[Important physiological considerations in artificial respiration and reanimation of newborn infants]

The methods used for ventilation of the neonate shold be based upon consideration of the physiological changes which occure in the lungs and circulation at birth of the normal infant. Three important changes must be taken into consideration. The first is the formation of a residual volume of alveolar gas, the second the resorption of pulmonary fluid and the third a decrease in pulmonary vascular resistance, upon which is dependent the change from foetal circulation to that of the neonate. To begin insufflation of foetal lungs it is necessary to use a pressure of between 20 and 30 cm H2O. After the first insufflation, a good deal of air remains in the lungs, even during expiration, as long as pulmonary "surfactant" is present. In the absence of the latter, residual pressure at the end of expiration is necessary in order to avoid the lung emptying itself of air. The resorption of pulmonary liquid from the alveolar spaces into the blood is dependent upon a change in the permeability of the alveolar epithelium, which renders possible the rapid passage of water via the channels which open, probably between the epithelial cells, and this change is dependent upon an expansion of the lungs by a pressure of between 35 and 40 cm H2O. Dilatation of the pulmonary vessels depends in part upon an increase in partial pressure of oxygen and a fall in carbon dioxide in the environment of the pulmonary arterioles, and in part upon mechanical changes brought about by the movements of ventilatation.