Determination of cardiac output by the Fick method, thermodilution, and acetylene rebreathing in pulmonary hypertension

Assessment of cardiac output is an important part of the management of pati ents with pulmonary hypertension. The accuracy of the thermodilution techni que in patients with low cardiac output or severe tricuspid regurgitation h as been questioned. To address this issue, we simultaneously compared 105 c ardiac output measurements by the Fick method and thermodilution in 35 pati ents with pulmonary hypertension. Moreover, we evaluated the acetylene rebr eathing technique, a noninvasive method of determining cardiac output. The mean difference +/- 95% limit of agreement between thermodilution and the F ick method was +0.01 +/- 1.1 L/min. The mean difference +/- 95% limit of ag reement between acetylene rebreathing and the Fick method was -0.23 +/- 1.1 4 L/min. Neither the mean agreement nor the 95% limits of agreement of both thermodilution and acetylene rebreathing with the Fick method were affecte d by the presence of low cardiac output or severe tricuspid regurgitation. We conclude that thermodilution and acetylene rebreathing are useful tools for assessing cardiac output in patients with pulmonary hypertension, even in the presence of low cardiac output or severe tricuspid regurgitation.