We appreciate the interest of Drs. Phillips and Perel in our recent article.1However, they seem to have focused on whether there exists a numeric equivalence between extravascular lung water (EVLW) measured by computed tomography tissue volume and the transpulmonary thermodilution method (EVLWTPT). Any such equivalence between these values is as much coincidence as anything else, because it has been shown by Kirov et al. 2that a species-specific correction is required to calibrate the EVLWTPTmeasurement to accurately reflect gravimetric EVLW. We used the unmodified values from the PiCCO® device (Pulsion Medical Systems, Munich, Germany) because no validated canine correction factors are available. However, because this correction is linear, we believed that the changes in EVLWTPTwould be reasonable to follow, and, as we described, the changes in each of these measures after lipopolysaccharide administration were very different. Our goal, however, was not to perform yet another validation of EVLWTPTbut to gain insight into the pathophysiologic mechanisms that might impact the reliability of the measured EVLWTPT. Phillips and Perel apparently agree that the EVLWTPTincreased after lipopolysaccharide while EVLW measured by computed tomography did not. Even if lipopolysaccharide administration caused an increase in the actual EVLW in the short time between administration and imaging, they offer no explanation as to why this was not evident on whole lung computed tomography imaging, which despite their objections is widely accepted as a sensitive and specific measure of lung mass.3,4On the basis of the changing perfusion distribution observed, we interpreted this divergence of the two measurements to reflect an acute change in the perfused thermal mass, resulting in an artifactual increase in the EVLWTPT.
Nonetheless, we share the enthusiasm of Phillips and Perel in the value of a bedside measurement of lung edema and look forward to careful studies examining its optimal use and effect on outcomes. We hope, however, that the data we presented will assist practitioners in the thoughtful interpretation of the information this monitor provides.
*Johns Hopkins Medical Institutes, Baltimore, Maryland. email@example.com