Second Stage of Univentricular Hearts
The goal of the second-stage procedure of UVH is to divert systemic venous blood from the superior vena cava directly into the pulmonary vascular bed (Figure 4) , allowing for effective pulmonary blood flow while reducing volume load on the single ventricle to allow for favourable ventricular remodelling, which improves the patients’ outcomes.10
The bidirectional cavopulmonary shunt (BPCS) or Hemi-Fontan procedure is usually performed when the pulmonary arteries have grown adequately to allow adequate pulmonary blood flow with low PVR, which is usually between 2 to 6 months.11 In cases where the modified BTTS or PAB is performed first, reassessment to measure pulmonary artery size adequacy and pulmonary artery resistance index will be carried out 6 to 12 months later using cardiac catheterization or multi-slice computed tomography (MSCT).
The selection of the second-stage shunting procedure determines the technique utilized for the completion of the Fontan procedure. When a BCPS is used, an extracardiac completion Fontan is performed, as there is no point in reconnecting the superior vena cava to the right atrium after a BCPS. Patients with Hemi-Fontan modifications have extremely relevant anatomy for completion by the lateral tunnel Fontan operation, thus preferably used in these patients.12 The criteria for conducting BCPS or the Hemi-Fontan procedure at our centre include a mean pulmonary artery pressure of less than 18 mmHg and a pulmonary artery resistance index of less than Wood units/m2, with confluent pulmonary arteries and making sure the pulmonary artery size is according to the half size of the patient, which depends on body weight. Usually, in cases of UVH in BCPS, atrial septectomy will be performed if a restrictive atrial septal defect is suspected.
Postoperative management include positioning of the patient, where we usually position the patient in a semi-Fowler position to improve blood flow from the upper body to the right atrium. Early extubation helps improve pulmonary blood flow and systemic oxygen delivery as well as avoid needless sedation to improve spontaneous breathing. Modest hypercarbia of pCO2 ± 45 mmHg is acceptable as it enhances cerebral vasodilation and reduces the superior vena cava pressure. The target of saturation oxygen for BCPS/Hemi-Fontan patients is 85%. We typically give inotropics such as dobutamine to improve stroke volume in patients with poor contractility. Pulmonary vasodilators such as milrinone or oral sildenafil (if the patient can tolerate oral feeding) may be given. Patients with bilateral BCPS or concomitant reconstruction of pulmonary artery branches are usually given 5 mg/kg of acetylsalicylic acid in our centre.