Inspiratory-to-expiratory ratio during ventilation for idiopathic respiratory distress syndrome

We have studied the effects of changes in inspiratory-to-expiratory ratios (I/E ratios) on transcutaneous blood gases in a group of 30 infants receiving respiratory support for the idiopathic respiratory distress syndrome (IRDS). Following the use of a reversed I/E ratio (inspiration exceeding expiration), changes in oxygenation were very variable but improvements were seen most consistently in babies weighing greater than 1,750 g and less than 850 g. The use of reversed I/E ratios seemed less efficient than positive end-expiratory pressure in raising TcPO2 for the same increase in mean airway pressure. Changes from a 1:1 ratio to a normal I/E ratio, in which expiratory time exceeded inspiratory time by 50-100%, led to more marked and consistent falls in TcPO2. We conclude that a flexible attitude toward the use of I/E ratios should be adopted to avoid raising mean airway pressure needlessly.