The aim of this study was to compare gas exchange and volume delivery during high frequency oscillation at two frequently used inspiratory:expiratory (I:E) ratios: 1:2 and 1:1, other oscillatory settings being kept constant. A group of 13 infants with respiratory distress syndrome, median gestational age 28 weeks (range 23-36) and postnatal age 1 day (range 1-8) were studied. At the I:E ratio of 1:1 compared to 1:2 the median paCO(2) was lower, P < 0.05 (30 mmHg, range 22-47 vs 34 mmHg, range 27-46) and the volume delivered higher, P < 0.01 (2.6 ml/kg, range 1.2-5.6 vs 2.0 ml/kg, range 1.0-3.9). There was no significant difference in oxygenation levels at the two I:E ratios. In a related in vitro study, changing the I:E ratio from 1:2 to 1:1 increased the mean airway pressure by a median of 8.6% (range 2.9-28.1%).
Conclusion: Routinely maintained longer expiratory than inspiratory times during high frequency oscillation should be discouraged.