Principal endpoint(s) : quantitative assessment of bacterial colonization in the oro-pharyngeal (above the cuff) and tracheal (below the cuff) secretions at 2 hours (H2), 1 day (D1), D2 and D3 after intubation. The collection of the secretions above and below the cuff will allow to document the origin of the tracheal bacteria. The bacterial quantity at each sampling will be compared between the patients groups to establish the role of the cuff in the antibacterial protection of the lower airway.