[Evaluation of energy metabolism in burn patients: indirect calorimetry predictive equations]

Knowing the most reliable method for measuring the metabolic energy use (MEU), is of great importance in patients with severe burns. For the calculation of the energetic requirements of large burn patients, several predictive equations (PE's) are used, based on weight, size, age, body surface area (BSA), and burned body surface (BBS). Previous studies note the tendency for over-or underestimating the MEU, depending on whether one or another PE is used, which is why it is considered necessary to calculate the energy requirements in the most exact manner possible, which can be done by means of indirect calorimetry (IC).

18 patients (14 men and 4 women) who were admitted to the Burn Unit between 1994 and 1995, were included in the study, with the following inclusion criteria; age > 18 years and < 65 years, and who presented deep burns on are than 15% of the body surface. The MEU of the patients was evaluated by means of IC, using a Deltatrac il unit. The MEU calculated by means of IC was compared with that calculated by means of the four most commonly used PE's in literature: Long Formula: MEU = Basal energy use (BEU) x activity factor x aggression factor which is variable according to the BBS; Curreri Formula: MEU = (Weight x 25) + (total BBS x 40); MEU = 2000 x BSA. As statistical methods, one looked for the existence of correlation, by means of the Pearson method, and the "r" were compared by means of the Fischer conversion. The regression coefficient was found among the values obtained through the PE's and those measured by IC, as well as among those of IC and the percentage of deep burn and the total burned body surface.

All the formulate included overestimated the MEU measured between 30.6% and 43.8% with the 2 x MEU formula being the one which did so least (30.6%). In any of them, there is an important variation of the percentage of overestimation with respect to the average MEU in this group. All are correlated in an important way with the MEU. The reliability of these PE's is variable, as is shown by the slopes of the regression lines, with the most reliable PE being that of 2000 x BSA, and that of 2 x MEU, by Harris-Benedict. There is also correlation between the average MEU by IC and the deeply burned body surface.

This study proves the usefulness of the IC for knowing the EME in burn patients, to prevent their hypernutrition, as well as the relative value of the formulae usually used clinically to estimate this parameter.