Near continuous cardiac output by thermodilution

A new thermodilution method for frequent (near continuous) estimation ofcardiac output, without manual injection of fluid into the blood, was tested.The method utilizes a pulmonary artery catheter equipped with a fluid filledheat exchanger. The technique is based on cyclic cooling of the blood in theright atrium and measurement of the temperature changes in the pulmonaryartery. Using this technique, a new estimate of cardiac output can be obtainedevery 32 s. Cardiac output estimates, obtained for a running mean of threemeasurements with this method, were compared to the mean of three conventionalthermodilution measurements. The measurements were obtained during shortperiods of stable respiration and circulation.In six pigs, we made 46 paired measurements of conventional thermodilution(TD) and near continous (TDc) thermodilution. The cardiac output(CO TD) ranged from 2.4–13.7 l/min (mean 5.4 l/min). Thebest linear fit through the paired data points was CO TDc =–0.57 + 1.01 CO TD. The mean difference between themethods was –0.50 l/min (S.D. = 0.39). The mean coefficient of variationof repeated measurements with the near continuous thermodilution was3.6%.Considering changes of more than 0.25 l/min to be significant, all changes incardiac output measured by conventional thermodilution were followed by therunning mean of three near continuous thermodilution estimates.This study demonstrates the feasibility of the new method to monitorcardiac output, and to detect all changes greater than 0.25 l/min.