Thermal indicator sampling and injection sites for cardiac output

¹ Departments of Physiology and Internal Medicine, State University of Iowa College of Medicine, Iowa City, Iowa

The effects of indicator sampling and injection sites on estimation of cardiac output by the thermal dilution method were investigated in dogs. Dilution curves were recorded simultaneously with thermistors in the aortic arch and carotid or femoral artery after injection of indicator into the right atrium. The outputs calculated from carotid and femoral curves were higher than those from aortic curves. Nevertheless, the carotid and femoral arteries were considered satisfactory sampling sites because it was possible to predict aortic values from peripheral curves with a small range of error. The effect of indicator injection sites was studied by comparing outputs calculated from aortic curves after alternate injections into the right atrium and external jugular vein. The outputs calculated after jugular injections were higher. The external jugular vein was considered to be a less desirable injection site because the correlation between aortic values obtained after injections into the two sites was relatively low, and the predictability of one value from the other was not good.