Cardiac output monitoring by pressure recording analytical method in cardiac surgery.

OBJECTIVE: A less-invasive method has been developed that may provide an alternative to monitor cardiac output from arterial pressure: beat-to-beat values of cardiac output can be obtained by pressure recording analytical method (PRAM). The purpose of this study was to assess the reliability of cardiac output determination by PRAM in cardiac surgery.

METHODS: Cardiac output was measured in 28 patients undergoing coronary artery bypass grafting at 15 min after anaesthesia induction, 30 min after extracorporeal circulation, 1 and 3 h after arrival in the intensive care unit using thermodilution (ThD) method through a pulmonary artery catheter and PRAM. ThD cardiac output was calculated as the mean of five separate measurements. PRAM provided beat-by-beat cardiac output data continuously throughout the study and the cardiac output values displayed on a dedicated personal computer at each time point were recorded. Correlations were calculated and differences were compared by Bland-Altman analysis.

RESULTS: A total of 112 measurements were obtained. Cardiac output ranged from 2.3 to 7.4 l/min, and a good linear correlation (R2=0.78, P<0.0001) was found between ThD and PRAM. The highest degree of correlation (R2=0.86) was obtained at 3 h after arrival in the intensive care unit. The lower degree of correlation (R2=0.70) was obtained 30 min after extracorporeal circulation. At Bland-Altman analysis, the overall estimates of cardiac output measured by PRAM closely agreed with ThD (mean difference, 0.027; standard deviation, 0.43; limits of agreement, -0.83 and +0.89).

CONCLUSIONS: Under the studied conditions, our results demonstrate good agreement between PRAM data and ThD measurements, and this new method has shown to be accurate for real-time monitoring of cardiac output in cardiac surgery. Further studies will be required to assess this method in higher-risk patients and in the setting of haemodynamic instability or arrhythmias. This is the first study designed to assess the accuracy of PRAM in cardiac surgery.