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

Intensive Care Med. 2020 Dec;46(12):2187-2196. doi: 10.1007/s00134-020-06281-2. Epub 2020 Oct 21.

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 PaO2/FiO2 or for compliance of the respiratory system. Gas exchange, hemodynamics and respiratory mechanics were recorded at 5 and 15 cmH2O PEEP. CT scan variables were measured at 5 cmH2O PEEP.

Results: Anthropometric characteristics were similar in COVID-19-ARDS, PaO2/FiO2-matched-ARDS and Compliance-matched-ARDS. The PaO2/FiO2-matched-ARDS and COVID-19-ARDS populations (both with PaO2/FiO2 106 ± 59 mmHg) had different respiratory system compliances (Crs) (39 ± 11 vs 49.9 ± 15.4 ml/cmH2O, p = 0.03). The Compliance-matched-ARDS and COVID-19-ARDS had similar Crs (50.1 ± 15.7 and 49.9 ± 15.4 ml/cmH2O, respectively) but significantly lower PaO2/FiO2 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/FiO2-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/FiO2-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 cmH2O improved oxygenation in all groups. However, while lung mechanics and dead space improved in PaO2/FiO2-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/FiO2, at least when considered within the timeframe of our study.

Keywords: ARDS; COVID-19; CT scan; Mechanical ventilation; Respiratory system mechanics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Blood Gas Analysis / methods
  • COVID-19 / physiopathology*
  • COVID-19 / therapy
  • Cohort Studies
  • Female
  • Humans
  • Intensive Care Units / organization & administration
  • Intensive Care Units / statistics & numerical data
  • Italy
  • Length of Stay / statistics & numerical data
  • Lung Compliance / physiology
  • Male
  • Middle Aged
  • Prospective Studies
  • Pulmonary Gas Exchange / physiology
  • Respiratory Distress Syndrome / physiopathology*
  • Respiratory Distress Syndrome / therapy
  • Simplified Acute Physiology Score
  • Tomography, X-Ray Computed / methods