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Dr. Alessandro Giardini
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The Norwood procedure is performed in the first week of life. It is the most complex cardiac operation in existence, performed on the smallest possible patient, to solve a circulatory problem that cannot be left untreated for more than a few days. For parents who have just received the diagnosis of hypoplastic left heart syndrome, understanding what this operation involves, why it is necessary, and what to expect in the days and weeks that follow is one of the most important things the clinical team can help with.
This post covers what happens at stage one: the surgical goals, the two main operative approaches, the postoperative period, and the period of recovery before the next stage.
In a baby with HLHS, the entire systemic circulation depends on the right ventricle maintaining flow through the ductus arteriosus to the aorta. That ductus is kept open in the neonatal period by prostaglandin therapy, but this is a temporary measure. Without surgery, the ductus will eventually close, systemic output will cease, and the baby will not survive.
The problem the Norwood procedure must solve has two components. First, there is no adequate outflow from the heart to the body: the aorta is tiny, often only two or three millimetres in diameter, and the aortic valve is either severely narrowed or completely atretic. Second, there needs to be a controlled, balanced source of blood flow to the lungs: too much pulmonary flow starves the body, too little causes blueness and poor body oxygentaion (cyanosis). Getting that balance right in an unstable neonate is the central surgical and postoperative challenge of stage one.
The Norwood procedure essentially rebuilds the outflow from the heart to the body by creating a new, larger aorta. The main pulmonary artery, which in a normal heart carries blood to the lungs, is divided from the pulmonary artery branches and used as the foundation of the new aortic root. It is sewn together with the tiny native aorta and supplemented with a patch of donor tissue to create a much larger vessel capable of carrying the right ventricle's output to the body. The aortic arch, which in HLHS is often severely hypoplastic, is also reconstructed at the same time.
Once the new aorta is established, blood flow to the lungs must be provided by an artificial shunt, since the main pulmonary artery has been taken out of its original circuit.
Two methods of providing pulmonary blood flow are in standard use, and families will often hear both discussed. The choice between them depends on the anatomy of the individual baby, the surgical team's experience and preference, and in some cases the baby's overall condition at the time of surgery.
The modified Blalock-Taussig shunt, commonly called the BT shunt, connects a systemic artery, usually a branch of the subclavian artery, to the pulmonary arteries via a small synthetic tube. Blood flows from the high-pressure systemic circulation to the lower-pressure pulmonary circuit. The shunt works throughout the cardiac cycle, including diastole, which means some blood is always flowing away from the systemic circuit to the lungs even when the heart is between beats. This diastolic run-off can compromise coronary perfusion and contribute to instability in the early postoperative period.
The Sano modification, or right ventricle to pulmonary artery conduit, provides pulmonary flow by placing a small synthetic tube directly from the right ventricle to the pulmonary arteries. Because flow in this conduit is driven by the systole (contraction) of the right ventricle rather than the diastolic pressure difference, diastolic run-off is eliminated and coronary perfusion is better protected. The trade-off is that a ventriculotomy, a deliberate incision in the right ventricle, is required to place the conduit, which may have implications for right ventricular function over time.
Large randomised controlled trial data from the Pediatric Heart Network's Single Ventricle Reconstruction trial found no significant difference in transplant-free survival between the two approaches at 12 months, though interstage mortality tended to be lower with the Sano shunt. Both techniques are in widespread use, and the decision is appropriately made by the surgical team in discussion with the family based on the individual anatomy.
At a small number of centres, a hybrid approach is used instead of the conventional Norwood procedure, particularly for very small or unstable babies for whom the full Norwood carries prohibitive risk. The hybrid procedure does not require cardiopulmonary bypass. It involves bilateral banding of the pulmonary artery branches to control pulmonary blood flow, and stenting of the ductus arteriosus to maintain systemic output, without reconstructing the aortic arch. The aortic arch reconstruction is then deferred to a comprehensive stage two operation at four to six months of age.
The hybrid approach has the advantage of avoiding bypass in the neonatal period, which may reduce neurological injury and improve early stability. The trade-off is a more complex second operation. The long-term outcomes of hybrid versus conventional Norwood palliation remain an area of active research.
The immediate postoperative period is managed in the cardiac intensive care unit. The baby will be intubated and ventilated, with multiple lines monitoring pressures directly within the heart and great vessels. The clinical team manages the delicate balance between pulmonary and systemic blood flow in these first hours and days, often requiring careful adjustment of ventilation, oxygen levels, and vasoactive medication.
The average hospital stay after stage one palliation is four to six weeks, though this varies considerably depending on how the baby recovers. Some babies are discharged in three weeks. Others have a more complex course, requiring longer ventilation, additional interventions, or management of postoperative complications such as pleural or pericardial effusions, arrhythmias, or feeding difficulties.
Before discharge, parents are taught interstage monitoring: how to measure oxygen saturations, recognise early warning signs of deterioration, and when to call the hospital. This training is not optional and is as important as the surgery itself for what comes next. The interstage period is covered in detail here.
Stage one mortality in experienced high-volume centres is now in the range of 10 to 15%. Several factors are associated with higher risk: low birth weight, prematurity, severe mitral or tricuspid valve abnormalities, significant tricuspid regurgitation, intact or highly restrictive atrial septum, and the presence of significant extracardiac anomalies. Centres that perform high volumes of HLHS surgery have consistently better outcomes than lower-volume programmes, and this is one reason why centralisation of this surgery at specialist centres is important.
Families should know that the operation itself is only the beginning. The weeks at home between stage one discharge and the Glenn procedure represent a period of significant risk. Active engagement with interstage monitoring, and prompt contact with the cardiac team when concerns arise, is as much a part of the treatment pathway as the surgery.
Most centres aim to perform stage one in the first three to seven days of life, once the baby has been stabilised on prostaglandin and the surgical and anaesthetic team is ready. In some cases surgery is needed sooner if the baby is deteriorating despite medical management. The timing is determined by the clinical team based on the baby's condition.
No. Babies in the cardiac intensive care unit after the Norwood procedure are kept fully sedated and analgesed while they are on the ventilator. Comfort and pain management are central priorities in the postoperative care, and the nursing and medical team monitor this continuously.
The surgical team will perform echocardiography in the early postoperative period to assess heart function and the anatomy of the repair. Clinical signs including oxygen saturations, blood pressure, urine output, and the baby's overall colour and tone all reflect how the circulation is performing. The team will explain what they are seeing and what targets they are aiming for at each stage of recovery.
Author: Dr. Alessandro Giardini, MD, PhD, Consultant Paediatric Cardiologist
Written 22/06/2026