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

Abstract

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 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. Results: 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. Conclusions: 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.

An Appraisal of Respiratory System Compliance In Mechanically Ventilated Covid-19 Patients

“…In addition, they found that patients who presented with lower C RS and higher D-dimer values had the greatest mortality risk. In line with these gures, in a small-case series Chiumello and collaborators found that COVID-19 patients presented higher C RS levels in comparison with patients with ARDS from other etiologies and matched levels of hypoxemia [12]. Regrettably, those previous reports did not provide any information on how C RS progressed beyond a punctual assessment during the period of MV.…”

“…Female sex presented lower C RS than in males (95% CI: -13.8 to -8.5 P < 0.001) and higher body mass index (34.7 ± 10.9 vs 29.1 ± 6.0, p < 0.001). Median (IQR) PEEP was 12 cmH 2 O (10)(11)(12)(13)(14)(15), throughout the range of C RS , while median (IQR) driving pressure was 12.3 (10)(11)(12)(13)(14)(15) cmH 2 O and signi cantly decreased as C RS improved (p < 0.001). No differences were found in comorbidities and clinical management between C RS strata.…”

“…Earlier reports on the pulmonary pathophysiology of COVID-19 patients reported con icting results and extreme heterogeneity in levels of pulmonary shunting, static respiratory system compliance (C RS ), [9][10][11][12] and substantial heterogeneity in lung recruitability [13,14]. Adding further to the controversy over C RS in recently,Grasselli and collaborators [7] have compared ndings from an Italian repository of COVID-19 ARDS vs. previous ARDS cases of different etiologies.…”

COVID-19 and ARDS: the baby lung size matters

“…We read with interest the editorial by Goligher, Ranieri and Slutsky [1] as it provides an excellent summary of the results of our study on the characteristics of coronavirus disease 2019 (COVID-19) related acute respiratory distress syndrome (ARDS) [2]. The editorialists recognize that our population of patients with severe COVID-19 exhibited anatomical and physiological characteristics that are distinct from the two matched cohorts of typical ARDS.…”

Is severe COVID-19 pneumonia a typical or atypical form of ARDS? And does it matter?

“…In a recent article, Chiumello et al approach these questions by comparing the respiratory pathophysiological features of patients with early COVID-19 ARDS to historical controls with classical (non-COVID-19) ARDS [1]. A hallmark of classical ARDS is that hypoxemia results predominantly from atelectasis and consolidation, with a consequent increase in physiological shunt fraction [2,3].…”