Cardiac output measurement using femoral artery thermodilution in patients

Abstract

This study was performed to assess thermal indicator loss between the pulmonary artery and the abdominal aorta after a single bolus injection in the right atrium, in order to validate cardiac output measurements from dilution curves recorded in an arterial vessel after central venous indicator injection. Thermal indicator dilution curves were simultaneously recorded in the pulmonary artery and the femoral artery after central venous injection of a 10 mL ice cold indocyanine-green dye solution. Cardiac outputs were determined on-line by identical cardiac output computers connected with thermistor catheters in the pulmonary artery catheter (CO PA) and the femoral artery (CO FA). Extravascular lung thermal volume was measured simultaneously. Paired dilution curves were measured on 804 occasions in 48 patients. The cardiac outputs correlate well (r = .94) with a least-square regression equation for the following data: CO FA = 0.97 CO PA ± 0.59 L/min. Mean femoral artery cardiac output was 7% greater than mean pulmonary artery cardiac output ( P < .001). We interpret this as being due to thermal indicator loss in passing through the lungs, left heart, and aorta. Thermal indicator loss is negatively correlated with cardiac output and extravascular lung thermal volume. We conclude that thermodilution measurements in a peripheral artery yield valid estimates of cardiac output with a 7% systematic overestimation due to thermal indicator loss.