Lung water and vascular permeability-surface area in newborn lambs delivered by Caesarean section compared with the 3-5 days-old lamb and adult sheep

Extravascular lung water and vascular permeability-surface area products were measured with a multiple indicator dilution method in five unanaesthetized newborn lambs 2 to 7 h following delivery by Caesarean section at a gestational age of 135-142 days. The indicators used were 51Cr-labelled erythrocytes, [125I] albumin, [3H] water and [14C] urea. Post-mortem determination of extravascular lung water and dry bloodless lung weight were also performed. The results were compared with previously obtained data in unanaesthetized 3-5 days-old lambs and adult sheep. Normalized to dry lung weight, extravascular lung water by both techniques was significantly higher in lambs after Caesarean section than in either the 3-5 days-old lambs or the adult sheep (P less than 0.05). (Indicator values = 3.9 +/- 0.2 (SEM) ml/g for Caesarean section lambs, 3.1 +/- 0.3 for 3-5 days-old lambs and 3.3 +/- 0.5 for adult sheep; post-mortem values were 6.12 +/- 0.28 g/g for after Caesarean section lambs, 4.07 +/- 0.26 for 3-5 days old lambs and 4.03 +/- 0.17 for sheep). Vascular permeability-surface area product for [14C] urea, computed by a mathematical model, was significantly higher (P less than 0.05) in lambs after Caesarean section than in adult sheep (0.18 +/- 0.02 compared with 0.10 +/- 0.03). In 3-5 days-old lambs the value was 0.16 +/- 0.04. It is concluded that, when normalized to dry lung weight, lung following Caesarean section delivery near the end of gestation. Adult values for lung water have been reached by the age of 3-5 days.

Pulmonary vascular response to prostacyclin in fetal lambs

Eighteen prostacyclin injections (19.4 +/- 1.5 micrograms/kg) were performed in five chronically instrumented, intact fetal lambs in order to study the effects on pulmonary blood flow. These resulted in a brief period of bradycardia followed by a more prolonged period of increased pulmonary blood flow. In this latter phase, pulmonary blood flow increased from a baseline value of 49 +/- 4 ml/(kg min) to 122 +/- 10 ml/(kg min). Systolic/diastolic pulmonary arterial pressure simultaneously fell from 73 +/- 2/48 +/- 1 to 68 +/- 2/42 +/- 1 mm Hg. Flow through the ductus arteriosus was unchanged and right ventricular output increased to account for the increased pulmonary blood flow. Thus, prostacyclin causes pulmonary vasodilation in intact fetal lambs and may participate in the control of fetal pulmonary blood flow and the circulatory adjustments to extra-uterine life.