Third Stage of Univentricle Hearts (Fontan Procedure)
The Fontan procedure is the third and last stage of the palliation procedure for UVH. The procedure is performed to divert the remaining systemic venous blood from the inferior vena cava to the pulmonary artery (Figure 5 ). This procedure is usually performed at around 1 to 5 years of age when restriction of patient activity is becoming problematic and size of the pulmonary arteries are sufficient to allow for a low PVR.13 The classic Fontan technique include creating an atriopulmonary anastomosis is made by isolating the right atrial chamber by closing the atrial septal defect and connecting the hypoplastic tricuspid valve to the inferior vena cava. Afterwards, the right atrial appendage would be anastomosed to the right pulmonary artery. It was later understood that better streaming the blood flow in the systemic venous pathway to the lungs could improve the patients’ hemodynamics. By doing so, complications related to progressive atrial dilation could be avoided. The operation was subsequently modified to what is known as the lateral tunnel technique. The right atrium was baffled with an intra-atrial patch, and the superior vena cava was sutured directly to the right pulmonary artery.13 The most recent modification of the Fontan procedure consisted of replacing the intra-atrial routing of the venous blood by inserting an extracardiac conduit between the inferior vena cava and the right pulmonary artery.14 The advantages of using an extracardiac conduit include avoiding multiple suture lines in the atrium that might serve as a substrate for reentrant tachycardias.15
Our criteria in selecting candidates that can be safely staged and are eligible for the Fontan procedure to ensure a high probability of success include a mean pulmonary artery pressure of less than 15 mmHg, pulmonary artery resistance index of less than 4 Wood units/m2, confluent pulmonary arteries with the diameter of the branches according to the patient’s bodyweight in the half size, systemic ventricular end-diastolic pressure of less than 15 mmHg, the absence of severe atrioventricular valve regurgitation unless it can be repaired or replaced, good systemic ventricular function, and the patient’s age should be more than three years.
The patient is usually positioned in a semi-Fowler position after the procedure to improve blood flow from the upper body to the right atrium. Early ambulation after surgery also increases venous return and cardiac output. Early extubation will also improve pulmonary blood flow and systemic oxygen delivery, provided that spontaneous breathing provides enough oxygenation and CO2 removal.16The optimal target for oxygen saturation after the Fontan Procedure is 95%. Low positive end-expiratory pressure and low mean airway pressure are ideal if the patient still needs ventilator support.
Regarding anticoagulant management, we start the patient on heparin as soon as possible. If there is no evidence of bleeding, heparin is administrated at an initial dose of 5-10 IU/kg/hour and titrated until the therapeutic level is achieved, indicated by a prothrombotic time of 60-80 seconds. In addition, we usually start the patient on 0,2 mg/kg/day of warfarin after extubation, where it is titrated every three days until therapeutic level is achieved, indicated by an international normalized ratio (INR) of 2.0-3.0.