Effect of helmet bilevel positive airway pressure on oxygenation in lateral and prone positions in mild-to-moderate acute respiratory distress syndrome: A fixed-sequence crossover trial

Background and Aim: To evaluate the effect of helmet bilevel positive airway pressure (helmet) on oxygenation in patients with moderate acute respiratory distress syndrome (ARDS) across body positions. Methods: This is a prospective, single-center, fixed-sequence crossover study. Adults with ARDS and baseline partial pressure of oxygen in arterial blood/fraction of inspired oxygen ratio (PaO 2 :FiO 2 ) of 150–300 received helmet-BiPAP and were assessed sequentially: supine → lateral → return to supine → prone → final supine. Primary outcome was a change in PaO 2 :FiO 2 in lateral and prone positions versus the preceding supine measurement. Secondary outcomes included PaO 2 :FiO 2 and respiratory rate changes after resupination and patient comfort. Results: Fifty-four subjects were enrolled; 48 received helmet-BiPAP and were analyzed (median age 42.5 years; baseline PaO 2 :FiO 2 176 ± 28 mmHg). A significant improvement in oxygenation was observed between supine and lateral position, with an increase in PaO 2 :FiO 2 (mean difference 19.3; 95% confidence interval 3.1–35.5; P = 0.021), and between supine and prone position (mean difference 32.4; 95% CI 15.4–49.5; P < 0.001). After resupination from the lateral position, PaO 2 :FiO 2 remained unchanged, whereas a decline occurred after resupination from the prone position (mean difference − 17.8 mmHg; 95% CI − 33.2 to − 2.4; P = 0.025). Respiratory rate remained stable across positions. Most patients reported acceptable comfort across positions, and comfort scores did not differ significantly across positions. Conclusion: In patients with moderate ARDS, helmet-BiPAP improved oxygenation across positional changes, with the greatest improvement observed in the prone position. Oxygenation gains diminished after return to supine from prone positioning but were largely maintained following lateral positioning. Lateral positioning may represent a feasible alternative during helmet-BiPAP for patients unable to tolerate prone positioning.