Due to hypoxia in the uterus or after birth, the pulmonary arterioles constrict, leading to pulmonary hypertension. This causes a right-to-left shunt (through the foramen ovale and ductus arteriosus), known as persistent fetal circulation (PFC), also referred to as persistent pulmonary hypertension.

bubble_chart Auxiliary Examination

1. Chest X-ray shows cardiomegaly and hilar congestion, or manifestations specific to the underlying disease.
2. Electrocardiogram (ECG) reveals right ventricular hypertrophy, right axis deviation, and ST segment or T wave changes when myocardial damage is present.
3. Echocardiography can detect the presence and location of right-to-left shunting and exclude other cardiac anomalies.
4. Cardiac catheterization not only confirms the level of shunting but also measures pressures in the left and right heart and pulmonary artery, though it should not be used unless urgently needed.
5. Blood gas analysis can assess the degree of metabolic acidosis.

bubble_chart Diagnosis

1. History The infant often has a history of hypoxia such as asphyxia, hyaline membrane disease, meconium aspiration, polycythemia, or congenital heart disease.
2. Symptoms and Signs The infant exhibits unexplained cyanosis, restlessness, and respiratory distress immediately or shortly after birth. Approximately half of the infants may have a murmur heard at the left sternal border, caused by tricuspid regurgitation, which may be accompanied by tremor.
3. To determine whether the cyanosis is due to shunting or pulmonary disease, the infant can be given 100% pure oxygen to inhale. After 10 minutes, the oxygen partial pressure is measured. If it is due to shunting, the PaO₂ remains low or the cyanosis shows little improvement. To assess the presence of right-to-left shunting at the ductal level, the PaO₂ of the right radial stirred pulse and femoral stirred pulse blood can be measured separately. If the former is significantly higher than the latter, its presence can be confirmed. However, the absence of a difference does not completely rule out the possibility of this condition.

bubble_chart Treatment Measures

1. General treatment: Keep warm and maintain a quiet environment.
2. Oxygen therapy: Administer 100% pure oxygen to relieve pulmonary vasospasm. Mechanical ventilation may be used if necessary.
3. Medication: The α-adrenergic blocker tolazoline can be used, starting with a dose of 1mg/kg, administered via slow intravenous infusion over 10–15 minutes. If effective, the dose may be repeated after 1–2 hours. Gradually reduce the dose after significant improvement, with the total infusion generally not exceeding 5mg/kg. Side effects include hypotension and gastrointestinal bleeding. Combining with dopamine (infused at 5–10µg/kg per minute) is beneficial for preventing shock, maintaining blood pressure, and improving renal function.
4. Correct acidosis: Administer isotonic sodium bicarbonate solution for correction, which can be calculated based on the base excess (BE).
5. Symptomatic treatment: Use digitalis for heart failure, and perform partial exchange transfusion for polycythemia.