Thermodilution method overestimates low cardiac output in humans

Area of Science:

• Cardiovascular Physiology
• Medical Device Technology

Background:

• Cardiac output (CO) measurement is vital for managing critically ill patients.
• Thermodilution and Fick methods are commonly used to assess CO.
• Previous studies have shown discrepancies between CO measurement techniques.

Purpose of the Study:

• To compare cardiac output measurements between thermodilution and Fick methods.
• To investigate potential overestimation of cardiac output by thermodilution in low-flow states.

Main Methods:

• Compared 57 cardiac output measurements using thermodilution and Fick methods in 26 patients.
• Analyzed discrepancies in measurements, particularly in low output ranges (Fick < 3.5 L/min).

Main Results:

• Thermodilution values were higher than Fick values in all 16 cases with Fick outputs < 3.5 L/min.
• An average difference of 35% was observed when Fick values were ≤ 2.5 L/min.
• Findings suggest thermodilution overestimates true cardiac output in low output ranges, likely due to heat loss.

Conclusions:

• The thermodilution method may overestimate cardiac output in low-flow conditions.
• Heat loss is a probable cause for this overestimation.
• Clinical implications exist for patients with low output states where thermodilution is frequently used.