Comparison of cardiac output measured by intrapulmonary artery doppler, thermodilution, and electromagnetometry

Abstract

A Doppler pulmonary artery catheter system (Doppler cardiac output monitor or DOPCOM) that continuously measures instantaneous and mean cardiac output was recently introduced. Because thermodilution (TD) flow measurements may not represent an adequate standard, the present study was designed to compare TD and DOPCOM cardiac output measurements with aortic electromagnetic (EM) flow in cardiac surgical patients. Twenty-one patients scheduled for elective coronary artery bypass grafting were enrolled in the study. Simultaneous measurement of cardiac output by all three methods was performed before cardiopulmonary bypass, after cardiopulmonary bypass with the aorta cannulated and volume intermittently infused, and after decannulation. Analysis of all data demonstrated fair TD and EM correlation ( r = 0.80), with minimal bias (0.03 ± 1.21 L/min) and a median absolute error of 0.53 L/min; DOPCOM and EM data showed moderate correlation ( r = 0.64), a bias of −0.61 ± 1.50 L/min, and a median absolute error the same as TD (0.51 L/min). However, distribution of DOPCOM values was heavily skewed by 3 patients in whom flow measurements immediately after cardiopulmonary bypass were markedly different between the DOPCOM and electromagnetometry, probably because of malposition of the Doppler transducers secondary to partial catheter withdrawal during bypass. Consistent with this theory was the finding that before CPB, the DOPCOM was significantly better than TD in predicting EM flow (median absolute error: DOPCOM, 0.12 L/min, and TD, 0.48 L/min; p = 0.04). Our data suggest that, in general, the DOPCOM shows similar precision to TD for predicting EM flow measurements, although the DOPCOM may underestimate actual flow. However, when optimal position of the DOPCOM catheter is maintained, the device is significantly more precise than TD and does not underestimate flow. Furthermore, the instantaneous on-line data provided by the DOPCOM may potentially provide the basis for beat-to-beat assessment of the pulmonary circulation and right ventricular function.