First Stage of Univentricular Hearts
Blalock-Taussig-Thomas Shunt (BTTS)
BTTS represents the first stage of univentricular palliation surgery in patients with restricted pulmonary blood flow. This procedure allows the growth of pulmonary arteries, where it regulates pulmonary blood flow to the lungs until the size of the pulmonary artery is suitable for the second stage of univentricular palliation surgery. The classic BTTS is a direct anastomosis between the transected subclavian artery (or the innominate artery) and the pulmonary artery (Figure 1 ). It requires extensive surgical dissection where it sacrifices the subclavian artery.6  The main disadvantages of classic BTTS include long operative dissection time, phrenic nerve injury, technical difficulties during the takedown, as well as possible arm ischemia. In 1975, this technique was modified by Marc R. de Leval and his colleagues, where a polytetrafluoroethylene (PTFE) graft was used to interpose between the subclavian artery and the ipsilateral pulmonary artery (Figure 2 ). Since this modification, the procedure is now more popularly known as the modified BTTS. PTFE conduits are considered ideal compared to Dacron because they have smaller pore sizes that limit ingrowth of tissue, yet allowing for fibroblastic incorporation to bind the conduit to its surrounding structures.7
To maximize postoperative outcomes of the modified BBTS, a few things regarding perioperative management such as surgical consideration as well as strategies to deal with over-shunting and under-shunting must be considered. Surgical considerations include the approach to apply the modified BTTS. An approach through median sternotomy gives the surgeon exposure to the right subclavian artery. It will also expand the surgical field and allows the surgeon to initiate cardiopulmonary bypass if needed. The approach through sternotomy is correlated to the extended use of mechanical ventilatory support, the length of stay in the intensive care unit and hospital, as well as a higher mortality rate. Meanwhile, the thoracotomy approach provides ease in creating a proximal anastomosis beyond the bifurcation of the innominate artery. The thoracotomy approach will lead to the need for a more extended graft. The diameter of the graft becomes less critical in estimating shunt resistance so that the flow can be a problem. A  longitudinal arteriotomy incision in the subclavian and pulmonary arteries provides a wider circumferential area of the anastomosis for a larger shunt size. This technique proves to be more beneficial for hypoplastic pulmonary arteries. Pulmonary artery distortion at the anastomotic site is also less common with the longitudinal incision technique. Using a smaller needle size of 8/0 polypropylene will help provided better anastomosis and less bleeding from the needle hole.8
The basic principle to deal with over-shunting and under-shunting include balancing Qp:Qs by decreasing systemic vascular resistance (SVR) and increasing pulmonary vascular resistance (PVR) in modified BTTS to achieve an oxygen saturation of 70-85%. Strategies to increase the PVR include reducing the fraction of inspired oxygen (FiO2) to 0.21, avoidance of hyperventilation with targeted permissive hypercapnia, administration of high PEEP (PEEP 6-8), and maintaining blood pH 7.35-7.40. Evaluation of lactic acid and arterial blood gas may be done every 4-6 hours. Some inodilator are practical and can be used to decrease SVR. Dobutamine, milrinone or levosimendan may be considered while maintaining a diastolic blood pressure of over 25 mmHg. Administration of nitroglycerin can be considered if blood pressure is still high after using the inodilator.
After establishing the signs of under-shunting (oxygen saturation <70%, despite being given FiO2 > 0.60), we must first exclude the cause of under-shunting, especially shunt thrombosis where urgent echocardiography is needed to evaluate shunt patency. Respiratory system failure, such as displaced endotracheal tube, obstructed endotracheal tube, pneumothorax, and failure of hemodynamic support and equipment may also cause under-shunting. If those mentioned above are already excluded, strategic management include increasing FiO2 to achieve an oxygen saturation of 70-85%, avoid acidosis, and keeping blood pH around 7.40 to 7.45. Adequate volume status must be ensured by titrating fluid slowly according to the patient’s response with 5 ml 5% albumin. If the blood pressure is low, consider starting vasoconstrictors, such as norepinephrine or epinephrine. In addition, a pulmonary vasodilator (sildenafil and inhaled nitric oxide) may be needed to decrease PVR.8
Pulmonary Artery Banding (PAB)
PAB represents the first stage of univentricular palliation surgery in patients with unrestricted pulmonary blood flow. PAB aims to decrease pulmonary artery pressure and pulmonary vascular resistance to levels suitable for future univentricular palliation surgery. The golden period for performing PAB is considered to be 2 to 4 weeks of age. By this time, the neonatal pulmonary vascular resistance decreases, allowing for a tighter band.9
A median sternotomy approach was used for PAB. We use Mersilene tape with 5 mm width (Ethicon Inc., Somerville, NJ, USA) to band the pulmonary artery (Figure 3).  To prevent migration, the tape was fixated with two 6/0 Polypropylene stitches. As a guide, the Trusler formulae (for univentricle hearts: 22 mm + weight in kg) are used as the first steps, then finer adjustments being made by systemic O2 saturation (75 - 85%, with inspired oxygen fraction 0.50) and distal PAP (Target distal PAP 50% or the optimal mean PAP < 15 mmHg).9