The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

INADEQUATE DURATION IN THE PRONE POSITION RESULTING IN DECREASED OXYGENATION AFTER TURNING BACK TO THE SUPINE POSITION IN AN ANIMAL MODEL WITH ACUTE RESPIRATORY DISTRESS SYNDROME.

Yanling Wang1, Qian Xiao1, Ying Wu1, Jihong Sun2, Yahong Xu1, Hongyuan Tang1, Shulan Li1, Shuqin Xiao1, Ying Deng1, Yisi Liu1, Yan Zhang1; 1School of Nursing, China Capital Medical University, Beijing, China; 2Beijing Chaoyang Hospital, Beijing, China

Background: Despite the belief that the prone position (PP) improves oxygenation in ARDS and ALI, studies on mortality in patients are inconsistent. A meta-analysis showed that, in those studies that resulted in uncertain effects of PP on mortality, the average daily duration of PP was 7-hours. The aim of this study was to investigate oxygenation changes related to PP for 8, 16, and 24 hours over a 24-hour period, in a porcine model of ARDS/ALI. Methods: Fifteen female pigs (30.21 ± 3.24kg, 76.5 ± 5.9cm) were anesthetized and ventilated. Lung injury was induced via intra-tracheal lavage with HCl (pH 1.0) to create an ARDS/ALI model. The pigs were randomly assigned to either: an 8-h group (PP for 8 hours, supine for 16 hours); a 16-h group (PP for 16 hours, supine for 8 hours); and a 24-h group (PP for 24 hours). ABGs and hemodynamics were measured every four hours for 24 hours and the intrapulmonary shunt index (QS/QT) was calculated. Lung wet-to-dry ratio (W/D) and histology were used to examine the trends of oxygenation differences in the groups. Data were examined by ANOVA. Results: After turning to PP, the PaO2/FiO2 levels in all 3 groups increased rapidly. After 8 hours in PP, the PaO2/FiO2 of the 8-h group began to drop and was close to pre-prone levels at 24 hours. No drop in PaO2/FiO2 levels was observed in the other 2 groups. The mean PaO2/FiO2 levels in the16-h group and the 24-h group were significantly higher than in the 8-h group over the 24-hour period (PaO2/FiO2 at baseline, 8, 16, and 24 hours in the 8-h group vs. 16-h group vs. 24-h group respectively: 151.3 ± 34.0, 251.8 ± 65.3, 179.9 ± 113.4, and 170.1 ± 102.4 vs. 146.6 ± 47.3, 264.1 ± 66.2, 285.9 ± 52.2, and 322.6 ± 17.1 vs. 157.0 ± 28.8, 267.2 ± 54.7, 319.8 ± 109.8, and 346.3 ± 49.6, P < 0.05). There was a significant decrease in Qs/QT in the 24-h group compared to the 8-h group (17.7 ± 6.0% vs. 27.7 ± 6.3% at 24 hours, P= 0.035). There were no significant differences in hemodynamics, W/D, and the injury scores. Conclusion: Oxygenation in this porcine model was positively correlated to the duration of PP over a 24-hour period. PP for 8 hours a day did not effectively decrease the intrapulmonary shunt, therefore could not maintain improved oxygenation in the ARDS/ALI porcine model. Lying PP for 16 hours or longer was safer and effectively improved oxygenation by decreasing the intrapulmonary shunt. Sponsored Research - Beijing education and scientific research department
The comparison of PaO2/FiO2 for 3 groups at different time
*P < 0.05, ** P < 0.01