Medicine
Pathophysiology of ARDS and Ventilator-Induced Lung Injury
Quick fact
ARDS has a mortality rate of 30-40% and the only proven therapy is protective mechanical ventilation, which paradoxically uses low tidal volumes that may appear 'under-ventilating' but reduce lung injury.
Why this is interesting
A ventilator that keeps a patient alive can also cause fatal lung damage—so how do doctors balance the two?
Read the full explanation
Understanding Pathophysiology of ARDS and Ventilator-Induced Lung Injury
ARDS is a sudden, severe lung inflammation that damages the alveolar-capillary membrane, causing fluid to leak into the air sacs, leading to profound oxygen exchange failure. To keep patients alive, doctors use a machine to push air in. But the lungs are stiff and fragile; the very act of pushing air can cause excessive stretching of the few healthy alveoli (like overinflating a balloon) and even shear forces when collapsed areas reopen. This is known as ventilator-induced lung injury (VILI), which further inflames the lungs, creating a vicious cycle.
A deeper explanation
The pathophysiology of ARDS begins with an initial insult (e.g., sepsis, pneumonia) that triggers a massive inflammatory response. Neutrophils and macrophages release cytokines, damaging the alveolar epithelium and capillary endothelium. This leads to increased permeability, flooding the air spaces with protein-rich fluid, forming hyaline membranes that impair gas exchange. When mechanical ventilation is applied, it can cause volutrauma (overstretching alveoli), barotrauma (high airway pressures causing pneumothorax), atelectrauma (repeated opening and closing of collapsed alveoli causing shear stress), and biotrauma (release of inflammatory mediators into the bloodstream, causing multi-organ failure). Protective ventilation strategies aim to minimize these forces by using low tidal volumes (to reduce overdistension) and adequate PEEP (to keep alveoli open, preventing atelectrauma). Understanding these mechanisms is why we treat ARDS not with aggressive ventilation but with a gentler approach—saving the lungs even at the cost of higher CO2 levels.