Beat-by-beat measurement of cardiac output during aortocoronary surgery

Introduction

Unavailability of online continuous data, invasiveness, and expensiveness are the major drawbacks of the most commonly employed techniques to measure cardiac output. Cardiac output (CO) is often monitored after cardiac operations with a pulmonary artery catheter. A new method has been introduced that measures cardiac output by arterial pressure (pressure recording analytical method [PRAM]) without calibration by thermodilution (ThD). This study assessed the reliability of cardiac output determinations by PRAM before, during and after cardiac surgery.

Materials and methods

In 12 patients undergoing aortocoronary bypass surgery, between September and November 2002 at the Department of Cardiothoracic Surgery of the University of Siena, CO was measured after induction of anesthesia, after closure of the sternum, and upon returning to the ICU (30 min and 3 hours) by thermodilution and PRAM. PRAM is a new method based on the objective mathematical analysis of changes of arterial pressure profile with time. PRAM allows real time beat-by-beat CO assessment from the pressure signals recorded in radial artery without calibration by ThD. Cardiac output (l/min) was measured continuously throughout the duration of the study.

Statistical analysis

CO values obtained at the same time of the ThD dilution curve (240 paired data) were used for the comparison by linear correlation and Bland–Altman analyses. ThD, the established clinical method to measure CO, was taken as the independent variable.

Results

The correlation between PRAM and ThD CO values was 0.83 (R² = 0.69; P < 0.01) with a bias of 0.05 (95% CI -0.71 to 0.81). The correlation at 3 hours from arrival at ICU (the moment of steady-state clinical condition) showed a better agreement (R² = 0.82; P < 0.001) with a bias of 0.02 (95% CI -0.78 to 0.86).

Conclusions

In this small series of cardiac surgery patients, PRAM reflects ThD values and permits one to monitor continuously CO with reduced invasiveness and at a much lower cost with respect to ThD. In conclusion, PRAM provides reliable estimates of cardiac output in hemodynamically stable and unstable cardiac patients.