ObjectiveTo explore the role of the horizontal orientation of endotracheal tube and neck on bacterial colonization of the respiratory tract in anesthetized sheep on mechanical ventilation, without use of antibiotics.DesignProspective animal study.SettingNational Institutes of Health research laboratory.SubjectsAnesthetized, paralyzed, and ventilated sheep.InterventionsSheep were randomized into five groups and managed as follows: Group IS contained sheep that were not intubated and were immediately killed. Group HU4 contained six sheep that were mechanically ventilated for 4 hrs, with head and endotracheal tube elevated 30 degrees from horizontal. Group HU72 contained seven sheep that were prone, mechanically ventilated for 72 hrs, and managed the same as group HU4. Groups G and Gf each contained seven sheep that were prone on a lateral body rotation device, mechanically ventilated for 72 hrs, with neck and endotracheal tube horizontal. Group Gf received nasogastric enteral feeding.Measurements and Main ResultsAt the end of the study, sheep were examined postmortem, and a total of 11 tissue samples were taken from the trachea, the five lobar bronchi, and the five lobar parenchyma, for qualitative and quantitative culture. Group HU72 had significant decrease in Pao2/Fio2and heavy bacterial colonization in all sheep. Groups G and Gf retained excellent lung function; lung bacterial colonization was no different from the IS group.ConclusionsThe horizontal orientation of the endotracheal tube and neck, through lateral body rotation, showed no altered airway colonization and maintained excellent gas exchange and lung function in our animal model.