Errors in estimating lung liquid volume in fetal lambs when using radiolabeled serum albumin and blue dextran

Abstract

Fetal lung liquid volume is usually determined by using radio-iodinated serum albumin (RISA) or blue dextran (BD) as volume tracers. We tested the reliability of both tracers at 124 (G124) and 142 days of gestation (G142; term = G147) when the labels were employed simultaneously. We measured the proportion of label bound reversibly to the lung, or apparently lost from the lung compartment, by washing out the lung with saline and 5% albumin. At G124, volume estimates with the two labels were similar. At G142, the volume estimate with BD (36.3 +/- 8.7 ml/kg of body wt) was higher (P < 0. 05) than with RISA (22.3 +/- 3.5 ml/kg). This difference resulted from reversible binding of BD, because 5% albumin washout released 38.5 +/- 4.0% of the BD added at the start of the experiment but a lesser amount of RISA (9.8 +/- 0.7%; P < 0.05). At G142, when RISA was used alone, its reversible binding was 1.3 +/- 0.2%. Background absorbance increased during experiments, giving rise to an apparent increase in BD concentration. We conclude that RISA is an effective tracer for lung liquid volume determination in the fetal lamb, whereas our findings of substantial epithelial binding of BD and large changes in background absorbance demonstrate that, under the conditions of our experiments, BD is a poor tracer close to term.

Estimation of lung liquid production in fetal sheep with blue dye dextran and radioiodinated serum albumin

“…In general, our data suggest that BDD is an acceptable indicator for studying fluid movements in fetal lungs, in at least partial disagreement with Pfister et al (31). However, it is difficult to compare methods from different laboratories.…”

“…It has been suggested that volumes might be affected by an unexplained jump in optical density of lung liquid between the first, "blank" sample and later samples, a jump that slowly subsided over the next hours (31). The significance of this effect is difficult to assess.…”

“…It is sometimes stated, or implied, that BDD has a high affinity for proteins and that this could complicate its use in dye-dilution studies (31). This is not strictly true.…”

“…BDD formed a second check on results obtained by RISA, and, in our careful studies of fetal sheep, the two were used together (5). However, recent reports by Pfister et al (31) have suggested that although BDD worked well in younger fetuses, it was in some way sequestered in those of 141 days of gestation, relatively close to term. Therefore, BDD was considered less reliable than RISA, even though it was already known that both albumin and RISA could escape the lungs and therefore did not satisfy the strictest requirements for indicator-dilution studies.…”

Relationship of Ultrafiltration and Anastomotic Flow in Isolated Rat Lungs

“…of the FITC-moiety or adhesion to protein lining the vasculature. Similar changes in the concentrations of other indicators such as Evans blue and methylene blue have been observed and it has been suggested that reduction or protein binding by the endothelium is responsible for this phenomenon (1,5,6,16,20). The actual causes for small losses of Evans blue from the vasculature in some of these studies remain uncertain.…”