Cardiac output measurement using a modified carbon dioxide Fick method: comparison analysis with pulmonary artery catheter method and pulse induced contour cardiac output method.

OBJECTIVES: In the present study, cardiac output in mechanically ventilated patients were determined using three methods including modified CO2-Fick (mCO2F), pulmonary artery catheter (PAC), and pulse induced contour cardiac output (PiCCO) methods and the results were compared to assess the effectiveness of mCO2F method in measuring the cardiac output. METHOD: Mechanically ventilated and hemodynamically unstable patients (n=39) were sedated and intubated with Swan-Ganz or PiCCO arterial catheters. At the beginning of the experiment and at 4 h after the experiment, the CO2 concentration in expiratory air was measured through a CO2 monitor and it was used further in the cardiac output calculation using mCO2F method. The cardiac output was also determined using PAC and PiCCO methods. RESULTS: The cardiac output determined by PAC and mCO2F method was not significantly (P>0.05) different [5.53±2.85 L.min(-1) (PAC) and 5.96±2.92 L.min(-1) (mCO2F)] at the beginning of the experiment and [6.22±2.7 L.min(-1) (PAC) and 6.36±2.35 L.min(-1) (mCO2F)] at 4 h after the experiment; however, they were highly correlated (r=0.939 and 0.908, P<0.001). The cardiac output determined by PiCCO and mCO2F method was also not significantly (P>0.05) different [6.05±2.49 L.min(-1) (PiCCO) and 5.44±1.64 L.min(-1) (mCO2F)] at the beginning of the experiment, and [6.17±2.04 L.min(-1) (PiCCO) and 5.70±1.72 L.min(-1) (mCO2F)] at 4 h after the experiment; however, they were highly correlated (r=0.776 and 0.832, P<0.001). CONCLUSION: The mCO2F method could accurately measure the cardiac output in mechanically ventilated patients without using any expensive equipment's and invasive procedures.