Sustained oxygenation improvement after first prone positioning is associated with liberation from mechanical ventilation and mortality in critically ill COVID-19 patients: a cohort study

Abstract

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 rational 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. 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 (≥ median PaO₂/FiO₂ variation) or non-responders (< median PaO₂/FiO₂ variation) based on the PaO₂/FiO₂ percentage change between pre-proning and 1 to 3 h after re-supination in the first prone positioning 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.

Results: The median PaO₂/FiO₂ variation after the first PP cycle was 49 [19-100%] and no differences were found in demographics, comorbidities, ventilatory treatment and PaO₂/FiO₂ before PP between responders (96/191) and non-responders (95/191). Despite no differences in ICU length of stay, non-responders had a higher rate of tracheostomy (70.5% vs 47.9, P = 0.008) and mortality (53.7% 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 and was increasingly higher being higher the oxygenation response to PP.

Conclusions: 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.

Keywords: COVID19; ICU; Prone positioning; Ventilatory free days.

Fig. 1

Physiologic effect of the first prone positioning session and impact on patient outcome. Effect of the first proning session on change in PaO₂/FiO₂ ratio (a PaO₂/FiO₂ in after prone position minus PaO₂/FiO₂ before prone position), change in driving pressure (b driving pressure after prone position minus driving pressure before prone position) and ventilator-free days (c) in responders (blue) and non-responders (grey) patients with acute respiratory distress syndrome related to COVID-19

Fig. 2

Cumulative incidence of liberation from mechanical ventilation. Cumulative incidence of liberation from mechanical ventilation (MV) over 28 days after intubation. The four curves represent the cumulative incidence functions related to the quartiles of PaO₂/FiO₂ response to prone positioning referred to the multivariate model (Table 3)