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Evaluation of time constant, dead space and compliance to determine PEEP in COVID-19 ARDS: a prospective observational study

  • Filip Depta1,2,*,
  • Michael A. Gentile3
  • Richard H. Kallet4,5
  • Viliam Donic6
  • Marko Zdravkovic7,8

1Department of Critical Care, East Slovak Institute for Cardiovascular Diseases, 04011 Košice, Slovakia

2Faculty of Medicine, Pavol Jozef Šafárik University, 04011 Košice, Slovakia

3Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA

4Department of Anesthesia, University of California, San Francisco, CA 94110, USA

5San Francisco General Hospital, San Francisco, CA 94110, USA

6Department of Physiology, Pavol Jozef Šafárik University, 04011 Košice, Slovakia

7Department of Anaesthesiology, Intensive Care and Pain Management, University Medical Centre Maribor, 2000 Maribor, Slovenia

8Faculty of Medicine, University of Ljubljana, 1000 Ljubljana, Slovenia

DOI: 10.22514/sv.2023.026

Submitted: 01 February 2023 Accepted: 14 March 2023

Online publish date: 26 April 2023

*Corresponding Author(s): Filip Depta E-mail:


Multiple variables exist to identify optimal positive end-expiratory pressure (PEEP) to keep alveolar recruitment in acute respiratory distress syndrome (ARDS). These include increased respiratory system compliance (CRS ) and decreased dead space to tidal volume fraction (Vd/Vt). Increasing CRS reflects improved lung volume, whereas decreasing Vd/Vt reflects improved ventilation/perfusion matching. An increasing expiratory time constant (RCEXP ) reflects both, changes in CRS and alterations in tissue resistance. Whether RCEXP might reflect corresponding changes in Vd/Vt better than CRS during alveolar recruitment is unknown. This prospective observational study examined the correlation between these variables during ascending PEEP titration in patients with novel Coronavirus disease (COVID-19) related ARDS. PEEP titrations were performed in ten patients with COVID-19 ARDS under passive, pressure-controlled ventilation with a fixed driving pressure of 14 cmH2O. PEEP was increased stepwise between 5 and 20 cmH2O with 2 minutes allowed for Vd/Vt equilibration. RCEXP , Vd/Vt and CRS were recorded at each PEEP level and statistically assessed.The overall correlation between Vd/Vt and RCEXP was −0.72 (95% CI: −0.57 to −0.82); p < 0.0001. CRS had a weaker correlation with Vd/Vt (−0.47 (95% CI: −0.25 to −0.64); p < 0.0001). RCEXP was the highest at 12 cmH2O of PEEP whereas Vd/Vt was the lowest at 10 cmH2O of PEEP and CRS was the highest at PEEP of 15 cmH2O.Both parameters of exhalation, Vd/Vt and RCEXP, are strongly correlated which likely reflects corresponding mechanical and global ventilation/perfusion responses during ascending PEEP titration.


Acute respiratory distress syndrome; COVID-19; Positive end-expiratory pressure; Expiratory time constant; Lung perfusion; Dead space ventilation

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Filip Depta,Michael A. Gentile,Richard H. Kallet,Viliam Donic,Marko Zdravkovic. Evaluation of time constant, dead space and compliance to determine PEEP in COVID-19 ARDS: a prospective observational study. Signa Vitae. 2023.doi:10.22514/sv.2023.026.


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