CARBON-DIOXIDE REBREATHING METHOD OF CARDIAC-OUTPUT MEASUREMENT DURING ACUTE RESPIRATORY-FAILURE IN PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

Objective: To compare measurement of cardiac output by the CO2 rebreat hing method vs. the thermodilution cardiac output technique in the set ting of acute respiratory failure in patients with chronic obstructive pulmonary disease. Design: Prospective, comparative study of two meth ods in a consecutive sample.Setting: Intensive care unit. Patients: Tw enty-five patients with chronic obstructive pulmonary disease with acu te respiratory failure were studied. The patients were being mechanica lly ventilated and monitored with systemic and pulmonary artery cathet ers. Measurements and Main Results: Cardiac output was determined, usi ng both the thermodilution technique and an indirect CO2 Fick method. Veno-arterial CO2 content difference was calculated from an estimated mixed venous PcO(2), obtained by an equilibrium CO2 rebreathing method and measured PaCO2, PCO2, was converted to content using the equation of the CO2 dissociation curve described by McHardy. A wide range of c ardiac output was studied. There was a significant correlation between thermodilution and CO2 rebreathing methods (r(2) = .92, p < .001). Th e mean difference between thermodilution and CO2 rebreathing methods w as -0.06 L/min/m(2), standard deviation for the bias was 0.028 L/min/m (2), and 95% confidence interval for the bias was -0.120 to -0.001 L/m in/m(2). Conclusion: Our results suggest that the CO2 rebreathing meth od may be a reliable noninvasive technique to determine cardiac output in mechanically ventilated patients with chronic obstructive pulmonar y disease.