Study Objective: To compare cardiac output (CO) as measured by the arterial thermodilution technique using only a central venous catheter and an arterial catheter inserted into the axillary artery, with conventional CO measurement with thermodilution using a pulmonary artery (PA) catheter (PAC).

Design: Prospective clinical study in which each patient served as his/her own control.

Setting: General ICU of a large tertiary-care teaching hospital.

Patients: 22 patients who required invasive hemodynamic monitoring in the ICU.

Interventions and Measurements: CO measurements made using the PAC (COpa) were compared to bolus arterial thermodilution measurements (COax). The significance of acute changes in the continuous CO measurements during acute hemodynamic episodes was observed.

Main Results : The correlation between the two techniques (COpa and COax) was R² = 0.82. There was a tendency for 5% overestimation of COpa by the COax. The SEM% (SEM/average CO) for COax and COpa was 2.6% and 3.2%, respectively. The bias between measurements was 0.27 ± 0.67 L/min, and the limits of agreement (mean difference ± 2 SD) from minus 1.07 L/min to 1.63 L/min.

Conclusions: In critically ill patients, in whom the measurement of CO is required, arterial thermodilution, using a central vein and the axillary artery is accurate and reproducible.