Cell Injury Case Studies


CASE 3: Pulmonary Diffuse Alveolar Damage


Clinical History:

A 24-year-old man is involved in a motorcycle accident with left lower leg injury and laceration of the popliteal artery. Paramedics arrive at the scene and find that his skin is cool and clammy. His vital signs show pulse 110/min, respirations 24/min, temperature 36.2 C, and blood pressure 70/palpable. On arrival at the hospital his hematocrit is 18%. He is given transfusions of RBC's. His condition remains unstable and his peripheral blood oxygen saturation falls. He requires intubation with mechanical ventilation. The percentage of oxygen is increased to maintain saturations. His lungs become more difficult to ventilate.
  1. What is the mechanism for lung injury here?

    2. This is so-called "shock lung" with tissue damage potentiated by the high oxygen content of the inspired oxygen on mechanical ventilation. This is a form of generation of free radicals that potentiate cell injury.

  2. Explain the findings.

    3. The cellular damage, particularly to the alveolar epithelium and capillary endothelium, leads to an outpouring of fluid rich in protein, and this coalesces to a "hyaline membrane" seen here microscopically as the pink rim of material in alveoli. The alveoli are less distensible and more difficult to ventilate. This condition clinically is known as "adult respiratory distress syndrome" or ARDS, and it is the final common pathway for many forms of lung injury. Pathologically, the process is known as "diffuse alveolar damage" or DAD The combination of intra-alveolar fluid and interstitial fuid gives the patchy white appearance on radiographic studies. Normal well-aearated lung should be dark (radiographically, almost transparent).

  3. What is the resolution for this problem?

    4. If the underlying condition that caused the problem can be alleviated and lung function can improve, then recovery is possible. Otherwise, the condition is progressive and the patient dies.