To the Editor,

Dr. Lazaridus has presented a great review of advanced hemodynamic monitoring (AHM) [1]. Significant caution though must be used in accepting the accuracy of any noninvasive cardiac output methodology. The FDA 510 K approval process is not very rigorous and the comparison of noninvasive to invasive cardiac output (CO) is not done over a very large range of loading and unloading conditions. Hadian et al. [2] showed that FloTrac as well as other noninvasive CO devices showed widely varying results as compared to thermodilution (TD) CO and more importantly could trend in different directions under different loading conditions. The differences were in a range where therapy choices could be affected; possibly adversely. This type of testing is more clinically relevant and rigorous than the methodology used by Mutoh et al. [3] which assessed effects of volume loading but not that of vasoactive or inotropic drips. We have evaluated another noninvasive CO device in our unit, Cheetah, which measure CO by assessing changes in thoracic impedance and often found results diverging significantly from TD CO (unpublished data). In addition one of the statements “The ultimate goal of volume expansion is augmentation of stroke volume …” may not be completely accurate. There is evidence that excess volume expansion may worse renal failure and increase mortality in the setting of sepsis [4, 5]. The fact that the patient is fluid responsive as evidenced by passive leg raise (PLR) test does confirm that the patient is not on the flat portion of the Frank-Sterling curve. However since cardiac output is not necessarily the goal endpoint of fluid resuscitation and excess fluid can cause harm, further data is needed before accepting results of PLR as a clinical volume resuscitation endpoint.