Objective, quantitative measurement of severity of illness in critically ill patients.

Severity of illness must be quantitated in critically ill patients if studies of outcome and therapeutic efficacy are to be meaningful. Objective physiologic indicators of critical illness, such as pertinent laboratory values, can be quantitated using the Therapeutic Intervention Scoring System--TISS. TISS data were obtained for 199 consecutive Class IV critically ill surgical ICU patients and compared to the same data obtained in less critically ill Class II and III ICU patients who served as the control group. For the physiologic indicators of critical illness, a wide range of normal values was established prospectively. The actual values generated by Class IV patients were compared to values of the same indicators as measured in Class II and III ICU patients. Of all objective indicators of critical illness, 55% were either outside the normal range or more than 2 SD away from the mean value of objective indicators for Class II and III ICU patients; 49% were beyond the normal range or more than 3 SD away. Of all TISS indicators, 73% were abnormal, and 36% of all physiologic indicators were still abnormal despite massive therapeutic support when compared to Class II or III ICU patients. Those patients who had more than 40% of their physiologic indicators abnormal were more likely to die. However, the percentage of abnormal TISS indicators did not discriminate between patients who died and those who lived, because almost all patients received massive support.(ABSTRACT TRUNCATED AT 250 WORDS)