Effects of continuous bed rotation and prolonged mechanical ventilation on healthy, adult baboons

Objective: To study, in a model of prolonged mechanical ventilation, the role of continuous bed rotation on lung function and pathology. Design: Prospective animal study. Setting: Animal research laboratory. Subjects: Healthy adult baboons (Papio cynocephalus), anesthetized with ketamine, sedated, paralyzed, mechanically ventilated for 11 days, and monitored with pulmonary and peripheral arterial catheters. Interventions: Animals were divided into two experimental groups: a) mechanical ventilation alone (control, n = 7); and b) mechanical ventilation with continuous bed rotation therapy to 45°(continuous rotation group, n = 5). Mechanical ventilation was provided for 11 days with an FIO₂ of 0.21 and tidal volume of 12 mL/kg. Bronchoalveolar lavage was performed through a fiberoptic bronchoscope. Nursing care procedures, antacids, enteral feeding, and prophylactic antibiotics were administered. Measurements and Main Results: Measurements of hemodynamics, pulmonary functions, lung volumes, arterial blood gases, and chest radiographs were done daily. Bronchoalveolar lavage was performed at days 0, 7, and 11. There were no significant changes in hemodynamics, gas exchange, or pulmonary functions during the study period in either group. Microbiological surveillance cultures were negative in both experimental groups. In the control group after 7 days, six of seven animals developed patchy atelectasis; by day 11, two of seven animals demonstrated persistent radiologic abnormalities. Bronchoalveolar lavage neutrophils were significantly increased in control animals at days 7 and 11. Lung pathology in the control group showed areas of bronchiolitis, with surrounding bronchopneumonia in five of seven animals. None of the continuous rotation animals showed any radiologic or morphologic abnormalities. Conclusions: Prolonged mechanical ventilation in the control group resulted in atelectasis, increased concentrations of bronchoalveolar lavage neutrophils, and mild pneumonitis. These effects were not associated with changes in lung volumes, oxygenation, or hemodynamic parameters. Continuous bed rotation helped to prevent these abnormalities.