The method of calculating the Acute Physiology and Chronic Health Evaluation (APACHE II) score was modified so that the score represented a point in time -- that is, it was calculated from the baseline data rather than from the worst values obtained during the first 24 hours of care in the intensive care unit. Data obtained at entry and every four hours thereafter for the first 44 hours and then at 72, 96, and 120 hours included the patient's temperature, mean systemic blood pressure, respiratory rate, heart rate, urinary output (as an hourly average), arterial-blood gas measurements and requirements for antipyretic agents. Values for mean blood pressure were calculated with the following formula: (0.33 x systolic pressure) + (0.67 x diastolic pressure. When a pulmonary artery catheter was present, the cardiac output, pulmonary artery pressure, pulmonary wedge pressure, and central venous pressure were measured at baseline and 20 hours later. Blood lactate was measured, and the delivery and consumption of oxygen calculated, at baseline and 20 hours. Blood samples were obtained at baseline and 20, 44, 72, and 120 hours after study entry for the measurement of hemoglobin, the total leukocyte count, the platelet count, bilirubin, serum aspartate aminotransferase, lactate dehydrogenase, creatinine, blood urea nitrogen, and electrolytes. Data were recorded on the patient's requirements for blood transfusion, intensive care, and mechanical ventilation.