A studied realized by our group (EPO2-PV) evaluated the effect of three positions (Reverse Trendelenburg, beach chair and supine) and two ventilation strategies (spontaneous ventilation with or without positive pressure) on morbidly obese FRC in laboratory. The results showed a statistically significant difference on the FRC after a pre-oxygenation with positive pressure compared with the pre-oxygenation without positive pressure, and this regardless of the position. Moreover, for both ventilation strategies, results demonstrated a statistically significant superiority between the FRC obtained after pre-oxygenation in reverse Trendelenburg compared with the beach chair and the supine position. No improvement has been shown with the beach chair position.