Effects of positive end-expiratory pressure on hyaline membrane formation in a rabbit model of the neonatal respiratory distress syndrome.

Sixteen rabbits were anaesthetized and subjected to saline lavage of the lungs to produce surfactant deficiency. This resulted in an arterial oxygen tension of less than 12 kPa on 100% inspired oxygen and an inflection point on the pressure-volume curve at a pressure of 8-12 mmHg. After lavage the animals were randomly assigned to receive either conventional mechanical ventilation (CMV) with a positive end-expiratory pressure (PEEP) of 1-2 mmHg (group I - low PEEP) or CMV with PEEP equal to the inflection point pressure (group II - high PEEP). Mean airway pressures were kept at 14-16 mmHg in both groups by increasing the inspiratory:expiratory time ratios in the low PEEP group. The 5-h protocol was completed by 4 animals in group I and 6 animals in group II, early death usually being associated with a metabolic acidosis. On 100% oxygen, the mean PaO2 at 2-h post-lavage was 15.2 +/- 8.3 kPa in group I and 39.6 +/- 21.8 kPa in group II. Group I had much lower end-expiratory lung volumes (3.0 +/- 1.5 ml above FRC) than group II (34.9 +/- 12.2 ml above FRC). Histological examination of the lungs revealed significantly less hyaline membrane formation in group II (p = 0.001). Thus, the prevention of alveolar collapse by the use of high PEEP levels appears to reduce lung damage in this preparation.