Comparison of simultaneous estimation of cardiac output by four techniques in patients undergoing off-pump coronary artery bypass surgery--a prospective observational study.

We prospectively compared four techniques of cardiac output measurement: bolus thermodilution cardiac output (TDCO), continuous cardiac output (CCO), pulse contour cardiac output (PiCCO), and Flowtrac (FCCO), simultaneously in fifteen patients undergoing off-pump coronary artery bypass grafting (OPCAB). All the patients received pulmonary artery catheter (capable of measuring both bolus thermodilution cardiac output and CCO), PiCCO arterial cannula in the left and FCCO in the right femoral artery. Cardiac indices (CI) were obtained every fifteen minutes by using all the four techniques. TDCO was treated as 'control' and the rest were treated as 'test' values. Interchangeability of techniques with TDCO was assessed by Bland and Altman plotting and mountain plot. Four hundred and thirty eight sets of data were obtained from fifteen patients. The values of cardiac output varied between 1 to 6.9 L/min. We found that the values of all the techniques were interchangeable. At certain times, the values of CI measured by both PiCCO and FCCO appeared erratic. The values of CI measured simultaneously appeared in the following descending order of accuracy; TDCO>CCO>FCCO>PiCCO (the % times TDCO correlated with CCO, FCCO, PiCCO was 93, 86 and 80 respectively). The bias and precision (in L/min) for CCO were 0.03, 0.06, PiCCO 0.13, 0.1 and flowtrac 0.15, 0.04 respectively suggesting interchangeability. We conclude that the cardiac output measured by CCO technique and the pulse contour as measured by PiCCO and FCCO were interchangeable with TDCO more than 80% of the times.