Management and outcome:
The management of LPA sling is beyond the scope of the review but is primarily to determine the exact relationship between the tracheobronchial abnormalities and the presenting symptoms and to delineate the extent of airway involvement and stenosis as this significantly influences the outcome. Assisted ventilation or cardiac arrest prior to surgery, associated  genetic abnormalities and major cardiac defects are known risk factors which adversely affect the outcome. The most challenging cases which require assisted ventilation,the pressure control ventilation using inspiratory plateau pressure rather than peak pressure is essential as 30 to 50% of the airway pressure is lost and dissipated through the trachea obstruction. This is similar to the permissive hypercarbia strategy originally described  by Darioli and Perret for acute severe asthma.46 However; in contrast to asthma, long inspiratory times of 0.8 to 1 second allow better ventilation as the obstruction is during the inspiratory phase.47Usually, lower respiratory rates prevent air trapping and high frequency oscillation is of no benefit. In extreme cases, an extracorporeal membrane oxygenator (ECMO) is required.
Correction of tracheal stenosis is usually under cardiopulmonary bypass especially if there is long segment tracheal stenosis requiring tracheal surgery or tracheoplasty. The left pulmonary artery is re-implanted and any major congenital heart lesions are usually repaired at the same time.27,28,48-51
Over the years, there have been many different surgical procedures to treat tracheal stenosis including end-to-end anastomosis for short segment stenosis, patch tracheoplasty (with autologous pericardium, tracheal autograft, aortic homograft) and more recently the slide tracheoplasty. The slide tracheoplasty technique is performed by tracheal division at the midpoint of stenosis, longitudinal incisions on the opposite side of proximal and distal tracheal segments and sliding oblique anastomosis of the segment.27,28,48,49 Success of this procedure depends on freeing and mobilising the trachea which will then be foreshortened with the slide but increase its diameter without the risk of ischaemia. This innovative technique has shown impressive results all round the world in specialised airway centres with over 70% survival.29-32,51-59 Length of ICU stay is generally significantly shorter for slide tracheoplasty with less complications.51,56-59 Average age of surgery is around six months of age which is similar to the time of presentation.
Typically, patients are ventilated for a few days to allow the tracheal sutures to heal and then the patient may require multiple balloon dilations in the ensuing 12 to 24 months at increasingly less frequent intervals. Following slide tracheoplasty, the trachea usually grows with age with no limitations on exercise later in childhood or adulthood.60 At the more complex end of the spectrum there may be associated tracheobronchial malacia which may be approached by a number of ways including long-term ventilation or airway stenting, more recently with biodegradable stents.7,40,61Untreated tracheal stenosis especially with complete rings may progress and require intervention, although mild cases may be managed without tracheal surgery. However this concept remains as a controversial subject in many centres.34,62-65
Reimplanted left pulmonary artery may get stenosis in the future. Ventilation-perfusion scan or cardiac MRI will help to quantify the differential flow to each lung when there is a stenosis of the re-anastomosed pulmonary artery.. Catheter based interventions in the form of ballooning or stenting of the LPA might be required in cases of significant LPA stenosis.66
Survival following isolated left pulmonary artery repair (type 1)  is usually excellent, approximately 100%.67,68 In most large case series there has been significant improvement over the last three decades with  improving surgical techniques. Even at the severe end of the spectrum, LPA sling occurs in association with long segment tracheal stenosis; survival figures vary from 50 to above 90%.34,69 There are even reports of reasonable survival  for tracheal stenosis following slide tracheoplasty with a single lung.61,70 Improved survival over the last decade also been due to the wider adoption of complex airway services and multidisciplinary teams which evaluate not only the heart and the airway but focus on other issues such as feeding, swallowing and neurodevelopment.71 Management of this rare tracheobronchial vascular abnormality is better achieved in large specialised centres with highly skilled staff and availability of advanced diagnostic equipment.71 Being a rare tracheobronchial vascular abnormality, its management experience with a low volume centre is expected to be less,hence it is advisable to perform the management in large specialised centres where highly skilled staff and advanced diagnostic equipments are available.
Table 1  Classification of LPA sling according to Wells.
Aberrant left pulmonary artery sling with the following features: