THE ACUTE PHYSIOLOGY AND CHRONIC HEALTH EVALUATION-II CLASSIFICATION-SYSTEM IS A VALID MARKER FOR PHYSIOLOGICAL STRESS IN THE CRITICALLY ILL PATIENT

Objective: To compare the Acute Physiology and Chronic Health Evaluation (APACHE II) score with resting energy expenditure obtained from indirect calorimetry to determine whether the APACHE II scoring system is an accurate, objective measure of the degree of critical illness and physiologic stress between groups of patients. Design: Prospective study. Setting. University hospital, tertiary referral center. Patients: Seventy critically ill patients, consecutively sampled from burn, surgical, and medical intensive care units. Interventions: Indirect calorimetric studies were performed on each patient using a metabolic cart. The acute physiologic score component of the APACHE II scoring system was determined at the time of metabolic testing, a mean of 15.9 days after hospital admission. Measurements and Main Results: True resting energy expenditure was calculated by adjusting the measured energy expenditure for diet-induced thermogenesis and fever. A predicted resting energy expenditure was calculated for each patient using the Harris-Benedict equation alone, and by using the Harris-Benedict value corrected for previously published metabolic activity factors. To eliminate differences in body composition and size, true resting energy expenditure was divided by weight, body surface area, and Harris-Benedict resting energy expenditure. Results showed no significant correlation between APACHE II scores and either the Harris-Benedict resting energy expenditure or the Harris-Benedict value corrected by metabolic activity factors. However, there was a significant (p less-than-or-equal-to .001; r2 =.18 to.20) relationship between increasing APACHE II scores and both increasing measured and true resting energy expenditure. The true resting energy expenditure divided by body surface area, kilogram body weight, and Harris-Benedict predicted value, were all shown to be significantly (p < .01) related to APACHE II score, but showed no better degree of correlation (r2=.12 to.23) than comparison of APACHE II score with measured or true resting energy expenditure. Conclusions: The APACHE II classification may be a valid marker of physiologic stress as demonstrated by its statistically significant (although weak) relationship with indirect calorimetric measures of energy expenditure associated with varying degrees of critical illness.