Cardiac Catheterization Practice Test

During right heart catheterization, cardiac output is typically obtained using either thermodilution or the Fick principle. Thermodilution injects a known amount of cold saline into the right atrium and measures the resulting temperature change downstream in the pulmonary artery; analyzing the temperature-time curve provides the cardiac output. The Fick principle uses the patient’s oxygen consumption and the difference between arterial and mixed venous oxygen content: CO = VO2 / (arterial O2 content − mixed venous O2 content). This approach is especially helpful if thermodilution is unreliable or VO2 is directly measured.

Echocardiography can estimate cardiac output noninvasively, but it’s not the catheter-based method used during right heart catheterization. Nuclear perfusion imaging isn’t used to measure CO in the catheterization lab, and pulse contour analysis is a separate technique that isn’t the standard sole method during a right heart study.