ARDS
Picture the lungs' millions of air sacs as tiny balloons lined with a film that keeps them open and dry. In ARDS, a wave of inflammation damages the delicate barrier between air sac and blood vessel, and fluid leaks in from all over both lungs. The balloons flood and collapse, oxygen can no longer cross, and the person becomes severely short of breath with dangerously low blood oxygen — like trying to breathe through waterlogged sponges.
ARDS is not itself a primary lung disease but a reaction to some other serious insult: most often severe pneumonia or widespread infection (sepsis), but also major trauma, inhaled toxins, aspiration of stomach contents, or massive transfusion. The injury is diffuse — affecting both lungs widely rather than one patch — and develops quickly, within about a week of the triggering event. On a chest scan the flooded lungs look white on both sides, and the hypoxemia is stubbornly resistant to oxygen alone.
The cornerstone of care is to support the failing lungs gently while the underlying cause is treated, buying time for the inflammation to settle and the barrier to heal. This means low tidal volumes to avoid stretching injured tissue, adequate positive end-expiratory pressure to keep air sacs open, and prone positioning in severe cases. An honest caveat: ARDS remains serious, with significant mortality, and survivors may take months to recover lung function and strength — but careful supportive care meaningfully improves the odds.
Two days after surgery for a perforated bowel, a man develops sepsis and then breathlessness; his chest X-ray turns white on both sides and his oxygen stays low despite a high-concentration mask, the picture of ARDS.
Widespread lung flooding with oxygen-resistant hypoxemia is the signature of ARDS.
The current (Berlin) definition grades ARDS as mild, moderate, or severe by how low the oxygen level is relative to the inspired oxygen, measured with positive end-expiratory pressure applied.