Circulatory indirect calorimetry in the critically ill.

Circulatory indirect calorimetry (CIC) is a potentially useful method to assess the energy requirements of critically ill patients. Unlike respiratory indirect calorimetry (RIC), which measures oxygen utilization from inhaled and exhaled gases, CIC measures oxygen utilization from arterial and mixed venous blood. Twenty-two measurements in eight critically ill patients comparing RIC, CIC, and commonly used estimates of energy expenditure were performed. A significant correlation between RIC and CIC was identified (r = 0.831, p less than 0.001). Poor correlation was noted with either method and the commonly used estimates. CIC may be a useful tool in estimating energy expenditures in the critically ill.