Evaluation of stress factors and body weight adjustments currently used to estimate energy expenditure in hospitalized patients

Abstract

BACKGROUND: The purpose of this study was to critically examine current approaches for estimating energy expenditure and requirements of hospitalized patients requiring nutrition support. METHODS: All indirect calorimetry tests performed by our adult nutrition support service from 1991 to 2000 were reviewed. Stress factors were calculated as the measured energy expenditure divided by the predicted energy expenditure using the Harris-Benedict equation. Various methods for adjusting the body weights of obese subjects for use in the Harris-Benedict equation were evaluated. RESULTS: The average stress factor for these hospitalized patients was 1.25, and there were no differences in the stress factors between men and women. For obese subjects, using an adjusted body weight equal to ideal body weight plus 50% of the difference between ideal and actual body weight in the Harris-Benedict equation gave stress factors comparable with normal weight subjects. For underweight subjects, using the actual rather than ideal body weight gave stress factors that were most similar to normal weight patients. Disease-specific stress factors were calculated and compared with literature values. Mechanical ventilation, recent feeding, fever, and restlessness during the indirect calorimetry measurement increased the measured energy expenditure. CONCLUSIONS: Our findings provide nutrition support services with updated information on disease-specific stress factors that can be used for estimating energy expenditure in hospitalized patients. An adjusted body weight equal to ideal body weight plus 50% of the excess body weight should be used for estimating the energy requirements of obese patients requiring nutrition support.

A total of 576 indirect calorimetry tests performed by the adult nutrition support service were used to examine the accuracy of current approaches for estimating energy expenditure in hospitalized patients. Various methods for adjusting body weight of obese subjects were evaluated, and disease-specific stress factors were calculated. The effects of fever, agitation, mechanical ventilation, and recent feeding on indirect calorimetry measurements were determined.