Measurement of metabolism in multiple organ failure

Abstract

Despite the emphasis on surgical nutrition, clinical research and practice are usually based on gross estimation of caloric requirements and no specific knowledge of caloric balance. One reason for this is the difficulty of measuring O2 and CO2 exchange in critically ill patients. We designed a system for intensive care unit (ICU) bedside measurement of O2 consumption (VO2), CO2 production (VCO2), respiratory quotient (RQ), and indirect calorimetry (E). We measured these variables daily in 57 surgical ICU patients at risk for multiple organ failure. Measured VO2 and E varied widely (+/- 40%) from estimated values. Seventeen patients had a cumulative negative balance of at least 10,000 calories; 13 died. This caloric deficient was reversed by caloric intake in three of these patients; one died. Fifteen patients had positive caloric balance. Only four of these died, but the CO2 load produced by hypercaloric feeding created ventilator weaning problems in some patients. Ventilator weaning was facilitated by decreasing total calories and substituting fat for carbohydrate to reduce the RQ. The incidence of multiple organ failure was higher in patients with large caloric deficits, although cause and effect are not inferred. We conclude that respirometry and indirect calorimetry are helpful for management and essential for nutritional research.