Discussion

After a decade and over a hundred cases under analysis, the anterior mini thoracotomy approach has become our primary surgical strategy for closure of patent ductus arteriosus in preterm infants. According to the research data for our entire patient cohort, we can speculate that this surgical procedure is particularly helpful for babies with high frequency ventilation support for whom a lateral decubitus position is not recommended. The most important advantages of this surgical approach to close patent ductus arteriosus in premature infants is that the patient is placed in the supine position with the left chest elevated for an anterior mini-thoracotomy. This surgical position is easily maintained for neonates in either the intensive care unit or in the operating room. Furthermore, this approach provides positional convenience for transition to sternotomy in emergency cases.

Patent ductus arteriosus closure with minimal invasive anterior thoracotomy is primarily derived from the technique published by Coles et al in 1963 for main pulmonary artery banding. ^{Reference Coles, Gergely and Buttigliero5} However, there have been few studies that examine the use of this surgical approach for patent ductus arteriosus closure since then in the literature. Fouilloux et al published a study of more than 50 symptomatic preterm infants with anterior minimal invasive thoracotomy. Although, they reported one case with irreversible tearing of the main pulmonary artery, the overall research findings indicated that this surgical technique was safe and reliable. ^{Reference Fouilloux, Gran and Kreitmann6} In another study of 21 preterm infants, Wanert et al similarly argued that surgical patent ductus arteriosus closure using anterior mini-thoracotomy was an effective technique with experienced surgeons in very low-weight preterm babies. No deaths related to surgery were reported. ^{Reference Wanert, Louali, Ovaert and Fouilloux7}

In almost five decades of treating preterm newborns for the closure of patent ductus arteriosus, the conventional surgery is lateral thoracotomy. ^{Reference Verhaegh, Accord and Kooi8} Direct visualisation and control of the ductus minimise potential risks. However, lung injury and potential long-term spinal and chest wall deformities are also well-recognised with this surgical approach. ^{Reference Bal, Elshershari, Celiker and Celiker9} In a study that compared posterolateral thoracotomy and median sternotomy approaches for patent ductus arteriosus closure in preterm neonates, Verhaegh et al found that the postoperative pulmonary complication rate was significantly lower in the median sternotomy patient group. ^{Reference Verhaegh, Accord and Kooi8} These findings indicate that surgical techniques involving no touching or less traction of lung tissue is significantly valuable.

The gentle traction of lung tissue and the ribs is surgically vital in preterm newborns. In the lateral thoracotomy approach, the spreading of the ribs may contribute to postoperative ventilator dependence. Left lung compression during ligation may also cause intrapulmonary haemorrhage and atelectasis. ^{Reference Raval, Laughon, Bose and Phillips10} In the anterior mini-thoracotomy approach, the incision is closer to the patent ductus arteriosus and therefore only the apex of the left lung is gently retracted, so the vulnerability of the lung tissue is less compared to other surgical techniques.

The two approaches to patent ductus arteriosus ligation include the conventional transpleural or the extrapleural approach. The transpleural approach may be complicated by intraoperative bleeding, pneumothorax, left vocal cord paralysis, lymphatic leak, and injury to the left phrenic nerve. ^{Reference Demirturk, Guvener, Coskun and Tunel11} Even if premature infants do not have a surgery, they can experience a variety of complications. And the potential for complications to occur significantly increases after any surgery. In our study we focussed only on complications directly attributable to the patent ductus arteriosus operation. In our cohort, we had one patient with chylothorax and chylomediastinum on postoperative day 26. We did not routinely screen our patients by diaphragmatic scopy and broncoscopy to evaluate the functions of recurrent laryngeal nerve and phrenic nerve unless we had detected prolonged intubation or hoarseness with unknown reason. Fortunately, none of the patients had left vocal cord or diaphragmatic paralysis or paresis. This is probably due to the way that this approach provides easy surgical exposure of the left phrenic nerve and the recurrent laryngeal nerve is untouched during the patent ductus arteriosus dissection. It should also be noted that dissection of the friable patent ductus arteriosus is extremely hazardous. Therefore, using a metallic vascular clip allows for limited dissection and safe occlusion. By comparison, it has not been necessary to insert a chest tube for drainage in any of our patients with our transpleural approach, which may have improved patient comfort during the postoperative period. We have evacuated the air with a suction catheter, one end of which is attached to the underwater drainage system while simultaneously inflating the lungs before ligation of the last skin suture. The extrapleural approach has better surgical exposure and involves less surgical dissection, which results in less risk of surgical complications and haemorrhage. ^{Reference Demirturk, Guvener, Coskun and Tunel11}

