Respiratory physiology of COVID-19 and Influenza associated Acute Respiratory Distress Syndrome

Abstract

Background: There is ongoing debate whether lung physiology of COVID-19 associated acute respiratory distress syndrome (ARDS) differs from ARDS of other origin.Objective: The aim of this study was to analyze and compare how critically ill patients with COVID-19 and Influenza A or B were ventilated in our tertiary care center with or without extracorporeal membrane oxygenation (ECMO). We ask if acute lung failure due to COVID-19 requires different intensive care management compared to conventional ARDS. Methods: 25 patients with COVID-19 associated ARDS were matched to a cohort of 25 Influenza patients treated in our center from 2011 to 2021. Subgroup analysis addressed whether patients on ECMO received different mechanical ventilation than patients without extracorporeal support.Results: Compared to Influenza-associated ARDS, COVID-19 patients had higher ventilatory system compliance (40.7 ml/mbar [31.8 – 46.7 ml/mbar] vs. 31.4 ml/mbar [13.7 – 42.8 ml/mbar], p = 0.198), higher ventilatory ratio (1.57 [1.31 – 1.84] vs. 0.91 [0.44 – 1.38], p = 0.006) and higher minute ventilation at the time of intubation (mean minute ventilation 10.7 l/min [7.2 – 12.2 l/min] for COVID-19 vs. 6.0 l/min [2.5 – 10.1 l/min] for Influenza, p = 0.013). There were no measurable differences in P/F ratio, positive end-expiratory pressure (PEEP) and driving pressures (ΔP). Respiratory system compliance deteriorated considerably in COVID-19 patients on ECMO during 2 weeks of mechanical ventilation (Crs, mean decrease over 2 weeks -23.87 ml/mbar ± 32.94 ml/mbar, p = 0.037), but not in ventilated Influenza patients on ECMO and less so in ventilated COVID-19 patients without ECMO. For COVID-19 patients, low driving pressures on ECMO were strongly correlated to a decline in compliance after 2 weeks (Pearson’s R 0.80, p = 0.058). Overall mortality was insignificantly lower for COVID-19 patients compared to Influenza patients (40% vs. 48%, p = 0.31). Outcome was insignificantly worse for patients requiring veno-venous ECMO in both groups (50% mortality for COVID-19 on ECMO vs. 27% without ECMO, p = 0.30 / 56% vs 34% mortality for Influenza A/B with and without ECMO, p = 0.31)Conclusion: The pathophysiology of early COVID-19-associated ARDS differs from Influenza-associated acute lung failure by sustained respiratory mechanics during the early phase of ventilation. We question whether intubated COVID-19 patients on ECMO benefit from extremely low driving pressures, as this appears to accelerate derecruitment and consecutive loss of ventilatory system compliance.