1294 LUNG WATER IN VENTILATED, IMMATURE FETAL LAMBS

Abstract

The rate and mechanism of fetal alveolar liquid clearance and the change in extra-alveolar lung water was studied during the initial 4 hours of positive pressure ventilation in 15 exteriorized fetal lambs, 125-135 days gestation, with negative lung liquid bubble stability tests, and intact umbilical circulation. Alveolar liquid volume was calculated from dilution of ⁵⁷Co-cyanocobalamin mixed with alveolar after periods of ventilation. Extra-alveolar lung water was determined from wet/dry weights, corrected for residual alveolar liquid, at sacrifice. Alveolar liquid was rapidly absorbed, 71±6% in 15 minutes, > 90% in 1 hour. Large tracer solutes, ¹³¹I-albumin and ¹²⁵I-cytochrome C, were not retained in the alveolar space by lung epithelial sieving, but absorbed at the same rate of water. Rapid absorption of alveolar liquid was not associated with its retention in the lung. Wet/dry ratio was 4.3±0.3 at 1 hour and 4.5±0.3 after 2 hours. At 4 hours it was significantly greater, 5.5±0.4. Positive pressure ventilation of immature lambs produces a much more rapid initial absorption of fetal alveolar liquid than previously measured in spontaneously breathing mature lambs, > 90% in the 1st hour vs 25%. Molecular sieving of alveolar liquid solutes typical of term fetuses was absent. The expected accumulation of excess lung water in immature lungs occurred only after completion of clearance of fetal alveolar liquid from the lungs. The edema of immature lungs is not retention of fetal alveolar liquid in the lung but a later phenomenon and of defferent origin. (Supported by Grant HL22552).

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