Comparison of two closed systems for thermodilution cardiac outputs.

The authors used an in vitro flow system to evaluate the sources of error in a previously described closed system thermodilution method for cardiac output determinations. Cardiac outputs were overestimated by as much as 49% because the injectate warmed as it was drawn through the connecting tubing. Submerging the tubing in the ice bath prevented this problem. The authors also evaluated a new closed system thermodilution cardiac output method. The method employed a bypass line and a spring loaded autosyringe which enables the user to flush the system with cold fluid, thereby ensuring accurate injectate temperatures. Cardiac output determinations with this method were as accurate as those obtained with a CO2 powered injector. Additionally, this method is easy to use, accommodates injection volumes of 1-10 ml, and is inexpensive.