point where we are often able to determine whether a complete single-stage repair with low right ventricular pressure will be possible based on preoperative anatomy and physiology In particular, virtually all patients with a preoperative systemic oxygen saturation of 85% or higher will have a well-developed pulmonary vascular bed and be able to undergo single-stage complete repair However, in borderline cases, we continue to utilize the intraoperative flow study to assess the effective total pulmonary resistance after completion of the unifocalization and pulmonary artery reconstruction The indications for an intraoperative flow study in our practice now include patients with a preoperative oxygen saturation equal to or greater than 82% or who are above 2 years of age at the time of unifocalization If the flow study demonstrates a high pulmonary artery pressure (>25 to 30 mm Hg depending on age) during gradually increasing pulmonary blood flows (from 20% to 100% to 120% of a normal cardiac output), a central shunt is placed from the aorta to the unifocalized pulmonary arteries, aiming for a mean pulmonary artery pressure of 25 to 30 mm Hg, leaving the right ventricle untouched Closure using a fenestrated ventricular septal defect patch is not performed If the flow study demonstrates low pulmonary artery pressure (≤25 mm Hg) at physiologic levels of flow, intracardiac repair is performed Using these criteria, we rarely have a fully repaired patient whose right ventricular systolic pressure exceeds 50% of systemic systolic pressure Other groups have subsequently reported the value of the intraoperative flow study.33 When complete repair is performed, a cardioplegia needle is placed in the ascending aorta and the aorta is cross-clamped Cardioplegia is administered to achieve electromechanical silence A right ventriculotomy is performed and the intracardiac anatomy inspected The previously harvested autologous pericardium is trimmed to the appropriate size for ventricular septal defect closure and sutured in place If there is an interatrial communication, this is closed through a right atriotomy The aortic cross-clamp is removed During rewarming, the right ventricle-to-pulmonary artery conduit is sutured in place, performing the distal anastomosis first The proximal anastomosis is usually augmented with an anterior patch to maintain the proper orientation of the homograft valve (Fig 36.19) All suture lines are inspected to ensure hemostasis Transthoracic pressure-monitoring lines are placed in the left atrium and through the right atrium into the right ventricle The patient is weaned from cardiopulmonary bypass, a transesophageal echocardiogram is performed to assess ventricular function and inspect the integrity of the repair, and the venous cannulas are removed FIG 36.19 Complete unifocalization of major aortopulmonary collateral arteries (MAPCAs) (A) Complete repair, including closure of the ventricular septal defect and placement of a conduit from the right ventricle to the reconstructed central pulmonary artery (B) Unifocalization with placement of a central shunt from the ascending aorta to reconstructed pulmonary artery bed (From Mainwaring RD, Sheikh AY, Punn R, et al Surgical outcomes for patients with pulmonary atresia/major aortopulmonary collaterals and Alagille syndrome Eur J Cardiothorac Surg 2012;42:235– 240.) When a patient does not pass the intraoperative flow study or if it was determined in advance to perform unifocalization without complete repair, a central aortopulmonary shunt is placed to the unifocalized pulmonary arteries Before coming off bypass, a side-biting clamp is placed on the central portion of the reconstructed pulmonary artery and an expanded polytetrafluoroethylene conduit is anastomosed end-to-side to the pulmonary artery with running Prolene suture The clamp is released and hemostasis is ensured The length of the shunt is estimated and it is cut with a bevel to align with the lateral aspect of the ascending aorta A side-biting clamp is placed on the lateral aspect of the ascending aorta at the same level, after which the excluded portion of the aorta is incised and anastomosed to the shunt in end-to-side fashion with running Prolene suture A temporary hemoclip is left in place until cardiopulmonary bypass is weaned to assess the effect of the shunt on hemodynamics Shunt diameter is typically between 4 and 6 mm depending on the patient's weight and the overall caliber of the pulmonary vascular bed, with a goal mean pulmonary artery pressure of 25 to 30 mm Hg If necessary, clips are placed on the shunt to titrate the pressure to this level Central Aortopulmonary Connection (Aortopulmonary Window) In patients with complete dual-supply MAPCAs and central pulmonary arteries that arborize to all or essentially all lung segments, we perform an end-to-side aortopulmonary connection as the first procedure to facilitate growth of the pulmonary arteries The technique for this procedure is depicted in Fig 36.20 and was described previously.60 Briefly, through a median sternotomy and limited pericardial incision, the great arteries are dissected The main pulmonary artery and central left and right pulmonary arteries are mobilized Temporary neurovascular clips are placed on the branch pulmonary arteries, and the proximal main pulmonary artery is divided as close as possible to its connection to the right ventricle; the proximal end is oversewn or clipped if necessary The main pulmonary artery is explored to determine the best location for the anastomosis, taking care to avoid distortion of the right pulmonary artery where it passes behind the ascending aorta In most cases the anastomosis is to the left posterolateral aspect of the ascending aorta just above the sinotubular junction,