to the other lung, regardless of the systemic oxygen saturation, a neonatal procedure is performed Specifically, if the MAPCAs are favorable, single-stage complete repair is performed (see Fig 36.15), but if the MAPCAs are unfavorable, the ductus is stented or a systemic-to-pulmonary artery shunt is placed to the duct-dependent pulmonary artery and the patient is scheduled for unifocalization and assessment for intracardiac repair at 4 to 6 months of age Hemodynamic instability If the neonatal evaluation shows a systemic oxygen saturation more than 90% with failure to thrive, regardless of the anatomy of pulmonary blood supply, complete repair is performed, as the high pulmonary blood flow indicates that the circulation is adequate for the performance of a complete repair with low resistance If the neonatal systemic oxygen saturation is below 75%, neonatal unifocalization is performed regardless of the anatomy, either with or without simultaneous repair depending on the status of the MAPCAs and results of an intraoperative pulmonary flow study (see further on) All Other Patients (About 85% of Patients) Otherwise, patients are ideally scheduled for surgery at 4 to 7 months of age, with a plan to perform complete unifocalization This age range represents the ideal time with respect to minimizing morbidity Above this age, pulmonary vascular obstructive disease becomes a concern, potentially resulting is unacceptably high pulmonary artery pressure in unprotected lung segments even after an ideal surgical result Below this age, significant airway and pulmonary morbidity is more common due to immature tracheal and bronchial cartilage, with a concomitantly higher risk of prolonged hospitalization At the complete unifocalization procedure, either intracardiac repair will also be performed, making it a single-stage complete repair, or intracardiac repair will not be performed but instead a central systemic-to-pulmonary artery shunt will be placed At the time of unifocalization, a decision is made about proceeding with intracardiac repair (i.e., ventricular septal defect closure and right ventricle-topulmonary artery conduit placement) based on the size of the preoperative physiology and size of the pulmonary vessels, and sometimes on the basis of an intraoperative flow study, as described previously37 and further on Rarely, other palliative procedures or variations may be performed, including staged left and right unifocalization in the most severely affected patients It can be useful to group patients according to pattern of pulmonary blood supply to anticipate the likely operation The largest group, patients with largecaliber MAPCAs without segmental stenoses, usually undergo single-stage complete repair Patients with smaller MAPCAs and no segmental stenoses, 20% to 25% of the cohort, are typically able to have complete single-stage unifocalization but may or may not undergo complete repair at the same operation Patients with extensive segmental stenoses, approximately 10% of patients, typically undergo single-stage unifocalization with a central shunt, followed by complete repair 6 to 12 months later As noted previously, a similar proportion of patients have confluent central pulmonary arteries that arborize completely, with dual supply MAPCAs, and are initially treated with a surgical aortopulmonary window in the neonatal period Although this initial strategy is followed for patients with native anatomy at our institution, other surgical approaches may have been used in patients referred from elsewhere Although such patients may have reportedly undergone “repair” or “unifocalization,” they often require substantial pulmonary artery reconstruction consisting of augmentation, unifocalization of residual MAPCAs, and/or revision of prior surgical anastomosis of MAPCAs Occasionally, in extreme cases, staged unifocalization or pulmonary artery rehabilitation through a thoracotomy may be warranted Surgical Techniques Unifocalization Unifocalization and PA augmentation procedures are performed through a median sternotomy under general anesthesia with standard operative preparation If a thymus is present, it is resected to provide full exposure to the upper mediastinum The anterior pericardium is harvested and treated with glutaraldehyde for use as the ventricular septal defect patch Both pleural spaces are opened anterior and posterior to the phrenic nerve, and a series of stay sutures are placed 1 to 2 mm above the phrenic nerve to mark its position Inspection of the heart should include a survey of the coronary artery anatomy The dissection is begun by identifying the right and left branch pulmonary arteries, which are present in some 80% of cases These are typically quite diminutive, measuring 1 to 3 mm in diameter The plane between the aorta and main pulmonary artery is dissected to mobilize the pulmonary arteries fully The superior vena cava is dissected circumferentially and mobilized from the innominate vein to the cavoatrial junction to facilitate exposure of MAPCAs out to the lung parenchyma Traction sutures are placed on the lateral border of the aorta and on the superior vena cava; these are retracted laterally to open a window craniad to the left atrium (Fig 36.17) The transverse sinus is opened widely to reveal the descending aorta, where the majority of MAPCAs originate The airway is identified and the subcarinal space opened The many lymph nodes in this area are resected to facilitate exposure MAPCAs are identified in this subcarinal window and can be traced proximally to their descending aortic origins After finding the descending aorta, the origins of the remaining MAPCAs can be identified up and down the aorta Retro- and intraesophageal MAPCAs, which were observed in two-thirds of patients in a recent study from our center,4 should be sought on the lateral border of the aorta on the side contralateral to the aortic arch It is frequently necessary to remove the transesophageal echo probe to complete this dissection, particularly when a retroesophageal MAPCA is present Because the majority of intraesophageal MAPCAs have significant midsegment stenoses, they should not be used as unaltered conduits but should either be trimmed distal to the stenosis or augmented with a patch Dissection of MAPCAs is continued laterally to the entrance into the lung parenchyma It is important to perform this dissection prior to the administration of heparin, as doing so after heparinization can lead to intraparenchymal hemorrhage Complete hemostasis should be obtained throughout the operative field, with particular attention to the areas of lymph node resection This dissection exposes the full course of the MAPCAs, from the origin to the segmental branch points within the lung parenchyma, facilitating appropriate rerouting during unifocalization MAPCAs from head and neck vessels are similarly identified, dissected, and controlled, proceeding from the hilum or by tracking the MAPCA running along the tracheobronchial tree