Supplementary Material for: The effect of positive pressure ventilation on Acute Kidney Injury in COVID-19 patients with Acute Respiratory Distress Syndrome. An observational study.

Introduction: Acute kidney injury (AKI) is frequent in critically ill COVID-19 patients and is associated with a higher mortality risk. By increasing intrathoracic pressure, positive pressure ventilation (PPV) may reduce renal perfusion pressure by reducing venous return to the heart or by increasing renal venous congestion. This study’s aim was to evaluate the association between AKI and hemodynamic and ventilatory parameters in COVID-19 patients with ARDS. Methods: this is a single-centre retrospective observational study. Consecutive patients diagnosed with COVID-19 who met ARDS criteria and required invasive mechanical ventilation were enrolled. The relationship between respiratory and hemodynamic parameters influenced by positive pressure ventilation and AKI development was evaluated. AKI was defined according to KDIGO criteria. AKI recovery was evaluated a month after ICU admission and patients were classified as “recovered”, if serum creatinine (sCr) value returned to baseline, or as having “acute kidney disease” (AKD), if criteria for AKI stage 1 or greater persisted. The 6-month all-cause mortality was collected. Results: 144 patients were included in the analysis. AKI occurred in 69 (48%) patients and 26 (18%) required Renal Replacement Therapy (RRT). In a multivariate logistic regression analysis, sex, hypertension, cumulative dose of furosemide, fluid balance, and plateau pressure were independently associated with AKI. Mortality at 6 months was 50% in the AKI group and 32% in the non-AKI group (p=0.03). Among 36 patients who developed AKI and were discharged alive from the hospital, 56% had a full renal recovery after a month, while 14%, 6% and 14% were classified as having an Acute Kidney Disease (AKD) of stage 0, 2 and 3, respectively. Conclusions: in our cohort, AKI was independently associated with multiple variables, including high plateau pressure, suggesting a possible role of positive pressure ventilation on AKI development. Further studies are needed to clarify the role of mechanical ventilation on renal function.