The use of indirect calorimetry in critically ill patients--the relationship of measured energy expenditure to Injury Severity Score, Septic Severity Score, and APACHE II Score.

Abstract

The nutritional needs of critically ill septic patients or patients with multiple injuries are often difficult to estimate. Indirect calorimetry can simply and accurately determine individual caloric and nutritional needs, especially in cases of critically ill patients with complicated injuries. This prospective study compared the measured energy expenditures of 30 patients using indirect calorimetry with their predicted basal energy expenditure according to the Harris-Benedict equation, or their calculated energy expenditure derived from basal energy expenditure times, an activity factor, and a stress factor. These numbers were then used to evaluate the relationship between measured energy expenditure, measured energy expenditure per kilogram, and four specific scoring systems--the Septic Severity Score (SSS), the Injury Severity Score (ISS), the Trauma Score (TS), and APACHE II. The results showed the severity of sepsis or trauma correlated with the measured energy expenditure per kilogram of body weight. Among the 15 septic patients, in whom the measured energy expenditure per kilogram was 42.2 +/- 2.6 kcal/kg, the SSS provided a better predictor of energy needs and closer correlation with measured energy expenditure per kilogram (r = 0.69, Y = 1.41 + 0.72 X). Their stress factors could be modified as "0.97 + 0.0125 x SSS" to get a more accurate Harris-Benedict calculation. For the 15 patients with multiple injuries in whom the measured energy expenditure per kilogram was 34.9 +/- 1.6 kcal/kg, the ISS offered the best correlation with measured energy expenditure per kilogram (r = 0.84, Y = -31.47 +/- 1.73 X). Their stress factors could be modified as "1.04 + 0.0077 x ISS" to get a more accurate Harris-Benedict calculation.