Physiological and quantitative CT-scan characterization of COVID-19 and typical ARDS: a matched cohort study

Purpose To investigate whether COVID-19-ARDS differs from all-cause ARDS. Methods Thirty-two consecutive, mechanically ventilated COVID-19-ARDS patients were compared to two historical ARDS sub-populations 1:1 matched for PaO2/FiO(2)or for compliance of the respiratory system. Gas exchange, hemodynamics and respiratory mechanics were recorded at 5 and 15 cmH(2)O PEEP. CT scan variables were measured at 5 cmH(2)O PEEP. Results Anthropometric characteristics were similar in COVID-19-ARDS, PaO2/FiO(2)-matched-ARDS and Compliance-matched-ARDS. The PaO2/FiO(2)-matched-ARDS and COVID-19-ARDS populations (both with PaO2/FiO(2)106 +/- 59 mmHg) had different respiratory system compliances (Crs) (39 +/- 11 vs 49.9 +/- 15.4 ml/cmH(2)O,p = 0.03). The Compliance-matched-ARDS and COVID-19-ARDS had similar Crs (50.1 +/- 15.7 and 49.9 +/- 15.4 ml/cmH(2)O, respectively) but significantly lower PaO2/FiO(2)for the same Crs (160 +/- 62 vs 106.5 +/- 59.6 mmHg,p < 0.001). The three populations had similar lung weights but COVID-19-ARDS had significantly higher lung gas volume (PaO2/FiO(2)-matched-ARDS 930 +/- 644 ml, COVID-19-ARDS 1670 +/- 791 ml and Compliance-matched-ARDS 1301 +/- 627 ml,p < 0.05). The venous admixture was significantly related to the non-aerated tissue in PaO2/FiO(2)-matched-ARDS and Compliance-matched-ARDS (p < 0.001) but unrelated in COVID-19-ARDS (p = 0.75), suggesting that hypoxemia was not only due to the extent of non-aerated tissue. Increasing PEEP from 5 to 15 cmH(2)O improved oxygenation in all groups. However, while lung mechanics and dead space improved in PaO2/FiO(2)-matched-ARDS, suggesting recruitment as primary mechanism, they remained unmodified or worsened in COVID-19-ARDS and Compliance-matched-ARDS, suggesting lower recruitment potential and/or blood flow redistribution. Conclusions COVID-19-ARDS is a subset of ARDS characterized overall by higher compliance and lung gas volume for a given PaO2/FiO(2), at least when considered within the timeframe of our study.