The effect of amniotic fluid aspiration on pulmonary function in the adult and newborn rabbit

Abstract

Aspiration of uncontaminated human amniotic fluid was investigated in adult and newborn rabbits and compared with three other experimental groups: 10% meconium solution, saline, and sham-injected controls. Fluids were injected into the trachea of adult animals (4 or 6 ml/kg body weight), newborn vaginally-delivered animals (a mean volume of 8 ml/kg), and cesarean-delivered animals before their first breath (a mean volume of 11 ml/kg). In adult animals aspirating amniotic fluid or saline, arterial Po2 measured over a 24-h period showed a mean difference between groups of <5% for both 4 and 6 ml/kg. Meconium aspiration produced a greater depression in Po2 than amniotic fluid aspiration (a mean difference of 16 and 31% for 4 and 6 ml/kg, respectively) and animals aspirating meconium showed a deteriorating trend over 24 h, whereas animals aspirating amniotic fluid improved. One of eight adult animals aspirating amniotic fluid died versus four of five aspirating meconium. AH five animals aspirating saline 6 ml/kg survived. Lung weight and resting volume of adult animals aspirating amniotic fluid were not significantly different from animals aspirating saline or nothing. Lung pressure volume curves from adult animals aspirating amniotic fluid were nearly identical to controls. Histology showed significantly greater atelectasis in adult animals that received 6 ml/kg amniotic fluid than controls, but this was not different from saline. There was no association between the number of cells in amniotic fluid and arterial Po2 after aspiration or any other aspect of pulmonary function measured. Newborn rabbits aspirating human amniotic fluid were not significantly different from those aspirating saline and non-aspirating controls with respect to mortality, respiratory rates, lung weights, static deflation curves, chest radiographs, or lung histology. This was in marked contrast to the effects of aspiration of an equal volume of 10% meconium solution, which produced a mortality of 100%. We conclude that aspiration of human amniotic fluid is unlikely to be associated with specific lung disease. © 1983 International Pediatrics Research Foundation, Inc.