Discrepancies in Cardiac Output Measurements in Low LVEF Cardiac Surgery Patients

Overview

This pilot study evaluated the feasibility and accuracy of the pressure recording analytical method (PRAM) for cardiac output measurement in high-risk cardiac surgery patients with severely reduced left ventricular ejection fraction (LVEF < 35%). While PRAM demonstrated high feasibility for data acquisition, it significantly underestimated cardiac output compared to pulmonary artery catheter (PAC) thermodilution and showed poor trending ability.

Background

Continuous hemodynamic monitoring is critical for managing patients undergoing coronary artery bypass graft surgery, especially those at risk for low-output syndrome due to impaired left ventricular function. The pulmonary artery catheter (PAC) remains the gold standard for cardiac output measurement but is invasive and carries risks. Pulse contour analysis methods, such as PRAM, offer less invasive alternatives by analyzing arterial pressure waveforms to estimate cardiac output without external calibration. However, their accuracy in patients with severe cardiac dysfunction remains uncertain.

Data Highlights

Key Findings

• PRAM achieved high feasibility with 98.8% successful data acquisition in patients with LVEF < 35% undergoing CABG surgery.
• PRAM significantly underestimated cardiac output by an average of 2.02 L/min compared to PAC thermodilution.
• The percentage error of PRAM measurements was 134.3%, far exceeding the acceptable 30% threshold for clinical interchangeability.
• Trending ability of PRAM was poor, with four-quadrant and polar concordance rates of 36.6% and 10.1%, respectively.
• The complex pathophysiology and severely reduced ejection fraction likely impair PRAM accuracy in this high-risk population.

Clinical Implications

Although PRAM is feasible for continuous cardiac output monitoring via a peripheral arterial site, its significant underestimation and poor trending in patients with severely reduced LVEF limit its reliability for guiding hemodynamic management in this population. Clinicians should exercise caution when interpreting PRAM-derived cardiac output values in such high-risk cardiac surgery patients and consider confirmation with established methods like PAC thermodilution.

Conclusion

PRAM, despite its theoretical advantages and feasibility, demonstrated poor agreement and unreliable trending compared to PAC in cardiac surgery patients with severely impaired left ventricular function. Further research is needed to optimize or adapt PRAM algorithms for accurate use in this challenging clinical setting.

Related Resources & Content

1. COMPARE Statement 2021 -- Guidelines for Cardiac Output Method Comparison