Abstract
Historically, the Blalock Taussig (BT) shunt has been an off-pump procedure. For the last two decades, the number of BT shunt operations has come down globally with the adoption of neonatal early corrective surgery. BT shunts are still performed for augmentation of pulmonary arterial (PA) growth or as a part of univentricular palliation. Many infants do not tolerate PA branch clamping while undergoing the graft to PA anastomosis, necessitating institution of cardiopulmonary bypass (CPB). Since the threshold to go on CPB for shunt placement is quite low at most institutions, our technical modification described can avoid deleterious effect of CPB. Our point of interest is to maintain lung perfusion by adopting few principles of off-pump coronary artery bypass surgery.
Keywords: Cardiopulmonary bypass(CPB), BT shunt, Intracoronary shunt
Introduction
The first Blalock Taussig (BT) shunt was done on 29th November 1944 by Dr. Alfred Blalock and his team at Johns Hopkins Hospital, Baltimore, Maryland, USA. Several modifications to this original operation took place since then and alternative approaches have been adopted like left/right lateral thoracotomies and median sternotomy. All the modifications describe occlusion of pulmonary artery (PA) branch partially or totally while suturing the graft to PA. Anesthesiologists maintain hemodynamics during this phase of surgery by maintaining adequate preload, modifying afterload, modifying pulmonary vascular resistance, and avoiding hypoxia, hypercarbia, acidosis, and sympathetic stimulation [1].
We describe hereunder a technique of maintaining adequate perfusion of the lungs during this phase of surgery.
Technique
After the standard median sternotomy procedure and vertical pericardiotomy, the innominate artery is isolated for the systemic end of the shunt. The segment of the right PA between the superior vena cava and ascending aorta is dissected free from surrounding structures. The line of anastomosis is marked on its superior surface, which is usually less than half the circumference of the graft (usually 4–6 mm). After completion of anastomosis of systemic artery (innominate artery) side of the shunt, the innominate artery is clamped at the base of the anastomosis. Doubly looped silicone vascular slings in older infants, or silk threads in neonates, are placed on either side of proposed incision on the right PA. Heparin is given to maintain activated clotting time of 180–200 s. The right PA is clamped on either side, near the slings, and saturations are noted. This works as a check clamp. Stab incision is made on the right PA and extended along the proposed line of anastomosis using microscissors. The intracoronary shunt (2.5 mm or 3 mm) is inserted into the incision. Once the shunt is in position inside the right PA, a slight traction on twice-looped slings ensures a bloodless field (Figs. 1 and 2). The clamps on either side are removed. Soon after the clamps are removed, usually saturations improve, almost equaling to pre-clamp saturation levels.
Fig. 1.
Novel technique of conducting systemic to pulmonary artery shunt. 3-mm intra-coronary shunt is placed within the RPA and secured with vascular slings, PTFE shunt to RPA anastomosis is carried out in a clear bloodless field and with hemodynamic stability. a Inset shows a detailed pictorial depiction of our novel technique. Ao, aorta; MPA, main pulmonary artery; RPA, right pulmonary artery; ICS, intracoronary shunt; SVC, superior vena cava; RA, right atrium; RV, right ventricle; LV, left ventricle; LA, left atrium
Fig. 2.
Intra-operative image of our novel technique of systemic to pulmonary artery using intracoronary shunt in RPA. R, right side; L, left side; Ao, aorta; MPA, main pulmonary artery; RPA, right pulmonary artery; ICS, intracoronary shunt; SVC, superior vena cava; RA, right atrium; RV, right ventricle; LV, left ventricle; LA, left atrium
Anastomosis of graft to the right PA is completed. Before the last loop of the suture is tightened, intracoronary shunt is pulled out after loosening the slings. A clamp on the innominate artery is removed and the suture tightened after a few seconds to allow de-airing. We used this technique of maintaining lung perfusion during construction of a modified BT shunt in 3 patients in the previous 1 year. There was no hemodynamic instability throughout the procedure in all the 3 cases. We choose to use larger shunts if branch PA is of good size, irrespective of age and weight of the patient, because in our experience managing a smaller shunt, with added risk of shunt thrombosis and pulmonary blood under-flow, has a much more disastrous outcome than shunt over-flow with larger shunts. Therefore, our 1st patient, even at 3 months old weighing 4.1 kg, received a 4-mm shunt because of a branch PA of 5 mm. The 2nd patient received a 3.5-mm shunt with a branch PA of 4 mm, at 2 months of age and weighing 3.6 kg. In our 3rd patient, even at 5 months old weighing 5 kg, we were compelled to place a 3-mm shunt graft due to hypoplastic branch PA anatomy measuring 3–3.5 mm. This kid with tetralogy of Fallot (TOF) presented to us with a cyanotic spell and his unfavorable anatomy made us opt for systemic to PA shunt procedure, instead of total correction. The central shunt for this patient was not opted to avoid chances of on-table spell episode, needing institution of cardiopulmonary bypass (CPB), when the main PA was supposed to be clamped during pulmonary end anastomosis.
