Ventilator - Induced Lung Injury

By Neil R. MacIntyre, MD, FCCP

Objectives

Understand the concept of ventilator-induced lung injury (VILI).
Understand the role of overdistention and underrecruitment in VILI.
Understand the mechanisms of injury in VILI.
Understand ventilator management strategies to minimize VILI.
Understand new approaches to managing VILI.

Key words

lung injury; lung-protective ventilatory strategies; mechanical ventilation; overdistention; recruitment; surfactant

Abbreviations

APRV = airway pressure release ventilation; FIO₂ = fraction of inspired oxygen; HFV = high-frequency ventilation; I:E = inspiratory to expiratory; NIH = National Institutes of Health; PEEP = positive end-expiratory pressure; PPV = positive pressure mechanical ventilation; PV = pressure volume; TNF-a = tumor necrosis factor a; VILI = ventilator-induced lung injury; VT = tidal volume

It has been known for decades that high levels of positive pressure mechanical ventilation (PPV) can physically rupture alveolar units and produce extra alveolar air.^1,2 By the 1950s, it also became apparent that high levels of inspired oxygen could also produce lung injury through the formation of toxic oxygen radicals.³ In the 1970s, elegant experiments by Webb and Tierney⁴ clearly demonstrated two additional important concepts: First, distending pressure and volume above normal maximums but below those required for alveolar rupture could also produce a lung tissue injury characterized by lung edema, surfactant abnormalities, inflammation, and hemorrhage. Second, preventing cyclical alveolar collapse/reopening could significantly reduce this lung injury (Fig 1). An emerging concept over the last decade is that overdistention (or stretch) injury in the lung is associated not only with physical lung injury but also with the production of a number of inflammatory cytokines.^5-14 This cytokine release creates not only local inflammation, but also systemic inflammation and organ dysfunction elsewhere.¹⁵

The remainder of this chapter will be divided into two parts. The first part will review the mechanisms of the lung injury associated with overdistention and cyclical alveolar collapse. This is the injury commonly referred to as ventilator-induced lung injury (VILI). The second part will review current (and potentially future) management strategies that have been designed to minimize VILI.

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