Hemodynamic and ventilatory effects of stepwise head-of-bed elevation in acute respiratory distress syndrome patients...

High-flow nasal cannula (HFNC) therapy is widely utilized in patients with acute respiratory distress syndrome (ARDS) due to its significant clinical efficacy. While guidelines exist for positioning during invasive ventilation, the optimal head-of-bed (HOB) elevation for ARDS patients receiving HFNC is unknown, balancing recruitment benefits against risks like hemodynamic compromise. Therefore, this study aimed to evaluate the short-term effects of stepwise HOB elevation (15°, 30°, 45°, and 60°) on oxygenation, ventilation distribution, and hemodynamics in ARDS patients receiving HFNC therapy.

This prospective, single-center, sequential physiological study enrolled 20 adult ARDS patients [Berlin definition; arterial oxygen partial pressure (PaO₂)/fraction of inspired oxygen (FiO₂) 100-300 mmHg] receiving HFNC therapy. Using a fixed sequence (non-randomized), HOB elevation was adjusted to 15°, 30°, 45°, and 60°, with each position maintained for 30 minutes. The primary outcomes were the PaO₂/FiO₂ (P/F) ratio and the proportion of ventilation in dependent lung regions [region of interest (ROI)3+4] measured by electrical impedance tomography (EIT). Comparisons were performed using the Wilcoxon signed-rank test with Bonferroni correction.

The mean P/F ratios (mmHg) at each angle were: 15°: 160.00±59.66, 30°: 162.42±53.36, 45°: 176.66±70.92, 60°: 184.24±68.63. Significant pairwise differences (P<0.05, adjusted) were observed for 15° vs. 45°, 15° vs. 60°, 30° vs. 60°, and 45° vs. 60°. The proportion of ventilation in dependent regions (ROI3+4, %) was: 15°: 44.7±9.1, 30°: 46.2±10.3, 45°: 46.8±9.8, 60°: 48.4±11.2, with significant differences between 15° vs. 45° and 45° vs. 60°. Hemodynamic parameters remained stable across all positions.

In this sequential study, stepwise HOB elevation to 45° and 60° was associated with significantly higher P/F ratios and a favorable redistribution of ventilation toward dependent lung regions compared to lower angles, without apparent hemodynamic compromise in the short term. These physiological findings suggest potential benefit but require validation in randomized studies to account for temporal and order effects.