Measurements of cardiac output in seriously ill patients using a CO2 rebreathing method

A CO2 rebreathing method for the measurement of cardiac output was evaluated by comparison with the direct Fick O2 method in 26 studies performed in 18 patients who were critically ill. The method requires measurement of CO2 output by collection of expired gas, of arterial PCO2, and of mixed venous PCO2 by rebreathing. Twenty-five comparisons were within +/- 20% of the direct Fick measurements, at cardiac outputs varying between 1.4 and 6.4 L/min. Knowledge of the cardiac output increased the quality of the interpretation of arterial blood PO2 measurements in the assessment of pulmonary gas exchange disturbances.