Continuous Fick cardiac output compared to thermodilution cardiac output

Area of Science:

• Cardiovascular physiology
• Critical care medicine
• Biomedical engineering

Background:

• Accurate cardiac output monitoring is crucial for managing critically ill patients.
• Existing methods like thermodilution have limitations for continuous assessment.
• The oxygen Fick equation provides a physiological basis for cardiac output calculation.

Purpose of the Study:

• To develop and evaluate a novel continuous monitoring system for cardiac output based on the oxygen Fick equation.
• To compare the performance of this Continuous Fick (CF) method against traditional thermodilution (TD) cardiac output measurement.
• To assess the practicality and advantages of the CF method in post-cardiac surgery patients.

Main Methods:

• A computer-based system was developed integrating a gas exchange analyzer and oximetry.
• Continuous measurement of oxygen consumption and arteriovenous oxygen difference.
• Simultaneous cardiac output measurements using CF and TD methods in 21 ventilated post-cardiac surgery patients.

Main Results:

• A total of 237 simultaneous cardiac output measurements were obtained, ranging from 2 to 11 L/min.
• A strong correlation (r = .86) was observed between CF and TD cardiac output.
• The CF method consistently underestimated cardiac output compared to TD, with greater discrepancies at lower flow rates (TD = 0.92 * CF + 1.16).

Conclusions:

• Continuous Fick cardiac output monitoring is a practical method for critically ill patients.
• The CF method offers advantages in simultaneously evaluating cardiac output, oxygen demand, and oxygen extraction.
• Further research may be needed to refine the CF method, particularly for low-flow states.