Validation of transpulmonary thermodilution variables in hemodynamically stable patients with heart diseases

Transpulmonary thermodilution is recommended in the treatment of critically ill patients presenting with complex shock. However, so far it has not been validated in hemodynamically stable patients with heart disease.

We assessed the validity of cardiac output, global end-diastolic volume index (GEDVI), an established marker of preload thought to reflect the volume of all four heart chambers, global ejection fraction (GEF) and cardiac function index (CFI) as variables of cardiac function, and extravascular lung water index (EVLWI) as indicator of pulmonary edema in 29 patients undergoing elective left and right heart catheterization including left ventricular angiography with stable coronary heart disease and normal cardiac function (controls, n = 11), moderate-to-severe aortic valve stenosis (AS, n = 10), or dilated cardiomyopathy (DCM, n = 8).

Cardiac output was similar in controls, AS, and DCM, with good correlation between transpulmonary thermodilution and pulmonary artery catheter using the Fick method (r = 0.69, p < 0.0001). Left ventricular end-diastolic volume was normal in controls and AS, but significantly higher in DCM (104 ± 37 vs 135 ± 63 vs 234 ± 24 ml, p < 0.01). GEDVI did not differentiate between patients with normal and patients with enlarged left ventricular end-diastolic volume (848 ± 128 vs 882 ± 213 ml m^-2, p = 0.60). No difference in GEF and CFI was found between patients with normal and patients with reduced left ventricular ejection fraction. Patients with AS but not DCM had higher EVLWI than controls (9 ± 2 vs 12 ± 4 vs 11 ± 3 ml kg^-1, p = 0.04), while there was only a trend in pulmonary artery occlusion pressure (8 ± 3 vs 10 ± 5 vs 14 ± 7 mmHg, p = 0.05).

Cardiac output measurement by transpulmonary thermodilution is unaffected by differences in ventricular size and outflow obstruction. However, GEDVI did not identify markedly enlarged left ventricular end-diastolic volumes, and neither GEF nor CFI reflected the increased heart chamber volumes and markedly impaired left ventricular function in patients with DCM. In contrast, EVLWI is probably a sensitive marker of subclinical pulmonary edema particularly in patients with elevated left-ventricular-filling pressure irrespective of differences in left ventricular function.