Does proning work for patients with COVID-19 induced ARDS?

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

Weiss et al. 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, S0007-0912(20)30837-0.

Take Home Message

Whilst this is a small-scale trial over a short period of time, it shows that there is a significant improvement in the oxygenation, based on the Pa02/Fi02 (P/F) ratio, after proning patients with severe ARDS due to Covid 19, with little change in the haemodynamic stability.

Background

Studies show that proning can be improve oxygenation in ARDS patients, however this has not been investigated in ARDS secondary to Covid-19. It is known that ARDS can present in 20% of Covid-19 patients and this has a high mortality rate (35-45%), therefore evidenced based management is important to utilise in these patients.

Aim

The aim of this study was to investigate the effect of prone positioning for patients with COVID-19 ARDS that required invasive mechanical ventilation.

Design

  • Retrospective single-centre observational cohort study based in Chicago, USA.
  • Data collected between 18th March 2020 and 31st March 2020.
  • Inclusion criteria: Adults admitted to ICU with COVID-19 infection requiring invasive mechanical ventilation with prone positioning.
  • Exclusion criteria: pregnant, intubated and proned at an outside hospital and reintubated and proned on their second intubation.

  • Proning criteria : P/F ratio of <20 kPa with PEEP >=10 cmH2O and >=FiO2 0.6.
  • Patients were proned for 16 hours except if CPR was needed.
  • Terminated when PaO2/FiO2 ratio remained >20kPa in the supine position, ECMO or a decision for palliation.
  • Lung protective ventilation was used.

Methodology

  • Data collected from ICU notes and calculated from ABG results (P/F ratio).
  • Data collected on demographics, pre-existing illness and pre and post proning changes in oxygenation, haemodynamics, ventilator settings and lab tests. 
  • A positive response was defined as an increase in PaO2/FiO2 ratio of 20%.

Outcomes

The primary outcome was oxygenation, assessed by P/F ratio, before and after the initial prone positioning manoeuvre.

The secondary outcomes were: the assessment of serial P/F ratios after repeated prone positioning and comparing this with patient outcome and haemodynamic and ventilatory parameters after repeated prone positioning.

Results

  • 42 participants recruited, 31 of whom survived to discharge.
  • The mean P/F ratio improved from 17.9 to 28.2 kPa within 81 minutes of prone positioning in 36 subjects (P<0.01).
  • The P/F ratio improved by 20% in 26/36 (72%) patients.
  • The second and third proning sessions showed that the improvement was significantly  higher in the treatment success group than in the failure group.
  • Secondary outcomes: ventilatory ratio and rate both increased post-proning and haemodynamic variables remained constant

Study Limitations

  • Very small study – only 42 patients.
  • Single centre study.
  • Retrospective data.
  • Only 36 patients analysed in results as seven patients had incomplete ABG data . This was a potential source of bias as these patients may have been sicker and therefore proned before there was time to take an ABG.
  • No CT scans done on patients to assess lung state pre or post proning.
  • The P/F ratio was used to quantify oxygenation and measure the success of proning, although it is not always associated with better outcomes. In the ARDSnet trial P/F ratios were better in these with much larger lung volumes but outcome was worse.
  • Ventilatory ratio was used as a surrogate assessment of dead space.
  • Patients were on different medications for treatment of Covid-19, this could have been a confounding factor, although there is no significant difference between treatment success and failure groups.
  • Data not available about mortality between the treatment success and failure groups.

Discussion

  • Positive points: difficult to conduct a large RCT during a pandemic and this small study allows us to continue practice with an evidence base.
  • The study looked at a physiological outcome rather than an actual patient improvement or mortality rate.
  • Overall oxygenation improved after proning (P/F ratio) and this was associated with better outcomes.
  • 28 day ICU mortality 21.4% similar to PROSEVA Trial.
  • All patients PF ratios improved after first prone. Survivors improved in 2nd and 3rd, but treatment failure group did not. (req ECMO)
  • Ventilatory ratio increased post prone, this could be due to alveolar over distension as same PEEP used as pre-prone.
  • Based on this data we should continue proning patients that need it as this study provides an evidence base for this practice in covid-19 paitents with ARDS.

Summary by Dr Shivani J Pandya

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