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.