Surfactant Metabolism during Hyperventilation of Newborn Lambs with Atrial Right to Left Shunts

Abstract

ABSTRACT. We studied the effect on surfactant metabolism of 8 h of mechanical ventilation at tidal volumes of 13 2 0.3 ml/kg and very high tidal volumes of 28 f 1.5 ml/kg, with and without added COz, in the presence of an atrial right to left shunt in 4-to 8-day-old lambs. Similarly aged, spontaneously breathing lambs were used as controls. Right to left atrial shunts were created by inflating a balloon in the right atrium after a Rashkind atrial septostomy, thus creating a stable, easily controlled atrial shunt. Radiolabeled surfactant phospholipid precursors were used to probe incorporation into and secretion of surfactant phosphatidylcholine, whereas intratracheally administered labeled natural surfactant was used to evaluate alveolar clearance. Protein leak from the vascular space to the lungs was measured using radioactive iodine-labeled albumins. At the end of the 8-h study period, tissue association of alveolar surfactant was significantly increased to 63% in the mechanically hyperventilated lambs as compared to 44% in those lambs mechanically ventilated but not hyperventilated (p < 0.05) and to 39% in the spontaneously breathing control animals (p < 0.05). No increased surfactant secretion or decreased compliance was detected with hyperventilation. However, the lambs had very large surfactant-saturated phosphatidylcholine pool sizes, and a large portion (50%) was already in the alveolar pool, even in the spontaneously breathing lambs. Precursor incorporation into saturated phosphatidylcholine was similar in all groups, and very low and comparable protein leaks were seen in the different groups of lambs. These experiments did not detect any adverse effects of 8 h of mechanical ventilation, large atrial shunts or mechanical hyperventilation on the surfactant system of newborn lambs. (Pediatr Res 25:83-88,1989) In neonates with persistent pulmonary hypertension, hyperventilation has been considered an essential part of the ventilatory support ( I ) . Suprasystemic pulmonary arterial pressures cause right to left shunts at the patent foramen ovale and ductus arteriosus levels which result in progressive hypoxemia. The goal of hyperventilation is to attain a critically low P a c o~ and alkaline pH which may promote reversal of the right to left shunt by decreasing pulmonary artery pressures to less than systemic levels (1). However, infants often become less responsive to the same

Corticosteroids and Fetal Intervention Interact to Alter Lung Maturation in Preterm Lambs

“…In the animals in which surgery was performed~7 d before treatment, large corticosteroid-mediated effects on postnatal pulmonary function were noted . Cortisol treatment improved compliance by 50%, Table I. newborn sheep (about 100 Ilmol/kg) (23). In contrast to the alveolar pools, the amount of Sat PC in the total lung in the 117-d cortisol animals was twice that of the other groups.…”

The Effect of Hypocapnia and Mechanical Pulmonary Stress on Lung Tissue in Newborn Lambs

“…In adult sheep decreased lung compliance was found as early as 6-12 h after onset of hyperventilation [16]. Alveolar saturated phosphatidyl pool sizes seem to be abundant in approximately 1-week-old lambs [26]. That finding might be the explanation for the absence of lung injury in our study, since we used newborn lambs.…”

“…Rider et al [26] hyperventilated newborn lambs for 8 h with diminished pulmonary blood flow pro duced by an atrial right-to-left shunt. These authors did not detect gross atelectasis, hem orrhage nor increased surfactant secretion or decreased compliance.…”