Outcome prediction in critically ill patients by means of oxygen consumption index and simplified acute physiology score

Abstract

Both oxygen consumption index ($\dot V_{O_2 }$) and simplified acute physiology score (SAPS) are reported to be reliable predictors of the ultimate out-come in critically ill patients. The purpose of this study was to verify whether survivors and nonsurvivors have different $\dot V_{O_2 }$ and whether the prognostic potency of SAPS can be improved by addition of $\dot V_{O_2 }$ as a supplemental physiological variable. In 50 mechanically ventilated surgical ICU patients with heterogenous underlying diseases, SAPS was calculated and $\dot V_{O_2 }$ was determined by continuous 24-h measurement of oxygen consumption. The $\dot V_{O_2 }$ of survivors and nonsurvivors were not significantly different (p>0.05), which is in contrast to the results of earlier studies. This contrast may be explained by a difference both in methods of $\dot V_{O_2 }$ and in study populations. SAPS was significantly lower in survivors than in nonsurvivors (p(0.005) and was able to classify the patients correctly into groups of increasing probability of death. However, SAPS failed to be a helpful prognosticator in the individual patient. The addition of $\dot V_{O_2 }$ to SAPS as a supplemental physiological variable did not substantially improve the prognostic potency. Because a higher $\dot V_{O_2 }$ did not necessarily indicate a better survival chance, there is no argument for therapeutic interventions aimed exclusively at increasing $\dot V_{O_2 }$, as suggested previously.