Impedance cardiography: the next vital sign technology?

Area of Science:

• Cardiovascular Physiology
• Critical Care Medicine
• Medical Monitoring Technology

Background:

• Cardiac output (CO) monitoring is crucial in critical care, particularly for post-cardiac surgery patients.
• Impedance cardiography (ICG) is a non-invasive method for CO estimation, with evolving generations of technology.
• Thermodilution (CO-TD) is a common, albeit invasive, method for CO measurement, often used as a reference standard.

Purpose of the Study:

• To assess the intramethod variability of the latest ICG monitor and thermodilution (CO-TD) for CO measurements.
• To compare the intermethod agreement between the latest ICG CO (CO-ICG) and CO-TD.
• To evaluate the performance of previous ICG CO equations (Kubicek, Sramek, Sramek-Bernstein) against CO-TD.

Main Methods:

• Prospective study conducted in a cardiovascular-thoracic surgery ICU.
• 53 post-coronary artery bypass graft patients underwent simultaneous CO measurements using the latest ICG monitor and CO-TD.
• 210 pairs of CO measurements were analyzed to compare different ICG equations and CO-TD.

Main Results:

• The latest ICG CO (CO-ICG) demonstrated significantly lower intramethod variability (6.3%) compared to CO-TD (24.7%).
• CO-ICG showed good agreement with CO-TD (r² = 0.658, bias = -0.17 L/min, precision = 1.09 L/min).
• Previous ICG equations (CO-K, CO-S, CO-SB) showed progressively better agreement with CO-TD than older methods, but less than CO-ICG.

Conclusions:

• The latest ICG technology provides less variable and more reproducible intrapatient CO measurements than CO-TD.
• CO-ICG is equivalent to the accepted average CO-TD in post-CABG patients.
• The newest ICG CO equation significantly improves agreement with CO-TD compared to predecessor equations.