Sustained Oxygenation Improvement After First Prone Positioning Is Associated with Liberation from Mechanical Ventilation and Survival in Critically Ill COVID-19 Patients: A Cohort Study

Background: Prone positioning (PP) has been used to improve oxygenation in patients affected by the SARS-CoV-2 disease (COVID-19). Several mechanisms, including lung recruitment and better lung ventilation/perfusion matching, make a relevant rationale for using PP. However, not all patients maintain the oxygenation improvement after returning to supine position. Nevertheless, no evidence exists that a sustained oxygenation response after PP is associated to outcome in mechanically ventilated COVID-19 patients. Methods: We analyzed data from 191 patients affected by COVID-19 related acute respiratory distress syndrome undergoing PP for clinical reasons. Clinical history, severity scores and respiratory mechanics were analyzed. Patients were classified as responders (≥50% PaO2/FiO2 increase) or non-responders (<50% PaO2/FiO2 increase) based on the PaO2/FiO2 increase after returning to supine position from the first PP session. Differences among the groups in physiological variables, complication rates and outcome were evaluated. A competing risk regression analysis was conducted to evaluate if PaO2/FiO2 response after the first pronation cycle was associated to liberation from mechanical ventilation. Findings: No differences in demographics, comorbidities, ventilatory treatment and PaO2/FiO2 before PP were found between responders (91/191) and non-responders (98/191). Despite no differences in ICU length of stay, non-responders had a higher rate of tracheostomy (49·5 vs 68·4%, P=0·008) and mortality (53·1% vs 33·3%, p=0·006), as compared to responders. Moreover, oxygenation response after the first PP was independently associated to liberation from mechanical ventilation at 28 days. Interpretation: Sustained oxygenation improvement after first PP session is independently associated to improved survival and reduced duration of mechanical ventilation in critically ill COVID-19 patients. Trial Registration: The study was registered in ClinicalTrials.gov (NCT04411459). Funding Statement: None. Declaration of Interests: None. Ethics Approval Statement: The study was approved by the Institutional Review Board of the study coordinator center (Maggiore Hospital, Bologna, Italy, approval number: 273/2020/OSS/AUSLBO) and by each institutional review committee of the participating hospitals. Informed consent was partially waived according to the approval of the local Ethics committee and analysis was conducted on anonymized individual data.