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.

 Background

• 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 18^th-31^st 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.

Methods

• 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

Outcomes

• 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

Results

• 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

Discussion

• 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

Limitations

• 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)