1166 EFFECTS OF LABOR AND TYPE OF DELIVERY ON DRAINAGE OF FETAL LUNG LIQUID IN RABBITS

Abstract

Published reports suggest that drainage of fetal lung liquid begins immediately at birth, usually is complete in 4-6 h, but is delayed by cesarean section (CS). To re-examine this process, we measured pulmonary blood volume (PBV), extravascular lung water (EVLW), and size of perivascular fluid cuffs in frozen lung sections of 152 full-term rabbits born vaginally or by CS. We killed the rabbits before they breathed or at varying intervals, up to 24 h, postnatally by immersion in liquid N2 after intraperitoneal barbiturate. Ten additional rabbits, killed before breathing, had CS after labor. CS rabbits (n=83) weighed 50 ± 7 g, vaginally-born (n=69) weighed 51 ± 8 g. Results: (1) a comparable increase in PBV after breathing in both groups; (2) EVLW significantly less (by 17%) in fetuses born vaginally, compared to those born by CS without labor, but no difference in EVLW for fetuses born either vaginally or by CS after labor; (3) no postnatal decrease in EVLW until 30-60 min of age irrespective of type of delivery; thereafter, decrease in EVLW over 24 h was similar for the 2 groups; (4) maximal perivascular cuffing at 30 min of age, virtually absent by 2-4 h after birth for both groups. Our results suggest that lung liquid content of fetal rabbits decreases during labor, but does not diminish further until 30-60 min after birth; a compliant perivascular tissue space accomodates excess fetal lung liquid until its later removal; and type of delivery has no effect on the pattern of postnatal lung liquid drainage.