Duct-dependent congenital heart disease: SAQ

This baby has duct-dependent systemic circulation, most likely critical coarctation of the aorta or interrupted aortic arch. The history of a well baby discharged on day 1 who collapses on day 3 is the classic duct-dependent presentation: the ductus arteriosus was perfusing the lower body, and it has now closed. The weak femoral pulses, the large arm-to-leg blood pressure differential of 30 millimetres of mercury, the severe metabolic acidosis, and the hypoglycaemia together confirm a left-sided obstructive lesion in cardiogenic shock. The immediate priority is to start prostaglandin E1 to reopen the duct, correct the hypoglycaemia, and cover sepsis while arranging echocardiography and transfer. [1] [3]

Question 1 (10 marks)

Outline your immediate assessment and resuscitation plan for this baby, including the specific drug therapy you would start and why. [1]

Begin with an airway, breathing, and circulation assessment and recognise that this baby is in critical condition. He is in cardiogenic shock with severe metabolic acidosis, prolonged capillary refill, tachycardia, grunting, and hypoglycaemia. The first interventions run in parallel: gain intravenous access, check and correct the glucose, and send a venous gas, blood culture, full blood count, and electrolytes. Give a bolus of 2 millilitres per kilogram of 10 percent dextrose for the hypoglycaemia and a cautious 10 millilitres per kilogram of isotonic saline only if shock is profound, because the underlying problem is obstructed blood flow rather than volume depletion. [1]

Start prostaglandin E1 (alprostadil) immediately at 0.01 micrograms per kilogram per minute intravenously and titrate up to 0.05 micrograms per kilogram per minute. The rationale is that this baby has a left-sided duct-dependent lesion where the closed ductus arteriosus was the only route for systemic blood flow to the lower body. Reopening the duct restores perfusion, improves the acidosis, and buys time for definitive surgery. Do not wait for the echocardiogram to start the infusion. [1]

Anticipate the side effects of prostaglandin E1, which include apnoea in approximately 10 percent of treated neonates, hypotension, fever, and flushing. Have intubation equipment ready and be prepared to electively intubate, especially if the baby needs transfer. Cover sepsis with empiric antibiotics because sepsis mimics and coexists with duct-dependent congenital heart disease, and confirm the anatomy with echocardiography as soon as the baby is stabilised. [2]

Question 2 (10 marks)

Describe the pathophysiology of why this baby was well on day 1 and collapsed on day 3, and outline your plan for transfer and definitive management. [3]

In fetal life the placenta provides oxygen and the ductus arteriosus shunts blood from the pulmonary artery to the aorta, bypassing the high-resistance lungs. In a baby with a left-sided obstructive lesion such as critical coarctation, the right ventricle pumps blood through the ductus arteriosus into the descending aorta, perfusing the lower body. While the duct is open this works perfectly, and the baby looks well and feeds normally. [1]

At birth the cord is clamped, the lungs expand, oxygen tension rises, and the ductus arteriosus begins to close functionally within hours and anatomically over the following days. By day 2 to 5 the anatomical closure is complete, the shunt through the duct ceases, and the lower body loses its blood supply. The baby develops metabolic acidosis from tissue hypoperfusion, shock from loss of cardiac output, and the femoral pulses become weak or absent. This explains the characteristic day-2-to-5 collapse pattern that is the fingerprint of duct-dependent congenital heart disease. [3]

For transfer, once the baby is stabilised on prostaglandin E1 with adequate perfusion and a correcting acidosis, arrange a dedicated neonatal transport team. Electively intubate before the transfer because apnoea from prostaglandin E1 can occur unpredictably en route. Continue the prostaglandin infusion throughout the transfer and monitor saturation, heart rate, and blood pressure continuously. The destination is a cardiac surgical centre where an echocardiogram will confirm the anatomy — most likely critical coarctation or interrupted aortic arch — and the cardiac surgeons will plan definitive repair. The prostaglandin infusion continues from the moment it is started until the definitive surgery is undertaken. [2] [3]