Fluid volume balance between pulmonary intravascular space and extravascular space in dogs

We aimed to study the agreement of estimates of the pulmonary blood volume by the double indicator dilution method and the direct destructive method and the fluid volume balance between the pulmonary intravascular and extravascular spaces. We employed the double indicator dilution method using heat and indocyanine green, with a single injection (into the right atrium) and double sampling technique, that is from the pulmonary artery trunk (PAT) and the aortic root (Ao). With this method, we simultaneously determined the pulmonary extravascular water volume (PEWV), defined as the extravascular lung thermal volume estimated in Ao (LTVAo), and the pulmonary blood volume (PBV) from PAT to the left atrium (LA) (PBVPAT-LA). Dogs were divided into groups: a group without intervention (n = 16), a group loaded with dextran (n = 12) and a group loaded with alloxan (n = 7). When all groups were included, PBVPAT-LA (ml/kg) = 1.02 X PBVdirect(g/kg) + 0.96, n = 35, r = 0.83 where PBVdirect means the blood contents from the pulmonary artery bifurcation to the pulmonary vein measured by the direct destructive method. We substantiated the validity of the use of the double indicator dilution method. In studying the fluid volume balance, based on the results of the direct destructive method, the pulmonary intravascular-extravascular fluid volume ratio (intra/extra) was 1.3 +/- 0.3 (mean +/- SD) in the control state, implying that the interstitium in the lung is relatively "dry". As overt pulmonary edema developed by dextran infusion, the ratio exponentially decreased to 1.0 +/- 0.1 (p less than 0.01). The behavior of the fluid volume balance in question (intra/extra), studied with the double indicator dilution method, was essentially similar to that analyzed by the direct destructive method.