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

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 less than 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. All 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.(ABSTRACT TRUNCATED AT 250 WORDS)