Objective: To ascertain whether the locations of ventilator-induced lung injury (VILI) are influenced by body position.
Design: Randomized prospective short-term study.
Setting: Animal laboratory at a university school of medicine.
Interventions: Twelve white rabbits were mechanically ventilated in IMV mode with an infant ventilator (V.I.P. Bird, Bird Products, Palm Springs, Calif., USA). Based on the results of a preliminary study to determine the ventilator settings at which the lungs of rabbits were injured within 5 h in the supine position, the ventilator was set at F(I)O2 0.21, at a rate of 30/min, T(I) 0.6 s, peak inspiratory pressure 30 cm H2O, inspiratory flow 10 l/min with no applied positive end-expiratory pressure (PEEP). Six of the animals were tested in the supine position and the other six in the prone position. Respiratory gases were measured and CT scanning was performed every 30 min. The animals were ventilated for 5 h or until pulmonary parenchymal opacification was detected. The lungs were divided into three areas from apex to base and three levels from ventral to dorsal, and the location of opacification was ascribed according to this scheme. After the experiment, the lungs were excised and examined histologically.
Measurements and results: Parenchymal opacification occurred mainly in the dorsal lung areas. The time from the beginning of ventilation to the appearance of lung damage was 60-120 min in the supine (S) group, and 60-270 min in the prone (P) group, and it was significantly longer in the prone group (P < 0.01). We observed diffuse lung damage, including hyaline membrane formation, intra-alveolar edema, and infiltration of inflammatory cells.
Conclusions: Body position affected the time course of the development of VILI, but it did not affect the location.