Physiological and quantitative CT-scan characterization of COVID-19 and typical ARDS: a matched cohort study
Davide Chiumello, Mattia Busana, Silvia Coppola, Federica Romitti, Paolo Formenti, Matteo Bonifazi, Tommaso Pozzi, Maria Michela Palumbo, Massimo Cressoni, Peter Herrmann, Konrad Meissner, Michael Quintel, Luigi Camporota, John J. Marini, Luciano Gattinoni
Abstract
To investigate whether COVID-19-ARDS differs from all-cause ARDS. Thirty-two consecutive, mechanically ventilated COVID-19-ARDS patients were compared to two historical ARDS sub-populations 1:1 matched for PaO 2 /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. Anthropometric characteristics were similar in COVID-19-ARDS, PaO 2 /FiO 2 -matched-ARDS and Compliance-matched-ARDS. The PaO 2 /FiO 2 -matched-ARDS and COVID-19-ARDS populations (both with PaO 2 /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 PaO 2 /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 (PaO 2 /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 PaO 2 /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 PaO 2 /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. COVID-19-ARDS is a subset of ARDS characterized overall by higher compliance and lung gas volume for a given PaO 2 /FiO 2 , at least when considered within the timeframe of our study.