The main alternatives to conventional surgery for patent ductus arteriosus closure involve video-assisted thoracoscopy and percutaneous procedures. ^{Reference Garcia and Lukish12} While there are some potential advantages to using these techniques, vascular access and catheter manipulation during patent ductus arteriosus device closure in preterm infants can be particularly problematic for the percutaneous approach. ^{Reference Bansal, Prabhu, Ware and Shivapuje13} Therefore, conventional surgery is generally preferred over these alternative options. ^{Reference Stankowski, Aboul-Hassan and Seifi-Zinab14}

Most of our patients (82%) have been referred from other health centers to our hospital for patent ductus arteriosus surgery and have then been transferred back just after surgery. Transferal between two health centers can adversely affect postoperative outcomes for these high-risk infant patients, including the risk of thermoregulatory instability, loss of intravenous lines, malfunction and accidental discontinuity of monitoring and improper ventilation. ^{Reference Jennings, Innes, Wirth and Askew15} Fortunately, we have not experienced any problems due to these patient transfers.

In three patients (3%), we had to make median sternotomy because of the intraoperative massive bleeding of patent ductus arteriosus. Although we dissected the patent ductus arteriosus gently, some patent ductus arteriosus tissues were more fragile. When we were dissecting the patent ductus arteriosus or replacing the clip, unfortunately the patent ductus arteriosus was ruptured. We compressed over the patent ductus arteriosus with a sponge and immediately made median sternotomy to control the bleeding. We preferred the median sternotomy by reason of supine position of patients and with its advantage of wide and comfortable exposure of patent ductus arteriosus, heart, pulmonary artery, and aorta. The bleeding was controlled in all cases. All patients were survived after this complication.

Postoperative management of patent ductus arteriosus closure in preterm infants is a challenging problem. It requires us to be more cautious about potential problems in numerous organ systems. Indeed a few studies recorded hospital mortality rates up to 30%. ^{Reference Raval, Laughon, Bose and Phillips10–Reference Stankowski, Aboul-Hassan and Fritzsche16} We have recorded mortality rates that are higher than most other prior studies, ^{Reference Verhaegh, Accord and Kooi8,Reference Kang, Samsudin, Kuruvilla, Dhelaria, Kent and Kelsall19–Reference Lehenbauer, Fraser and Crawford22} (Table 4) mainly because our study involves all premature infants with patent ductus arteriosus, including babies who have severe morbidities. These mortality rates are not usually related to surgical or underlying cardiovascular pathology, but due to complications associated with prematurity. ^{Reference Hines, Raines and Payne17} Only one of our mortality cases was due to surgical complications. This particular patient weighed only 750 g and died in the operating room due to sudden cardiac arrest after clipping the patent ductus arteriosus. The remaining 17 mortality cases died within a year of surgery, mostly due to prematurity complications and infection.

Table 4.

Mortality rates of some studies in literature about surgical PDA ligation in low birth weight infants

GA: Gestational age

Our study has several limitations worth noting. Its retrospective nature and relatively small sample size limit the conclusions that may be derived. We did not attempt to compare the results of surgical ligation to medical management or other surgical approaches. Therefore, we cannot make claims about the superiority of one approach over another. Additionally, we focussed on early and mid-term morbidity and mortality in this study and did not assess patients for long-term outcomes. In terms of mid-term outcomes, the survival of our delicate patients is rarely related to the patent ductus arteriosus ligation operation itself. It is mostly related to prematurity complications in the mid- and long-term. Our intraoperative and short-term postoperative outcomes better demonstrate the success of our surgical technique for patent ductus arteriosus closure in preterm infants.

We conclude that patent ductus arteriosus ligation by anterior mini thoracotomy is a safe procedure with a low risk of surgical mortality and morbidity. Prospective randomised studies to compare anterior mini-thoracotomy to more traditional lateral thoracotomy are necessary to be conclusive on which surgical approach is most effective and safe.