenditure increased fat accretion without effects on lean body mass.

Fig. 2. Linear correlation between total body weight and caloric delivery indexed to measured resting energy expenditure. Increasing caloric delivery increased total body weight to the extent that no change in total body weight was seen at approximately 1.5 × REE. From the data on lean body mass, we conclude that the total body weight at higher caloric intakes was maintained by the addition of fat mass in the face of lean body mass loss.

Fig. 3. Plot of resting energy expenditures expressed as percentage of predicted basal metabolic rate from the Harris-Benedict equation. Points are from survivors, and lines are from nonsurvivors. Nonsurvivors were characterized by a drop in resting energy expenditure before death.