REPRODUCIBILITY OF THERMODILUTION CARDIAC-OUTPUT DETERMINATION IN CRITICALLY ILL PATIENTS - COMPARISON BETWEEN BOLUS AND CONTINUOUS METHOD

Objective. A semi-continuous thermodilution method (CCO) was recently developed to measure cardiac output with less risk of bacterial contam ination, fluid overload, and user-induced errors than the classical bo lus technique (BCO). Previous comparison between these two methods sho wed negligible bias. However, large limits of agreement suggest that t he two methods are not interchangeable. We hypothesized that this poor agreement may be due to differences in reproducibility. Methods. In 2 3 critically ill patients, 369 paired measurements of CCO and BCO were compared (range of cardiac outputs: 2.8 to 16 L/min). The reproducibi lity of BCO and CCO methods was evaluated on a sample of 205 and 209 d eterminations, respectively. Results. The comparison between the CCO a nd the BCO methods confirmed previous results: i.e., small bias (-0.39 L/min) and large limits of agreement (-2.06 to +1.28 L/min). Reproduc ibility showed no bias for either the CCO or the BCO method. Limits of reproducibility agreement between repeated determinations were approx imately 50% less for CCO than for BCO method: respectively -0.87 to +0 .82 L/min for the CCO method and -1.56 to +1.37 L/min for the BCO meth od. Consequently the threshold necessary to ascertain that the differe nce-between two measurements was not due to the internal variability o f the method (3 x SEM) was 0.39 for the CCO method and 0.75 L/min for the BCO method. Conclusion. Differences in reproducibility may explain the poor agreement between the CCO and BCO methods. The better reprod ucibility of the CCO method allows the detection of smaller variations in cardiac output and suggests the superiority of this new method.