A number of techniques have been recommended for the prevention of ventilator acquired pneumonia (VAP). These techniques - such as patient positioning, continuous sub-glottic suction of the secretions, selective decontamination of the digestive tract etc… - aim at prevent the inhalation of oro-pharyngeal contaminated secretions around the cuff of the tracheal tube used for connecting the patient to the machine. Their efficacy has been regularly challenged and they are still unable to suppress totally the occurrence of VAP. The cuff of the tracheal tube used for long-term MV in the ICU is most often a low pressure high volume polyvinyl chloride (PVC) cuff in order to adhere to a large surface of the tracheal wall without inducing ischemic lesions. Recent advances allowed industrial companies to provide us with 1) polyurethane cuffs and 2) cuffs with a conic shape, both potentially offering a better tightness against inhalation at least in VITRO and in animal models. The effect on the reduction of VAP incidence has been suggested by several pilot series. The aim of the present project is to assess the efficacy of four types of cuffs (PVC with a conic or a cylinder shape and polyurethane with a conic or a cylinder shape) to prevent tracheal colonisation. We shall measure both oro-pharyngeal and tracheal colonisation during the hours and days following intubation. This will be done in 600 ICU patients of four university affiliated centres from France and Tunisia divided in 64 cluster randomized groups. The results of this research will confirm (or not) the rationale to perform a larger study designed specifically to address the impact on VAP.