Prone positioning for patients intubated for severe acute respiratory distress syndrome (ARDS) secondary to COVID-19: a retrospective observational cohort study.

British Journal of Anaesthesia 2021 Jan; 126(1): 48–55. doi: 10.1016/j.bja.2020.09.042

Weiss TT, Cerda F, Brady Scott J et al.


  • COVID-19 causes acute respiratory distress syndrome (ARDS) in approx. 20% hospitalized patients.
  • ARDS – High mortality (35%-46%)
  • Prone positioning recommended by Surviving Sepsis Campaign COVID subcommittee
  • Pre-COVID shown to improve Pa02/Fi02 ratio, reduce 28-day mortality
  • Initial proning shown to improve oxygenation in intubated/non-intubated COVID patients
  • Lack of reports on physiological effects of repeat proning and association with mortality and length of hospital

Study Aim

  • ” To investigate the effect of prone positioning for patients with COVID-19 ARDS that required invasive ventilation”

Study Design

  • Single centre retrospective cohort study, Chicago, USA
  • March 18th-31st 2020
  • Inclusion:
    • Adult ICU patients, confirmed COVID (PCR swab), requiring invasive ventilation and prone positioning
  • Exclusion:
    • Pregnancy
    • Intubated and proned outside of hospital
    • Reintubated and proned on their second intubation in hospital
  • Prone positioning protocol: Video + Checklist, MDT lead by resp therapist
  • Proning Criteria:
  • PaO2/FiO2 ratio of <20 with PEEP 10 cm H20
  • FiO2 >0.6
  • Prone maintained for 16hrs
  • Proning terminated when Pa02/Fi02 remained >20 when supine or ECMO or palliative care required.
  • Lung protective ventilation (TV 6ml/kg, Pplateau , High PEEP/Low Fi02 tables)
  • ECMO considered if lung protective ventilation could not be maintained with proning, paralysis, inhaled pulmonary dilators.


  • Data collected from notes and ABG results for first 3 proning sessions
  • Subject demographics laboratory results and co-morbidities collected
  • Pre and post prone parameters collected:
    • ABG
    • Ventilator settings
    • Pplateau
    • Ventilatory ratio (MVxPaCO2/IBWx100x37.5)
      • Correlates with VD/VT (pulmonary dead space fraction) an independent predictor of mortality in ARDS: higher related to worse outcomes
    • Outcomes collected; each patient followed up until hospital discharge


  • Primary:
    • Oxygenation, assessed by Pa02/Fi02 ratio, before and after initial prone
    • Positive response defined as increase in Pa02/Fi02 ratio 20%
  • Secondary:
    • Serial Pa02/Fi02 ratio after repeated proning – compared between subjects discharged vs required ECMO or died
    • Haemodynamic and Ventilatory parameters on repeat proning


  • 50 subjects, 8 excluded, 42 eligible
  • 25 subjects required proning on at least 3 occasions
  • Total of 31/42 (76%) survived to discharge, avg 21.5-day ICU admission
  • 5 – ECMO, 11- Died
  • Primary outcome:
    • Pa02/Fi02 ratio improved from 17.9 to 28.2 within 81 mins for 36 subjects (P<0.01)
    • Pa02/Fi02 ratio improved 20% in 72% (26/36) subjects
    • Improvements persisted on returning to supine
  • Secondary outcomes:
    • Subjects who were discharged from hospital were more likely to have an improvement in Pa02/Fi02 ratio 20% on second and third proning session, compared to those who died or required ECMO.
    • Ventilatory parameter and CV parameters remained relatively static on prone positioning


  • In this study P/F ratio improvement >20% after first proning showed no differences between treatment success and failure group
  • Did show survivors responded to second and third proning in contrast to little or no response in those who died or needed EMCO
  • 28-day ICU mortality 21.4% (similar to PROSEVA trail)
  • May help in decision making RE: ECMO
  • In subjects who responded to proning, no difference in compliance compared to treatment failure group


  • Small, single centre study
  • Retrospective – non RCT (difficult in pandemic)
  • No CT imaging to assess lung parenchyma for those who didn’t respond to proning
  • Ventilatory ratio used as a surrogate assessment of dead space
  • Absence of some ABG results (put down to immediate need for prone positioning and increased staff workload) leading to 36 of 42 included patients being analysed.
    • Could this introduce bias? Immediacy of proning need linked to acuity of patient?

Study Conclusions

  • Patients with COVID ARDS frequently responded to initial proning with improved oxygenation
  • Subsequent proning in subject who survived to discharge was associated with greater improvements in oxygenation
  • May guide decision making RE: escalation to ECMO
  • Supports practice of prone positioning in COVID ARDS

Summary by Dr C Cregg. Journal Club Meeting 11 March 2021.

(Photo: Marco Mantovani/Getty Images)

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