Effect of the degree of tricuspid regurgitation on cardiac output measurements by thermodilution

Objective: To determine the relationship between the degree of tricuspid regurgitation (TR) and accuracy of cardiac output measurement by thermodilution in mechanically ventilated patients. Design and setting: Prospective observational study in a 20-bed general intensive care unit in the university hospital. Patients: We examined 27 patients (not undergoing cardiac surgery): 8 with no or 1st degree TR, 9 with 2nd degree, and 10 with 3rd degree TR. Interventions: All patients were measured twice using simultaneously transesophageal echocardiography and pulmonary artery catheter for cardiac output. Measurements and results: Continuous Doppler measurements were taken in the left ventricular outflow tract at the level of the aortic valve. Cardiac output was calculated by multiplying the velocity-time integral by aortic valve area and heart rate. Simultaneous pulmonary artery catheter measurements were taken averaging the results of the three 10-cc boluses of iced saline. The difference between the methods was 0.5+/-1.1 l/min (mean +/- 2 SD) in patients with no or 1st degree TR (r=0.96), 0.8 2.0 l/min in those with 2nd degree TR (r=0.92), and 1.9+/-2.3 l/min in those with 3rd degree TR (r=0.69). Conclusions: A high degree of TR is associated with underestimation of cardiac output measured by thermodilution.