Abstract Background Studies have demonstrated that over 20% of patients with moderate to severe acute respiratory distress syndrome (ARDS) do not exhibit significant improvement in oxygenation following prone positioning ventilation (PPV). The underlying physiological mechanisms in patients unresponsive to PPV remained to be elucidated. The aim of this study was to investigate the physiological effects of PPV by using electrical impedance tomography (EIT), and to explore the predictors of response to PPV in patients with moderate to severe ARDS during the early phase. Methods This is a single-center, prospective, observational study. Ninety-four adult patients who were diagnosed with moderate-to-severe ARDS according to the Berlin definition (PaO2/FiO2150mmHg) and underwent protocolized PPV within 48 hours post-intubation were enrolled. EIT data and clinical variables were collected at two time points: before PPV (in the supine position) and 16 hours after PPV (PPV16h, in the prone position). EIT data were analyzed for the global, separated ventral/dorsal regions, and separated four gravity-dependent regions of interest (ROI1-4). Results Of the 94 enrolled patients, 78 (83%) were defined as PPV responders and 16 (17%) were nonresponders. Compared to the nonresponders, the respiratory system compliance (Crs) in responders was significantly higher (35.6±7.5 cmH2O/mL vs. 31.4±5.8 cmH2O/mL, p=0.037) before PPV. The center of ventilation (COV) index was higher in responders compared with nonresponders (median Interquartile range 45.1 41.7-48.1 vs. 40.5 38.0-45.7, p = 0.035) before PPV. Compared to the responders, the V/Q mismatch% in ROI3 was higher in the nonresponders (20.8% 16.4-24.6 vs 13.0% 8.7-18.2, p=0.002) before PPV. The shunt% in ROI3 was also higher in the nonresponders (14.3% 10.4-19.6 vs 4.9% 1.6-8.5, p0.001) before PPV. The multivariate logistic regression analysis showed that shunt% in ROI3 before PPV was an independent predictor of response to PPV (OR 1.190, 95% CI 1.055-1.342, p = 0.005). The receiver operating characteristic (ROC) curve analysis indicated that shunt% in ROI3 before PPV predicted response to PPV with an AUC of 0.89 (95% CI 0.82-0.95, p0.001). The cut-off value of the shunt% in ROI3 before PPV was 8.4%, which predicted the response to PPV with 94% sensitivity and 76% specificity. Conclusion For moderate to severe ARDS patients, the shunt% at ROI3 before PPV could help to predict the response of PPV during the early phase. This abstract is funded by: None
Shang et al. (Fri,) studied this question.