The primary pathophysiology of pulmonary hemorrhage is related to which of the following?

• A. Acute traumatic injury
• B. Right to left extrapulmonary shunting
• C. Sudden decrease in pulmonary vascular resistance
• D. Increase in systemic vascular resistance

Answer: (C)

Pulmonary hemorrhage in the neonate is driven by a sudden surge of blood flow into the lungs when pulmonary vascular resistance falls rapidly. This rapid drop allows more blood to reach the pulmonary capillaries quickly, raising capillary hydrostatic pressure and stressing the fragile alveolar–capillary membranes. The resulting capillary leakage can lead to blood spilling into the alveoli. In practice, events that abruptly reduce pulmonary vascular resistance—such as certain treatments or shifts in lung mechanics in a vulnerable infant—are the initiating factor for hemorrhage. Other scenarios, like trauma, or patterns of shunting and systemic resistance changes, explain related effects or consequences but do not represent the primary mechanism driving the hemorrhage.