Supplementary Material for: High-Frequency Oscillatory Ventilation with Low Oscillatory Frequency in Pulmonary Interstitial Emphysema

Background: Pulmonary interstitial emphysema (PIE) is a common respiratory illness in preterm infants associated with significant morbidity and mortality for which the ventilatory management is imperfect. Objectives: To evaluate the impact of high-frequency oscillatory ventilation (HFOV) with a low oscillatory frequency and thus prolonged expiratory time in preterm infants with severe PIE. Methods: In a retrospective cohort study, preterm infants ≤30 weeks' gestation with radiological findings of severe PIE, and either high FiO₂ or persistent respiratory acidosis were studied if managed on HFOV with a low frequency (5-6 Hz, inspiratory time 30%) for >24 h. Trends in physiological and ventilatory parameters were examined over the first 72 h, radiological changes noted, and in-hospital outcomes ascertained. Results: 19 cases were identified and analysed in two groups: 14 with bilateral and 5 with predominantly unilateral disease. After transition to low-frequency HFOV, physiological responses were seen in both groups, in particular a rapid and sustained improvement in oxygenation in the bilateral group (mean (SD) alveolar-arterial oxygen difference at baseline: 404 ± 206 mm Hg; 4 h post-transition: 262 ± 181 mm Hg; 72 h: 155 ± 74 mm Hg; p = 0.0003). This occurred following a reduction in mean airway pressure (mean (SD) baseline: 14 ± 3.9 cm H₂O; 72 h: 12 ± 2.9 cm H₂O; p = 0.011). In the unilateral group, radiological resolution of PIE was observed on re-inflation following collapse of the affected lung. Overall, 15 infants survived, including 10 of the bilateral cases (71%), and all of the unilateral cases. Conclusion: HFOV with a low oscillatory frequency may afford benefit in preterm babies with severe PIE.