Introduction Despite advances in critical care technology and in- creased knowledge about the syndrome, mortality in acute respiratory distress syndrome ARDS) remains high. One of the reasons for high mortality is thought to be additional damage induced by mechanical ventila- tion itself [1, 2]. Even though measures are taken to pro- tect the lungs when ventilating ARDS patients, mortali- ty remains high [3]. Placing the patient in a prone posi- tion has been proposed as a relatively simple maneuver to improve oxygenation [4]. Experimental animal stud- ies have suggested that the prone position causes less lung injury than the supine position owing to positive pressure ventilation [5]. In ARDS, the most severe form of acute lung injury ALI), reports state that prone M.Nishimura O.Honda N.Tomiyama T.Johkoh K.Kagawa T.Nishida Body position does not influence the location of ventilator-induced lung injury Received: 3 January 2000 Final revision received: 1 August 2000 Accepted: 3 August 2000 Published online: 14 October 2000  Springer-Verlag 2000 M. Nishimura  ) ) Intensive Care Unit, Osaka University Hospital, 2-15 Yamadaoka, Suita, Osaka 565±0871, Japan E-mail: masaji@hp-icu.med.osaka-u.ac.jp Phone: +81-6-68 79 58 11 Fax: +81-6-68 79 58 23 O. Honda ´ N. Tomiyama ´ T. Johkoh Department of Radiology, Osaka University Medical School, 1-1 Yamadaoka, Suita, Osaka 565-0871, Japan K. Kagawa Department of Anesthesiology, National Cardiovascular Center, 5-7-1 Fujishiro-dai, Suita City, Osaka 565-0873, Japan T.Nishida Department of Anesthesia, Nakatsu-Saiseikai Hospital, 2-10-39 Shibata, Kita-ku, Osaka 530-0012, Japan Abstract Objective: To ascertain whether the locations of ventilator- induced lung injury VILI) are in- fluenced by body position. Design: Randomized prospective short-term study. Setting: Animal laboratory at a uni- versity 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 de- termine the ventilator settings at which the lungs of rabbits were in- jured within 5 h in the supine posi- tion, the ventilator was set at F I O 2 0.21, at a rate of 30/min, T I 0.6 s, peak inspiratory pressure 30 cm H 2 O, 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 posi- tion. Respiratory gases were mea- sured and CT scanning was per- formed every 30 min. The animals were ventilated for 5 h or until pul- monary parenchymal opacification was detected. The lungs were divid- ed into three areas from apex to base and three levels from ventral to dorsal, and the location of opacifi- cation was ascribed according to this scheme. After the experiment, the lungs were excised and examined histologically. Measurements and results: Paren- chymal opacification occurred mainly in the dorsal lung areas. The time from the beginning of ventila- tion to the appearance of lung dam- age 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 forma- tion, intra-alveolar edema, and infil- tration of inflammatory cells. Conclusions: Body position affected the time course of the development of VILI, but it did not affect the lo- cation. Key words Mechanical ventilation ´ Lung injury ´ Body position Intensive Care Med 2000) 26: 1664±1669 DOI 10.1007/s001340000664 EXPERIMENTAL