All 3 cases had good post-operative shunt flow, none required on pump conversion, and no cases required re-exploration for bleeding or any shunt-related technical reasons (Table 1).
Table 1.
List of three patients who underwent our novel technique of systemic to pulmonary artery shunt using intracoronary shunts, their indication, and outcome of surgery. DORV, double outlet right ventricle; TOF, tetralogy of Fallot; PTFE, polytetrafluoroethylene
| Age (in months) |
Weight (kilograms) |
Diagnosis | Branch PA size to which shunt anastamosed (millimeters) |
PTFE graft (millimeters) |
Intracoronary shunt size (millimeters) |
Pre-operative Oxygen saturation at room air (percentage) |
Post-operative Oxygen saturation at room air (percentage) |
Outcome |
|---|---|---|---|---|---|---|---|---|
| 3 | 4.1 | Double outlet right ventricle (DORV), non-routable ventricular septal defect (VSD), pulmonary atresia, patent ductus arteriosus (PDA) | 5 | 4 | 3 | 65 | 80 |
Discharged Under follow-up |
| 2 | 3.6 | Tricuspid atresia, pulmonary stenosis | 4 | 3.5 | 3 | 58 | 78 |
Discharged Lost to follow-up |
| 5 | 5 | Tetralogy of Fallot (TOF), hypoplastic branch pulmonary artery, coronary crossing right ventricular outflow tract (RVOT), in cyanotic spells | 3–3.5 | 3 | 2.5 | 60 | 84 | Discharged. Succumbed after a month, due to aspiration |
Comments
Traditionally, BT shunt is an off-pump procedure, though many programs do it employing CPB. Over the years, early mortality has come down and is in the range of 4.5–8% [2]. CPB-assisted modified BT shunt has higher mortality in the first 48 h [3]. CPB has been used in an unstable baby or when a baby does not tolerate clamping; 7% of babies needed CPB support to do a modified BT shunt [4]. Hemodynamic instability happens mainly at the time of branch PA clamping due to increasing desaturation and marked acidosis ending with bradycardia and hypotension. It has been shown, especially in neonates, that CPB increases mortality and morbidity [5] due to susceptibility to post-operative bleeding, risk of volume overload, exaggerated inflammatory response, change in lung dynamics, and increasing pulmonary vascular resistance.
Intracoronary shunts, which have been used widely in off-pump coronary artery bypass surgeries, help in avoiding clamps and clamp-related injuries on fragile neonatal PAs, more accurate placement of pulmonary arteriotomy without clamp. Intracoronary shunt also provides a bloodless field, prevent taking of bites through the posterior wall, and allow unhurried suturing. Experimental studies have shown flow through the intracoronary shunt depends on perfusion pressure. Shunts of 2.5 mm and 3 mm can provide flow of average 50 ml/min at 50 mmHg pressure [6].
Intracoronary shunts placed in the left PA during a modified BT shunt through left thoracotomy in patients with ductus-dependent lesions can avoid compromise of ductal flow while clamping.
Results of patent ductus arteriosus (PDA) stenting are promising enough to reduce the number of systemic to PA anastomosis in recent years [7]. We consider only those cases for surgical palliation who are not amenable for right ventricle outflow tract (RVOT)/PDA stenting.
Conclusion
Our technique of construction of systemic to pulmonary artery shunt, using an intracoronary shunt to maintain pulmonary blood flow, may eliminate the need for institution of cardiopulmonary bypass, with its consequent detriments, while clamping the pulmonary artery. Our technique, simply put, is an extrapolation of a technique from the practice of adult cardiac surgery. It is a simple, reproducible, and cost-effective modification that increases the safety of the conduct of systemic to pulmonary artery shunt/BT shunt. Anastomosis can be done leisurely and taught to residents. All our operated cases, using this new modification, had behaved well intra-operatively and had good early post-operative recovery.
Funding
None.
Declarations
Ethics committee approval
This study was approved by the institutional ethics committee.
Informed consent
Obtained as per Institutional ethics committee guidance.
Human and animal rights
No humans or animals were harmed in our conduct of work nor any of their rights were violated.
Conflict of interest
The authors declare that they have no conflict of interest.
Footnotes
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
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