Methods for improving oxygenation in infants mechanically ventilated for severe hyaline membrane disease.

Methods for improving oxygenation in infants mechanicaily ventilated for severe hyaline membrane disease. The effect on arterial blood gas tensions, aortic blood pressure, and intra-oesophageal pressure of altering inspiration: expiration ratio and pressure during expiration was investigated in 9 infants being treated by mechanical ventilation for very severe hyaline membrane disease. The results showed that the use of a long inspiratory phase and a positive expiratory pressure acted synergistically to reduce alveolar-arterial oxygen difference and estimated right-to-left shunt: this reduction was proportional to mean airway pressure. The usefulness of a positive expiratory pressure in raising arterial oxygen tension was limited by its effect in causing alveolar hypoventilation. No adverse effects on the circulation due to the application of high mean airway pressures were detected. The principal abnormality in hyaline membrane disease (respiratory distress syndrome of the newborn) is deficiency of pulmonary surfactant which causes alveoli to collapse during expiration (Avery and Mead, 1959). Recent work by Gregory et al. (1971) and others (Chernick and Vidyasagar, 1972) has shown that arterial oxygenation can be substantially improved when the alveoli are held open by allowing the infant to breathe spontaneously against a continuous positive transpulmonary pressure. Nevertheless, the most severely affected infants still need mechanical ventilation (Swyer et al., 1973). Many infants ventilated for hyaline membrane disease have in the past died from bronchopulmonary dysplasia (pulmonary fibroplasia) which is probably caused by at least two factors: mechanical trauma to the lung from the use of high peak airway pressures We have therefore tried to find means for ventilating the infants at comparatively low peak airway pressures and at oxygen concentrations reduced as far as possible below 100%. It was shown in a previous study (Reynolds, 1971) that when using a constant pressure generator (Mushin et al., 1969) the best arterial oxygen tension was obtained with a slow respiratory frequency (30/min), and that arterial oxygen tension could be improved without increasing peak airway pressure by using a very long inspiratory phase (an inspiration: expiration ratio of 2:1 or more). This manoeuvre had no effect on arterial carbon dioxide tension or aortic blood pressure. In 1970, Llewellyn and Swyer presented preliminary evidence that the use of a positive pressure in expiration was also effective in raising the arterial oxygen tension of infants mechanically ventilated for hyaline membrane disease. The purpose of the present investigation was to find out which of the two manoeuvres (a …