NEAR CONTINUOUS CARDIAC-OUTPUT BY THERMODILUTION

A new thermodilution method for frequent (near continuous) estimation of cardiac output, without manual injection of fluid into the blood, w as tested. The method utilizes a pulmonary artery catheter equipped wi th a fluid filled heat exchanger. The technique is based on cyclic coo ling of the blood in the right atrium and measurement of the temperatu re changes in the pulmonary artery. Using this technique, a new estima te of cardiac output can be obtained every 32 s. Cardiac output estima tes, obtained for a running mean of three measurements with this metho d, were compared to the mean of three conventional thermodilution meas urements. The measurements were obtained during short periods of stabl e respiration and circulation. In six pigs, we made 46 paired measurem ents of conventional thermodilution (TD) and near continous (TDc) ther modilution. The cardiac output (COTD) ranged from 2.4-13.7 l/min (mean 5.4 l/min). The best linear fit through the paired data points was CO TDc, = -0.57 +/- 1.01 COTD. The mean difference between the methods wa s -0.50 l/min (S.D. = 0.39). The mean coefficient of variation of repe ated measurements with the near continuous thermodilution was 3.6%. Co nsidering changes of more than 0.25 l/min to be significant, all chang es in cardiac output measured by conventional thermodilution were foll owed by the running mean of three near continuous thermodilution estim ates. This study demonstrates the feasibility of the new method to mon itor cardiac output, and to detect all changes greater than 0.25 l/min .