Limitations of volumetric indices obtained by trans-thoracic thermodilution

Transthoracic thermodilution (TTT) measures cardiac output without the need for right heart catheterization. In addition, two volumetric hemodynamic indices have been derived from the mathematical analysis of the TTT curve: the global end diastolic volume (a quantitative measure of cardiac preload) and the extravascular lung water volume (a quantitative measure of pulmonary edema). Despite the undeniable appeal of these two novel parameters, uncertainty exists regarding both the validity of their mathematical derivation and their physiological significance. This concise review attempts to discuss such concerns.