Cardiac output measurement by thermal dilution: reproducibility and comparison with the dye-dilution technique.

Cardiac output estimates by the principle of thermodilution (COth) was compared with dye-dilution estimates (COdye) in pigs. For COth estimates a Swan-Ganz 7 F floating thermodilution catheter and a 9500 Edwards Computer, were used. The COdye estimates were obtained by the apparatus constructed by Zijlstra and Mook. The effect of the thermistor position in the pulmonary artery on the COth estimates was also investigated. The reproducibility of COth was examined by duplicate determinations. Based on 101 simultaneous estimates of COth and COdye the correlation was found COth = 1.020 COdye + 0.2378, r = 0.971 for cardiac outputs between 0.65 l/min and 11 l/min. For 111 duplicate determinations of COth between 2 and 9 l/min the coefficient of variation was 4.74%. The thermistor position in the pulmonary artery had no influence on the COth estimates provided an undamped pressure curve could be monitored from the tip of the catheter. Cardiac output can thus be measured rapidly with good accuracy also for low values by means of a blindly inserted thermistor catheter positioned without x-ray control and a computer with digital display.