Heart Rate and Metabolic Response to Burn Injury in Humans

Background: Although frequently done, estimating the energy requirements of individual burn patients without measuring their resting metabolic rate is a less than satisfactory method of evaluation. Methods: We tested whether heart rate, which relates to the energy expenditure during physical activity, is also associated with postburn hypermetabolism (calculated as percentage increase of resting metabolic rate above the predicted normal fasting resting metabolic rate). Twenty-three patients [12 men and 11 women, aged 38 ± 13 years (mean ± SD); weight, 71.6 ± 14.8 kg; body mass index, 25.4 ± 3.6; total burn surface area, 35.3 ± 17.8% (percentage of body surface)] were studied weekly for 3 weeks after an overnight fast. Results: Measured resting metabolic rates and heart rates were 2016 ± 497 kcal/d, 101 ± 13 bpm (n = 19); 2231 ± 485 kcal/d, 107 ± 13 bpm (n = 18); and 1903 ± 598 kcal/d, 99 ± 14 bpm (n = 11) for weeks 1, 2, and 3, respectively. Postburn hypermetabolism was +36% ± 19%, +55% ± 27%, and +36% ± 35% in the first, second, and third week, respectively. In each week postburn hypermetabolism correlated with heart rate (r = 0.65, p = .003; r = 0.69, p = .001; and r = 0.80, p = .002, respectively). Only in the second week did postburn hypermetabolism correlate with total burn surface area (r = 0.52, p = .02); there was no correlation with body temperature. In a multiple regression analysis, predicted resting metabolic rate, heart rate, and total burn surface area together explained 77% of all of the variance observed in the 48 fasting resting metabolic rates that were measured in the study (r² = 0.77, p < .0001), and each of these variables also had a significant partial correlation with fasting resting metabolic rates (r² = 0.45, p < .0001; r² = 0.29, p < .0001; and r² = 0.03, p < .03, respectively). Conclusions: In burn patients, variability in heart rate is associated with a significant part of postburn hypermetabolism variability. Therefore, heart rate may be considered a useful variable to be used for the evaluation of the energy requirements of severely burned patients. (Journal of Parenteral and Enteral Nutrition 19:55-62, 1995)