Improving Oxygenation in ARDS

OVERVIEW

Refractory hypoxia, leading to dysoxia at the cellular level, can be difficult to manage in severe acute respiratory distress syndrome (ARDS)

  • protective lung ventilation strategies should be used (e.g. ARDSNet protocol) to prevent worsening from ventilator-induced lung injury (VILI)
  • many of the strategies commonly used lack a strong evidence base
  • these strategies may help improve oxygenation in selected lung conditions other than ARDS, where there is a strong rationale

APPROACH

Basic measures

  • increase FiO2 to improve PAO2
  • increased PEEP
    • increase surface area for gas exchange
    • decrease atelectasis
    • redistribution of lung water

General measures

  • physio and suctioning
  • sedation and paralysis
    • decreased O2 consumption and CO2 production
    • the ACURASYS trial found a mortality benefit with early atracurium neuromuscular blockade
  • treat factors that increase metabolic demand; e.g. sepsis
  • optimise fluid balance
    • maximise cardiac output and oxygen delivery
    • minimise interstitial overload
  • optimise Hb
    • optimal oxygen carriage and minimise immune and volume effects of transfusion
  • diuretics
  • albumin
    • a small trial supports the use of concentrated albumin with frusemide in hypoproteinaemic ARDS patients

Optimise recruitment and FRC

  • lung recruitment manoeuvre
    • open collapsed alveoli, increased FRC and area available for gas exchange
    • uncertain benefit; increased mortality in the ART trial
  • increased I:E ratio towards 1:1 (from 1:1.5 to 1:2 which is a typical standard ratio)
    • increases FRC, recruitment and PAO2
  • inverse ratio ventilation
    • longer time in inspiration with potential gas trapping
    • provides autoPEEP above set PEEP with subsequent increase in FRC and area for gas exchange
  • consider airway pressure release ventilation (APRV)
    • unproven
  • prone positioning
    • better V/Q, improved mechanical advantage, less lung compression from abdominal and mediastinal contents
    • improved mortality in severe ARDS in meta-analyses and PROSEVA trial

Optimise Flow to Ventilated Alveoli

  • inhaled NO
    • dilator delivered only to ventilated alveoli (evidence lacking)
  • prostacyclin
    — mproved perfusion to ventilated alveoli (evidence lacking)

Last Resorts

  • tracheal gas insufflation
    — decrease circuit dead space providing lower CO2 with relative increase in PAO2
  • High-frequency oscillation ventilation (HFOV)
    • no benefit in large RCTs (OSCAR and OSCILATE)
  • VEno-venous extracorporeal membrane oxygenation (VV ECMO)
    •  improved oxygenation + lung rest and minimisation of ventilator associated lung injury
    • supported by CESAR trial

References and Links

Journal articles

  • Collins SR, Blank RS. Approaches to refractory hypoxemia in acute respiratory distress syndrome: current understanding, evidence, and debate. Respiratory care. 56(10):1573-82. 2011. [pubmed]
  • Cortés I, Peñuelas O, Esteban A. Acute respiratory distress syndrome: evaluation and management. Minerva Anestesiol. 2012 Mar;78(3):343-57. [pubmed] [Free Full Text]

FOAM and web resources


CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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