Persistent pulmonary hypertension of the newborn

SAQ 1 (10 marks)

A term male infant (birth weight 3.4 kg) born by emergency Caesarean section for fetal distress develops cyanosis and respiratory distress at 2 hours of life. Pre-ductal SpO₂ is 88% on 80% FiO₂; post-ductal SpO₂ is 72%. Chest X-ray shows clear lung fields with a normal heart size. [1]

a) What is the most likely diagnosis and what bedside finding supports it? (2 marks) — The pre–post ductal SpO₂ gradient of 16% (88% versus 72%) in the setting of refractory hypoxaemia with clear chest X-ray strongly suggests persistent pulmonary hypertension of the newborn (PPHN). The right-to-left ductal shunt produces the differential cyanosis. [1]

b) List four risk factors for this condition. (2 marks) — Risk factors include emergency Caesarean delivery without labour, perinatal asphyxia (fetal distress was noted antenatally), late-preterm or early-term gestation, and meconium aspiration, neonatal sepsis, or maternal SSRI use. [1]

c) What investigation is essential before starting inhaled nitric oxide, and why? (2 marks) — An echocardiogram is mandatory before iNO to exclude cyanotic congenital heart disease — particularly duct-dependent lesions where reducing PVR can steal systemic output through the ductus and precipitate cardiovascular collapse. The echo also confirms PPHN by estimating pulmonary artery pressure and visualising shunting. [4]

d) Outline your stepwise management of this infant. (4 marks) — First, optimise lung inflation and oxygenation with FiO₂ titrated to pre-ductal SpO₂ at or above 85% and gentle ventilation with permissive hypercapnia targeting pH 7.35–7.50. Second, correct metabolic derangements including glucose, calcium, temperature, and treat acidosis. Third, support systemic blood pressure with inotropes or vasopressors to keep mean BP above gestational age in weeks. Fourth, start inhaled nitric oxide at 20 ppm if OI exceeds 15 or SpO₂ remains below 85%, and refer for ECMO if OI exceeds 25–40 despite maximal therapy. [5]

SAQ 2 (10 marks)

A 36-week gestation infant born after meconium-stained liquor presents with severe respiratory distress. On 100% FiO₂, pre-ductal PaO₂ is 45 mmHg and post-ductal PaO₂ is 28 mmHg. Mean airway pressure is 14 cmH₂O. The infant's mean BP is 32 mmHg. [1]

a) Calculate the Oxygenation Index and interpret it. (2 marks) — OI = (MAP × FiO₂ × 100) ÷ PaO₂ = (14 × 1.0 × 100) ÷ 45 = 31. An OI of 31 indicates severe PPHN and warrants urgent discussion with an ECMO centre. [3]

b) Describe the pathophysiological vicious cycle in PPHN. (3 marks) — Failure of PVR to fall at birth drives blood through fetal channels (PFO, PDA, intrapulmonary shunts), bypassing the lungs and causing profound hypoxaemia. Hypoxaemia produces acidosis, which further constricts the pulmonary vasculature. Systemic hypotension lowers SVR below PVR, widening the right-to-left shunt and perpetuating the cycle. [1]

c) The mean BP is 32 mmHg. Why is this dangerous, and how would you manage it? (3 marks) — A mean BP of 32 in a 36-week infant is below the gestational-age target of at least 36 mmHg. Systemic hypotension drops SVR below PVR, worsening right-to-left shunting. Management includes cautious volume expansion (10 mL/kg normal saline) and inotrope or vasopressor support to raise systemic pressure above PVR. [7]

d) Name two adjunctive pulmonary vasodilators used when iNO is insufficient and their mechanism of action. (2 marks) — Sildenafil inhibits phosphodiesterase-5, prolonging the nitric oxide–cGMP vasodilatory pathway. Milrinone inhibits phosphodiesterase-3, raising cAMP to provide pulmonary vasodilation and inotropic support simultaneously. [1]