Do not Use Pulmonary Artery Catheter Measurements in Tricuspid Regurgitation
Dimitris Stefanidis MD, PhD
Ronald F. Sing DO
Most of the parameters obtained from pulmonary artery (PA) catheters are calculated rather than directly measured; only right atrial and pulmonary artery pressures can be directly measured. Many PA catheters use the method of thermodilution to calculate cardiac output (CO) indirectly. This method, however, is subject to a number of pitfalls that can occur during daily interpretation of PA catheter readings and invalidate measurements. Tricuspid valve regurgitation, low flow states, patient temperature, presence of intracardiac shunts, and volume of injected bolus can all interfere with accurate measurements.
Watch Out For
Thermodilution is a method of measuring blood flow. A cold electrolyte solution is injected through the proximal port of the PA catheter into the right atrium. The cold fluid mixes with blood in the right heart chambers and the cooled blood is ejected into the pulmonary artery, where it flows past a thermistor located at the distal end of the PA catheter. The changes in blood temperature over time recorded by the thermistor are used to create a temperature-time curve; the area under this curve is equivalent to the average cardiac output in the absence of intracardiac shunts. In the case of tricuspid regurgitation, the cold fluid is delayed in the right heart because of back-and-forth movement across the incompetent valve, thus leading to a prolonged thermodilution curve. This produces a falsely low cardiac output.