Subglottic Stenosis
Although congenital subglottic stenosis is rare, acquired subglottic
stenosis is common in neonates with BPD. The cricoid is the narrowest
portion of the pediatric airway; as a result the cricoid is the most
likely area to be damaged in neonates requiring intubation.(44) Multiple
factors predispose children to developing subglottic stenosis including
duration of intubation, multiple intubation attempts, traumatic
intubation, nasal vs oral intubation, endotracheal tube composition, and
inadequate sedation.(45-48) However, the most important factor is the
relative size of the endotracheal tube to the patient’s airway.(46) The
endotracheal tube exerts pressure of the airway mucosa that can exceed
capillary filling pressure, particularly with cuffed endotracheal tubes.
(49, 50) Within two hours, pathologic changes of the airway mucosa
related to intubation can occur, and the alterations of the airway
mucosa progress with longer periods of intubation.(51, 52) Damage to the
airway related to endotracheal intubation can eventually lead to tissue
necrosis and scar formation that manifests as subglottic stenosis
Post-intubation subglottic stenosis develops in 0.9-8.3% of intubated
neonates; however, because of the small airway size, prolonged
intubation, and multiple intubation attempts, the risk of subglottic
stenosis in BPD is likely higher than other neonatal populations. (48,
53) As with TBM, the diagnosis of subglottic stenosis depends on imaging
techniques that expose neonates to the ionizing radiation and/or direct
visualization with bronchoscopy; thus, the true incidence of subglottic
stenosis in BPD is unknown. Subglottic stenosis can be suspected based
on airway plain films or computed tomography; (54, 55) however,
definitive diagnosis is made by bronchoscopy. Subglottic stenosis is
classified using the Myer-Cotton grading scale, which determines the
largest endotracheal tube that permits an air leak at 20 cm
H2O. The severity of subglottic stenosis is defined as
grade 1 (<50% narrowed), grade 2 (51-70% narrowed), grade 3
(71-99%narrowed), and grade 4 (no detectable lumen) (Fig.3B-E).(56)
As the severity of subglottic narrowing increases, airway resistance and
respiratory work increases exponentially. Clearly, the extent of the
stenosis is the primary driver, but the length of the stenotic segment
and the location of the stenosis in relationship with the glottis also
impacts airway resistance. (57, 58) The narrowing and increased airway
resistance most commonly manifests with biphasic stridor and increased
respiratory effort. Indeed, neonates with subglottic stenosis may not
tolerate extubation and are at high risk of undergoing tracheotomy. (20,
59)
Management of subglottic stenosis in neonates with BPD should focus on
prevention. Recent efforts have increased the use of nasal CPAP at birth
rather than intubation to minimize the risk of the development of
BPD.(60, 61) If neonates are adequately supported non-invasively,
acquired subglottic stenosis does not develop. Non-invasive positive
airway pressure can also be utilized to minimize the risk of extubation
failure, thereby reducing the risk of airway trauma related to multiple
intubations.(62) In the event that endotracheal intubation is necessary,
an endotracheal tube that leaks at less than 20-25 cm
H2O minimizes the risk of developing subglottic
injury;(63) unfortunately, this may not be feasible to adequately
support gas exchange and respiratory comfort in patients with
particularly severe lung disease. For patients who require prolonged
intubation, adequate sedation that minimizes agitation may also limit
the development of subglottic stenosis. (47)
If a neonate with BPD does develop subglottic stenosis treatment options
include non-operative measures, endoscopic intervention, open airway
surgery, and tracheotomy. Non-operative treatments include downsizing to
a smaller endotracheal tube that permits an air-leak at 20-25 cm H20
combined with topical steroid and antibiotic drops delivered via the
endotracheal tube. An oral endotracheal tube can be replaced with an
nasal tube to minimize mucosal trauma related to movement of the tube
along the axis of the airway.(44) Even if non-operative measures do not
prevent the need for surgical management, reduction of airway edema and
inflammation may aid operative intervention.
For patients with grade 1 or grade 2 subglottic stenosis, balloon
dilation is the mainstay of endoscopic intervention. Balloon dilation is
a minimally invasive technique that involves inflating a high pressure,
non-compliant airway balloon in the narrowed segment of the airway and
is generally safe and well-tolerated; however, multiple dilations are
often needed for a successful outcome. (64, 65) While endoscopic balloon
dilation is successful at avoiding tracheotomy in a majority of
pediatric patients with mild subglottic stenosis, balloon dilation is
frequently inadequate for more severe stenoses.(64-66) Infants that are
born premature or have multiple medical comorbidities appear to be at
increased risk of failed endoscopic balloon dilation and are more likely
to need invasive surgical interventions.(66)
Surgical options available for the management of subglottic stenosis in
neonates with BPD include cricoid split, laryngotracheal reconstruction
with cartilage grafting, and tracheotomy. Anterior cricoid split was
first described in 1980 for aiding extubation in premature infants with
isolated subglottic stenosis. The operation involves a small neck
incision over the cricoid and a vertical incision in the anterior airway
from the lower thyroid cartilage to the upper two tracheal rings. The
endotracheal tube is left in place, and the airway is allowed to heal by
secondary intention. In highly selective patients, anterior cricoid
split is successful in facilitating extubation.(67) In more severe
cases, modifications to this technique include the placement of a
cartilage graft using thyroid ala or costal cartilage to close the
airway and a posterior cricoid split with or without a posterior
cartilage graft.(68, 69) In the event that a cartilage graft is used,
the operation is referred to as laryngotracheal reconstruction, which is
highly successful for appropriately selected patients, even with severe
subglottic stenosis.(69, 70) For infants that are likely to need
prolonged mechanical ventilation for parenchymal lung disease or those
who are not candidates for airway reconstruction, tracheotomy can be
pursued to bypass the stenotic segment.