In vivo validation of the thermal-green dye technique for measuring extravascular lung water

Assessment of extravascular lung water (EVLW) is imprecise in vivo, yet of both clinical and investigative relevance in patients with cardiac disease. Recently, a double-indicator method using thermal-green dye has been proposed as a nondestructive technique for in vivo quantification of EVLW. In our 5-yr study, indocyanine green dye was used as the intravascular indicator and heat as the diffusible indicator in 44 control dogs, 74 dogs administered intravenous oleic acid, 63 dogs in whom left atrial pressure was altered with a left atrial balloon, and 31 dogs with low-output cardiac failure (electrical shock and complete heart block). In these animals, in vivo measures of EVLW correlated closely with standard gravimetric techniques (r = 0.87, p less than .001), although the indicator dilution technique tended to underestimate actual lung water at higher volumes. In an additional 26 dogs, fluid (lactated Ringer's solution) was administered directly into a distal pulmonary airway, producing alveolar rather than interstitial edema. In these animals, as the infused volume was increased, the thermal technique underestimated consistently the actual amount of infused fluid. Nonetheless, we conclude that in most clinical and experimental situations where moderate changes in lung water are anticipated, this technique can provide reasonable estimates of extravascular fluid accumulation.