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: