Definition and Overview
The Blalock-Taussig shunt is a procedure that connects the systemic to the pulmonary circulations (aortopulmonary shunt). It is a palliative procedure, meaning it does not treat the disease but only address the symptoms. The primary aim in palliative procedures is to improve the patient’s hemodynamic status, allowing growth until the patient is stable enough to undergo additional surgical procedure/s designed to treat the condition.
The Blalock-Taussig shunt is performed for patients with cyanotic heart conditions, where there is a lack of flow to the pulmonary bed, resulting in the lack of oxygenation in the body. Patients with this condition typically present with cyanosis, or a bluish discoloration of the skin.
Who Should Undergo and Expected Results
At present, the use of the Blalock-Taussig shunt has been decreasing as more and more surgeons perform neonatal and infant surgeries for the complete correction of congenital heart defects. However, it is still commonly used in patients with atresia (absent) or severe stenosis (narrowing) of the pulmonary artery, especially in patients with complex congenital heart defects, such as single ventricle malformations. It is also used in the staged reconstruction of patients with hypoplastic left heart syndrome (HLHS), particularly as part of the Norwood procedure. It may still be used in patients with Tetralogy of Fallot experiencing cyanotic spells, although it is less commonly performed for this indication nowadays.
As for the expected results, the procedure allows the blood to flow freely from the systemic to the pulmonary circulation, resulting in higher oxygen saturations and a decrease in diastolic blood pressure.
How is the Procedure Performed?
The Blalock-Taussig shunt is a connection between a systemic artery, typically the innominate or a subclavian artery, and the pulmonary artery. It may be performed via a thoracotomy (an incision on one side of the chest) or a median sternotomy (an incision in the midline, through the sternum). If the thoracotomy approach is chosen, it is usually performed on the side opposite the aortic arch. The sternotomy approach is best used for hemodynamically unstable patients.
Classically, the Blalock-Taussig shunt involves the transection or division of the subclavian artery, which is then connected to the pulmonary artery on one side. The main advantages of this method are no foreign material is used in the procedure, and the shunt can grow as the patient grows. Unfortunately, the procedure involves the sacrifice of the subclavian artery, which results in the atrophy of the upper extremity in many cases. In worst instances, it can result in limb loss due to the lack of blood supply and ischemia.
Because of these complications, numerous modifications were developed to make the procedure safer. The modified version makes use of a polytetrafluoroethylene (PTFE) graft to create the aortopulmonary connection. The innominate artery is typically selected as the proximal end (although the subclavian artery may also be used) while the distal end of the graft is connected to the pulmonary artery. Heparin is given during the procedure to prevent thrombosis and clot formation during clamping and anastomosis.
Aside from the preservation of blood flow to the arm, other advantages of modified Blalock-Taussig shunt over other forms of aortopulmonary shunts include the regulation of blood flow across the shunt and ease of shunt takedown upon reoperation.
Possible Risks and Complications
Several complications may occur during the Blalock-Taussig shunt procedure. Bleeding is always a risk since blood vessels are to be isolated and opened during the procedure. Aggressive dissection may result in damage to nearby structures, such as the phrenic nerve or the recurrent laryngeal nerve. This can result in symptoms such as breathing difficulty. Damage to lymphatic channels may also occur, resulting in chylothorax.
There may also be problems associated with the use of a synthetic material, such as an increased risk for infection. The use of a PTFE graft, specifically, can result in the leakage of serous fluid through the conduit, resulting in prolonged drainage times or seroma formation.
The placement of a shunt that is too small can result in an inadequate pulmonary flow whereas using a shunt that is too big can result in excess blood flow and pulmonary congestion. In some cases, the pulmonary artery may become distorted or stenotic after shunt insertion, especially if it is already small to begin with. Although it may not cause problems during or immediately after the operation, these complications may make subsequent surgery more difficult.
There are also instances when the patient is unable to tolerate the placement of a vascular clamp on the pulmonary artery during the procedure resulting in very low oxygen saturations or unstable hemodynamics. If any of these occurs, the vascular clamp must be removed immediately, and the procedure be performed under cardiopulmonary bypass.
Mortality during the procedure is low and is typically caused by an underlying disease.
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