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should be part of routine preoperative evaluation of the child with fUVH prior to the Fontan procedure In particular, the development of venovenous collaterals following the SCPC or potential venovenous collaterals after the Fontan is important should there be unexplained hypoxemia after surgery Also, many patients develop aortopulmonary collaterals following the SCPC The precise etiology of their presence and size is unknown but speculated to be related to prolonged hypoxemia, inflammation, and smaller pulmonary artery size.257–259 There is considerable controversy regarding intervention on these vessels at the time of pre-Fontan assessment.260,261 Although aortopulmonary collaterals may increase pulmonary artery pressure, volume load the ventricle, and complicate the conduct of cardiopulmonary bypass and surgery, a large retrospective review of 539 patients concluded that the variable practice of coiling collaterals preFontan did not lead to a shorter length of stay or late outcomes following Fontan.21 Table 71.9 Important Elements in the Pre-Fontan Evaluation Hemodynamics Systemic blood flow Pulmonary blood flow Pulmonary artery pressure Atrial pressure/end-diastolic pressure Systemic and pulmonary vascular resistance Pressure gradients: cavoatrial junction, atrial septum, pulmonary arteries, pulmonary veins, atrioventricular valve, ventricular outflow tract, aortic arch Valvar regurgitant fraction Anatomy Superior caval vein Inferior caval and hepatic veins Pulmonary arteries Ventricular outflow tract Aortic arch Other Ventricular function Atrioventricular valve regurgitation Venovenous collaterals Modality Cath, CMR Cath, CMR Cath Cath Cath Cath, CMR, echo CMR Cath, CMR, CT, echo Cath, CMR, CT, echo Cath, CMR, CT, echo Cath, CMR, CT, Echo Cath, echo, CMR Cath, echo, CMR Cath, CMR, CT Aortopulmonary collaterals Cath, CMR, CT Cath, Cardiac catheterization; CMR, cardiac magnetic resonance; CT, computed tomography; echo, echocardiography Traditionally cardiac catheterization has been used to evaluate the great majority of factors shown in Table 71.9 CMR may be a safe alternative to angiography in an appropriate subset of low-risk preoperative Fontan patients; however, most centers still routinely perform preoperative catheterization.262,263 In summary, a multimodal approach should be utilized and customized to the individual patient.264,265 Surgical Strategies Extracardiac Fontan Lateral tunnel Fontan Extracardiac Fontan with cavoapical juxtaposition Benefits and risks of fenestration The Fontan is the last planned operation in the Fontan pathway (see also Chapter 68) and is nearly always a completion Fontan, which follows a superior cavopulmonary connection The completion Fontan separates systemic and pulmonary venous drainage and restores in-series circulation, eliminating hypoxemia The Fontan pathway can be completed using a lateral tunnel or extracardiac conduit In the current era, the timing of the completion Fontan is not critical and in general occurs at 18 months to 4 years of age By 2 years of age, the pulmonary vasculature is developed such that the cardiac output can be accommodated at a modest elevation of central venous pressure The type of completion Fontan is dictated by the kind of SCPC performed In general, a lateral tunnel Fontan is chosen after hemi-Fontan whereas an extracardiac Fontan follows a bidirectional Glenn shunt (Figs 71.11 and 71.12; Video 71.3).266,267 FIG 71.11 The extracardiac Fontan is constructed using a tube graft to connect the inferior vena cava to the pulmonary arteries (From Kogon B Is the extracardiac conduit the preferred Fontan approach for patients with univentricular hearts? The extracardiac conduit is the preferred Fontan approach for patients with univentricular hearts Circulation 2012;126:2511–2515.)