What is the main mechanism causing respiratory distress, and how does it relate to the causes?

Respiratory distress results from ventilation-perfusion (V/Q) mismatch:

• Predominantly poor ventilation presents with respiratory distress - e.g. RDS, congenital pneumonia, meconium aspiration syndrome, transient tachypnoea of the newborn, pneumothorax, diaphragmatic hernia
• Predominantly poor perfusion presents with cyanosis - e.g. persistent pulmonary hypertension of the newborn (PPHN)

Clinical relevance. Understanding V/Q mismatch (poor ventilation -> distress; poor perfusion -> cyanosis) frames the differential diagnosis of neonatal respiratory disease.

More Detail

Mechanism of respiratory distress (V/Q mismatch)

Respiratory distress arises from ventilation-perfusion mismatch, with two broad patterns.

The principle

• Good gas exchange requires both adequate ventilation and perfusion; ventilation-perfusion (V/Q) mismatch causes hypoxia and distress.

Predominantly poor ventilation (present with respiratory distress)

• Respiratory distress syndrome (surfactant deficiency, premature).
• Congenital pneumonia (mostly acquired from the mother).
• Meconium aspiration syndrome.
• Transient tachypnoea of the newborn (delayed clearance of lung fluid).
• Pneumothorax (e.g. with artificial ventilation/aspiration).
• Congenital diaphragmatic hernia.

Predominantly poor perfusion (present with cyanosis)

• Persistent pulmonary hypertension of the newborn (PPHN) - pulmonary vascular resistance stays high, shunting blood away from the lungs.
• (Cyanotic congenital heart disease also presents with cyanosis.)

Use

• Categorising by the predominant problem (ventilation vs perfusion) and the clinical picture helps identify the cause.