COMPARISON OF CARDIAC-OUTPUT MEASUREMENT TECHNIQUES - THERMODILUTION,DOPPLER, CO2-REBREATHING AND THE DIRECT FICK METHOD

Simultaneously measured cardiac output obtained by thermodilution (TD) , transcutaneous suprasternal ultrasonic Doppler (DOP), CO2-rebreathin g(CR) and the direct Fick method (FI) were compared in eleven healthy subjects in a supine position (SU), a sitting position (SI), and durin g sitting exercise at a workload of 50 W (EX). The agreements between the techniques, two by two, were expressed as the bias calculated as t he averaged differences between the techniques. Precision was expresse d as the standard deviation of the bias. The overall agreement (bias+/ -precision) between TD, DOP and CR respectively and FI were 2.3+/-1.6, -0.1+/-1.4, and -0.2+/-1.1 1/min, TD overestimated cardiac output con sistently in SU, SI and EX. DOP was in-accurate during EX and agreed w ell with FI in SU and SI. CR agreed closely with FI in SI and EX, bur values were underestimated in SU. The overall agreement between DOP an d CR, respectively, and TD were 2.5+/-2.2 and 2.6+/-1.6 1/min. The ove rall agreement between DOP and CR was 0.1+/-1.6 1/min. In conclusion, TD overestimated cardiac output compared to the other techniques and r be poor agreement has to be taken into consideration especially in mea sures of low values. The precision of DOP and CR against FI seems to b e within clinically acceptable limits, and these methods may provide i nterchangeable alternatives to the invasive Fick method.