Poor agreement between cardiac output measurements from the pressure recording analytical method and pulmonary artery thermodilution in patients with low cardiac output: preliminary results from a prospective observational method comparison pilot study

Background Continuous hemodynamic monitoring is essential for guiding goal-directed therapy in high-risk cardiac surgery patients, particularly those prone to low-output syndrome. The pressure recording analytical method (PRAM) is a unique, uncalibrated pulse contour analysis technology that estimates cardiac output (CO) by directly analyzing the arterial pressure waveform. Objectives The primary objective of this prospective observational pilot study was to investigate the feasibility of the PRAM method (test method) in a challenging, high-risk cardiac surgery population defined by a severely impaired left ventricular ejection fraction (LVEF 35%). The exploratory objective was to perform a preliminary analysis of the agreement between PRAM-derived and pulmonary artery catheter (PAC)-derived continuous cardiac output (FastCCO) measurements. Design This was a prospective, observational method comparison pilot study. Methods Seven patients (LVEF 35%) undergoing coronary artery bypass surgery were included. Concurrent measurements ( n = 826) were collected via radial artery (PRAM) and PAC. To account for repeated measures, agreement was assessed using linear mixed-effects (LME) modeling, and 95% confidence intervals (CI) were derived using 100,000 bootstrap statistics. Trending ability was assessed via four-quadrant and polar plot analysis. Results Feasibility was high (98.8% data acquisition). However, the LME constant bias model revealed a significant population-level underestimation by PRAM of −2.02 L/min (limits of agreement: −5.69 to 1.64 L/min). The bias-corrected and accelerated-bootstrapped percentage error was 134.3% (95% CI: 122.7–148.3%), and the least significant change was 4.48 L/min (95% CI: 4.31–4.74 L/min). Trending ability was severely compromised, with a four-quadrant concordance rate of 36.6% and a polar concordance rate of 10.1%. Conclusions While feasible in terms of data acquisition, the PRAM method, when applied via a peripheral arterial site, showed poor agreement and unreliable trending ability compared with PAC FastCCO in cardiac surgery patients with severely reduced left ventricular function. These findings suggest that the complex pathophysiology, particularly the associated severe low ejection fraction, may compromise the accuracy of PRAM in this high-risk population. Further investigation is warranted to understand the influence of these specific conditions on the PRAM algorithm. Clinical Trial Registration: https://drks.de/search/en/trial/DRKS00017260/details .