Ventilatorassociated Lung Injury

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Ventilator-associated Lung Injury

• Ri ???

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Complications of Mechanical Ventilator

• Barotrauma
• Nosocomial pneumonia
• Oxygen toxicity
• Hypotension
• Stress ulceration cholestasis

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Barotrauma

• High pressure (i.e., gt 50cmH2O)
• Interstitial emphysema
• Pneumomediastinum
• Subcutaneous emphysema
• pneumothorax

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Nosocomial pneumonia

• Patient intubated longer than 72 hours
• Aspiration from the upper airways through small
  leaks around the tube cuff
• Enteric G(-) rods, S. aureus, anaerobic bacteria

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Oxygen toxicity

• FiO2 gt 60 for more than 72 hours

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Hypotension

• Elevated intrathoracic pressures with decreased
  venous return, intravascular volume repletion

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Gastrointestinal effects

• Stress ulcerations
• H2-receptor antagonists or sulcralfate
• Mild to moderate cholestasis
• T-Bil lt 4.0

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Ventilator-associated Lung Injury (VALI)

• Liap Pinhu, Thomas Whitehead, Timothy Evans, Mark
  Griffiths
• Lancet 2003361332-40 Review

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Ventilator-associated Lung Injury (VALI)

• Definition lung damage caused by application of
  positive or negative pressure to the lung by
  mechanical ventilation.
• oxygen toxicity?

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Mechanisms of VALI1

• Volutrauma damage caused by over-distension.
  High volume or high-end inspiratory volume injury
• Barotrauma high pressure induced lung damage
• Similar histological appearance,
  high-permeability pulmonary edema in uninjured
  lung exacerbated damage in injured lung
• Alveolar over-distention rather than pressure
  itself causes lung injury

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Mechanisms of VALI2

• Atelectotrauma lung injury associated with
  repeated recruitment and collapse, low
  end-expiratory volume injury
• Theoretically prevented by using a level of
  positive end-expiratory pressure (PEEP) greater
  than the lower inflection point of the pressure
  volume curve
• The pressure needed to reopen an occluded airway
  is inversely proportional to its diameter ?
  damage occurs distally

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Protective ventilation strategy

• PEEP set at 2 cmH2O above the lower inflection
  point of the pressure-volume curve
• Driving pressure lt 20cmH2O
• Peak pressure lt 40 cmH2O
• Respiratory Rate lt 30/min

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Conventional v.s. Protective ventilation in
patients with ARDS1

• Spontaneous breathing at rest tidal volume
  about 7mL/kg
• Conventional ventilation
• tidal volume at least 10mL/kg,
• maintain a normal PaCO2

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Conventional v.s. Protective ventilation in
patients with ARDS2

• Protective ventilation
• Low tidal volume 57mL/kg plateau pressure to
  35 cmH2O
• permissive hypercapnia
• a non-randomised study in 1990 a consensus
  conference recommended in 1993

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Conventional v.s. Protective ventilation in
patients with ARDS3
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Multiple organ failure associated with mechanical
ventilation1
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Multiple organ failure associated with mechanical
ventilation2

• Biotrauma pulmonary and systemic inflammation
  caused by the release of mediators from lungs
  subjected to injurious mechanical ventilation
• Protective ventilation can lower concentration of
  cytokines in lung and plasma

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Cellular pathology of VALI

• Physical disruption stress failure
• gt40 mmHg, edema hemorrhage
• Mechanical activation of cellular pathways
  mechanotransduction
• physical force detected by cells and converted
  in biochemical signeals (proinflammatory
  mediators, cytokines)

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Mechanotransduction

• Stretch-activated ion channels
• Extracellular pathways between the matrix,
  integrin, and cytoskeleton
• Intercellular junctions
• Transcriptional and post-transcriptional
  regulations

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Prospects for pharmacotherapy

• After elucidation of the cellular
  mechanisms underlying VALI, we can design
  effective treatments to block mechanotransduction
  and its downstream consequences and further
  reduce deaths in patients with ARDS.

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Recommendations

• Protective ventilation is the only
  treatment or supportive modality that affects
  outcome in patients with ARDS. With few
  exceptions, for example patients with underlying
  disorders that would be exacerbated by
  hypercarpnia (eg, IICP), low tidel volume
  ventilation should be used routinely for patients
  with injured lungs.

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Thanks you