ARDS 3×3

A session blog from Day 2 of State of the Art, London December 2015. See the full list

Blogger Jack Wong

Chair: John Kheir & Anthone Vieillard Baron

 

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From left to right – Fan, Gattinoni, MacSweeney

Stretching the lung is not harmful

Gattinoni (pro) vs. Mac Sweeney(con)

Summary/Key messages

Gattinoni

  • “VILI does not exist!”

 

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  • Physiologically speaking, as inferred from animal model, we can endure large lung volume without significantly harmful rise in lung pressure.
  • The concept of continuous strain with high PEEP ventilation would equate no energy input hence little harm is incurred (ie you need energy to cause stress and strain)
  • Lung injury is not determined by single factor such as pressure / volume / flow etc but rather a composite of energy caused but when it is managed in the lower threshold it is relatively safe.

MacSweeney

  • Quoting the history of the “Charge of the Light Brigade”, Rob quotes a handful of evidences which show protective lung ventilation strategy is preferred as compared to ventilation with larger tidal volume – Hinting that the idea of “VILI (VALI) doesn’t exist” by Gattinoni is akin to Lord Cardigan leading the crowd charging into “the VALI of death”

 

ECMO: You’re doing it wrong

Gattinoni (pro) vs. Fan (con)

Summary/Key messages

Gattinoni

  • The lung rest concept using extracorpeal membrane lung was introduced by Kolobow in 1977 but is associated with high rate of complications such as blood loss and technical issues.
  • However, while patient is on ECMO, the intended low volume ventilation (protective ventilation strategy) allows alveoli collapse which worsened patients’ condition due to atelectasis.
  • The alveoli should instead be “stretched” to maintain opened alveoli.
  • Therefore, it seems counter-intuitive to use low volume ventilation in ARDS (to allow atelectasis) instead of promoting some degree of “pressure” in the lung.
  • Problems arise when lung pressure (Pl) is low
    • Insufficient total ventilation
    • pCO2 rise
    • Atelectasis
    • Worsening hypoxemia
    • Increased pulmonary hypertension
    • RV faliure.
  • Hence, keep the lung “inflated” when ECMO is in use.

Fan

  • Well documented uncertainty regarding what lung pressure / MV should be maintained at when ECMO was introduced.
  • However, mortality data on various trials shows low volume is preferred – concept of “baby lung”:
    • ARDSnet NEJM 2000 – 6ml/kg vs 12ml/kg (31.0% vs 39.8%)
    • Needham BMJ 2012 – 6 ml has better 2 year mortality
    • Terragni PP Anaesthesiology 2009 – TV lower than 6 ml / kg enhances lung protection
    • Bein T Intensive Care Medicine 2013 – Xtravent-study =
    • Pham T Am J Respir Crit Care Med 2013 – ECMO for Pandemic H1N1
  • Various strategies to achieve “lung rest” have been described but effect of clinical outcomes is limited. Hence, more data is required – work in progress:

ARDS definition is killing advances in the field

MacSweeney (pro) vs. Fan (con)

Summary/Key messages

MacSweeney

  • Comparing the rise and fall of Hindenburg to the introduction and limitation of ARDS definition – MacSweeney is setting a rather impressive presentation style!
  • ARDS is described by Rene Laennec nearly two centuries ago, followed by recent definition attemps
  • Current definition only correlates to 50% of actual pathology of ARDS – it is a flawed criteria and poor definition.
  • Could this relate to the results in hundreds on negative trial?
  • Perhaps we should be looking at tissue biomarker rather than syndrome definition and there is a need to move forward unto “post ARDS era

Fan

    • Syndromes are commonly described in critical care medicine.
    • Benefits of defining ARDS:
      • Enable epidemiological studies
      • Facilitate enrolment into clinical trials
      • Allow comparison between studies
      • Enhance linkage with basic science
      • Ability to implement results of positive RCTs in clinical practise
      • May be useful in prognostic discussion with patients and families
      • Useful in planning resource allocation
    • AECC definition
      • CXR unreliable
      • Poor inter-observer agreement on PAOP
      • P/F ratio is treatment dependent
      • Left atrium hypertension often co exists with ALI

 

  • Berlin definition

 

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  • Limitation and concerns
  • Berlin classification does not standardize mechanical ventilation at the time of oxygenation assessment
  • Oxygenation after 24 hours of standardized MV clearly associated with mortality better than baseline oxygenation
  • Many variables and measures of interest were not included (eg EVLW, biomarkers, CT, PEEP, compliance, dead space)

 

 

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