Comparison of cardiac output measurement by continuous thermodilution with electromagnetometry in adult cardiac surgical patients

A pulmonary artery catheter (PAC) capable of continuous cardiac output (CCO) determination by thermodilution has recently been introduced. The purpose of this study was to compare CCO with two other methods of cardiac output (O_t) determination: electromagnetometry (EM) and standard bolus thermodilution cardiac output (BCO). Following median sternotomy and pericardiotomy, an EM ring probe was placed around the ascending aorta in 25 adult cardiac surgical patients and connected to an EM flowmeter interfaced with a calibrated strip recorder. Measurements were obtained over a 15- to 20-minute interval during a period of stable EM-determined O_t prior to initiation of cardiopulmonary bypass and in the absence of surgical stimulation. The CCO system averages O_t over a 3-minute interval, updating the measurement every 30 seconds. Cardiac output determined by the CCO system was compared with EM O_t averaged from the prior 3-minute period and with BCO obtained immediately after changing the Ot monitor from the continuous to bolus mode. Compared with EM, the bias for CCO was -0.48 L/min, precision 0.56 L/min, and the limits of agreement 1.12 L/min. Bias, precision, and limits of agreement of CCO compared with BCO were 0.41, 0.82, 1.64 L/min, respectively. Correlation between EM and CCO was r = 0.80 and between CCO and BCO r = 0.64. Cardiac output determined by CCO was within 10% of the EM determination for 37 measurements, between 10% and 20% for 17, and greater than 20% for 7 measurements. Within the limitations of thermodilution cardiac output measurement, the level of accuracy demonstrated for the CCO system compared with EM-determined Qt suggests that CCO is a clinically useful methodology.