Per-protocol analysis
The per-protocol population comprised 42 (31.1%) patients of the intervention group who spent > 2 h in the prone position each day and the 131 (99.2%) patients of the usual care group who never laid prone. The treatment failure rate was 7.1% in the prone position group and 13.0% in the usual care group (aOR 0.71, 95% CI 0.18–2.77) (in Additional file 