Ventilator Associated Lung Injury (VALI)

OVERVIEW

• mechanical ventilation with application of pressure to the lung, whether positive or negative, can cause damage known as ventilator-associated lung injury (VALI)
• VALI may occur in previously normal lungs or worsen pre-existing ARDS
• About 1 in 4 mechanically ventilated patients develop VALI, the risk is likely higher in ARDS patients
• Ventilator induced lung injury (VILI) is sometimes used as a synonym for VALI, but strictly speaking VILI is VALI when mechanical ventilation is the proven cause of lung injury

TYPES OF VALI

Ventilator Associated Lung Injury (VALI) can occur due to:

• volutramua
• barotrauma
• biotrauma
• recruitment/ derecruitment injury (atelectotrauma)
• shearing injury
• oxygen toxicity

Ventilated patients are also at risk of ventilator associated pneumonia (VAP)

MECHANISMS AND MINIMISATION STRATEGIES

Injury	Mechanism	Minimisation Strategy
Volutrauma	Non-homogenous lung injury Over-distension of normal alveolar units to trans- pulmonary pressures above ~30 cm H2O (that corresponds to approximate total lung volume) causes basement membrane stretch and stress on intracellular junctions.	Avoid over-distending the “baby lung” of ARDS: (a) Maintain Plateau Airway pressure under 30 cm H20 (b) Use Tidal volumes 6ml/kg (4- 8ml/kg) Good evidence to support this strategy (ARDSNet ARMA trial)
Barotrauma	Increasing the trans-pulmonary pressures above 50 cm H2O will cause disruption of the basement membranes with classical barotrauma
Biotrauma	Mechanotransduction and tissue disruption leads to upregulation and release of chemokines and cytokines with subsequent WBC attraction and activation resulting in pulmonary and systemic inflammatory response and multi-organ dysfunction	Protective lung ventilation strategies Use of neuromuscular blockers may ameliorate (ACURASYS trial)
Recruitment / Derecruitment Injury aka atelectotrauma	The weight of the oedematous lung in ARDS contributes to collapse of the dependant portions of the lung Repeated alveolar collapse and expansion (RACE) with tidal ventilation will contribute to lung injury.	Consider recruiting collapsed lung +/- employing an open lung ventilation strategy. This may be achieved by: (a) Ventilation strategies: Sigh / APRV / “Higher PEEP” (b) A recruitment manoeuvres: e.g. CPAP 40/40, or stepwise PCV (c) Prone Positioning (gravitational recruitment manoeuvre) Good theoretical support and case series / few trials inconclusive outcomes / meta-analysis supports high PEEP / proning supported by PROSEVA trial
Shearing injury	This occurs at junction of the collapsed lung and ventilated lung. The ventilated alveoli move against the relatively fixed collapsed lung with high shearing force and subsequent injury.
Oxygen toxicity	Higher than necessary FiO2 overcomes the ability of the cells to deal with free oxygen free radicals and leads to oxygen related free radical related lung injury. High FiO2 may contribute to collapse through absorption atelectasis.	Limit FiO2 through the use of recruitment, higher PEEP and accepting SaO2 / PaO2 that correspond the the “shoulder” of the oxyhaemoglobin dissociation curve (SaO2 88-94)

References and Links

LITFL

• CCC — Volutrauma
• CCC — Protective lung ventilation
• CCC — Open Lung Approach to Ventilation

Journal articles

• Frank JA, Matthay MA. Science review: mechanisms of ventilator-induced injury. Crit Care. 2003 Jun;7(3):233-41. Epub 2002 Oct 16. Review. PubMed PMID: 12793874; PubMed Central PMCID: PMC270664.
• Gajic O, Dara SI, Mendez JL, Adesanya AO, Festic E, Caples SM, Rana R, St Sauver JL, Lymp JF, Afessa B, Hubmayr RD. Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation. Crit Care Med. 2004 Sep;32(9):1817-24. PubMed PMID: 15343007.
• Mead J, Takishima T, Leith D. Stress distribution in lungs: a model of pulmonary elasticity. J Appl Physiol. 1970;28:596–608. [PubMed]
• Pinhu L, Whitehead T, Evans T, Griffiths M. Ventilator-associated lung injury. Lancet. 2003 Jan 25;361(9354):332-40. Review. PubMed PMID: 12559881
• Rocco PR, Dos Santos C, Pelosi P. Pathophysiology of ventilator-associated lung injury. Curr Opin Anaesthesiol. 2012 Apr;25(2):123-30. doi: 10.1097/ACO.0b013e32834f8c7f. Review. PubMed PMID: 22395439.