Histopathological effect of balloon dilation in a live rabbit: Implications for the pediatric airway

Serial histological changes in the cartilaginous eustachian tube in the rat following balloon dilation

Although balloon dilation has shown promising results in the treatment of dilatory Eustachian tube (ET) dysfunction, the histological effects of ET balloon dilation (ETBD) is unknown because histological examination of the whole human cartilaginous ET is impossible. Animal studies are needed to elucidate the effect of ETBD so we evaluated the histological changes after ETBD in a rat model. The left ET of 20 Wistar rats was dilated with a balloon catheter and the right ET was used as a control. Five rats were sacrificed immediately after ETBD, at 1, 4 and 12 weeks after the procedure for histological examination. The epithelial cells, presence of epithelial hyperplasia, and the proportion of the goblet cells in the epithelium; the vascular structures and dimensions of the submucosa; and presence of cartilage fracture and the area of the ET lumen were evaluated and compared between the groups. Desquamation of nearly all epithelial cells and the fracture of tubal cartilages were observed immediately after ETBD. At 1-week post-ETBD, the ciliated epithelial cells started to recover with epithelial hyperplasia. The goblet cells recovered by 4 weeks post-ETBD and epithelial hyperplasia decreased but was still present at 12 weeks post-ETBD. The depth of the submucosa increased and neovascularization in this region was observed at 1-week post-ETBD and persisted up to 12 weeks post-ETBD. The lumen of the cartilaginous ET increased immediately after ETBD but decreased at 1-week post-ETBD. The cartilaginous ET lumen recovered to the normal value at 4 weeks post-ETBD. This study is the first to describe the serial histological changes to the cartilaginous ET after ETBD and helps our understanding of the histological changes that occur after an ETBD intervention for intractable ET dysfunction.

Establishing an Endoscopic Chronic Subglottic Stenosis Rabbit Model

OBJECTIVES/HYPOTHESIS

To develop a reproducible and consistent chronic subglottic stenosis (SGS) in an endoscopic animal model.

STUDY DESIGN

Prospective study.

METHODS

We conducted a prospective study using New Zealand white rabbits. Chronic SGS was induced endoscopically by Bugbee electrocautery to 50% to 75% of the subglottic area's circumference, followed by 4-hour endotracheal intubation. The rabbit airways were endoscopically assessed and sized with uncuffed endotracheal tubes (ETTs) before the injury, during follow-up, and at the endpoints. There were four endpoints: 2, 4, 6, and 8 weeks post SGS induction. Animals were humanely euthanized for histopathological examination of the subglottic injury site and microscopic measurement of the cricoid lumen.

RESULTS

Twenty-two rabbits reached the endpoints, and 18 rabbits developed chronic SGS. ETT size significantly decreased by 0.5 from preinjury to the endpoint in all groups, P < .001. Control median cricoid lumen measurements were 20.48 mm² , the median cricoid lumen measurement for the 2 weeks endpoint was 14.3 mm² , 4 weeks 11.69 mm² , 6 weeks 16.03 mm² , and 8 weeks endpoint median was 16.33 mm² . Histopathological examination showed chronic scar tissue and new cartilage formation at the cricoid level, mainly at the posterior subglottic injury site starting from 4 weeks postinjury. Collagen staining revealed substantial amounts of organized collagen and different collagen orientation starting 4 weeks postinjury lasting until 8 weeks postinjury.

CONCLUSION

We developed an animal model to study chronic SGS. This model will be utilized to compare different endoscopic treatment interventions in acute SGS versus chronic SGS and further define the molecular basis of SGS.

LEVEL OF EVIDENCE

NA Laryngoscope, 2021.

Randomized Controlled Trial of Balloon Dilation in Treatment of Subglottic Stenosis With a Rabbit Model

OBJECTIVES

Identify the effects of balloon dilation duration and topical ciprofloxacin-dexamethasone application in treatment of subglottic stenosis.

STUDY DESIGN

Randomized controlled trial.

SETTING

Animal research facility.

SUBJECTS AND METHODS

Forty-four rabbits underwent subglottic injury in an Institutional Animal Care and Use Committee-approved study. One week after injury, the subglottis of each rabbit was measured and treated with endoscopic balloon dilation for 2 rounds of short duration (SBD; 3 seconds), long duration (LBD; 30 seconds), or LBD with topical ciprofloxacin-dexamethasone application (LBD+C). The subglottis of each rabbit was remeasured at the study endpoint: 1 month postdilation or following development of life-threatening respiratory distress.

RESULTS

Of 44 rabbits, 35 (80%) survived to endoscopic balloon dilation, with 21 rabbits developing a grade III Cotton-Myer stenosis. Prior to dilation, there was no difference in stenosis rates among groups (all subjects, P = .99; grade III stenosis only, P = .52). Among grade III subjects, improvement in stenosis after dilation was -1% (SD, 21%) for SBD, 27% (SD, 38%) for LBD, and 58% (SD, 29%) for LBD+C (P = .01). Early euthanasia/death rates among grade III subjects were 85% for SBD, 63% for LBD, and 17% for LBD+C (P = .03). Time to early euthanasia/death was 5.0 days for the SBD group and 8.4 days for the LBD group (P = .04).

CONCLUSION

SBD was inferior to LBD or LBD+C in multiple metrics. LBD+C offered significant improvements in stenosis size and mortality over the SBD group and had the lowest rate of early mortality. Further research is needed to identify optimal balloon dilation treatment duration.

The mechanism of balloon Eustachian tuboplasty: a biomechanical study

Obstructive Eustachian tube dysfunction (OETD) is a common condition resulting from inadequate opening of the Eustachian tube (ET). A new surgical treatment involves high-pressure inflation of a balloon within the ET, with the aim of dilating the soft tissue structure. However, the mechanical effects of this intervention have not been established, nor the impact of changing device size or other technical parameters. A novel experimental technique allowed quantification of plastic and elastic tissue deformation in model materials and then human cadaver ETs during balloon dilation, based on the measured balloon inflation pressure-volume relationship. Plastic tissue deformation was found to be greater using larger balloons and deeper device insertion, but increasing the inflation pressure had a more limited effect, with most deformation occurring well below the clinically used pressures. Histological assessment of ET tissue suggested that mucosal tearing and cartilage cracking were in part responsible for the mechanical changes. Balloon dilation of the ET has huge potential if found to be clinically effective, but currently there is a need to understand and develop the technique further. The novel methods employed in this study will be valuable in future laboratory and in vivo studies of ET balloon dilation. Pressures are reported in Bar as this unit is used for medical balloon dilation procedures in clinical practice. 1 Bar = 100,000 Pa.

Graphical abstract caption

Development of a survival animal model for subglottic stenosis

OBJECTIVE

To develop a reproducible survival animal model for subglottic stenosis.

STUDY DESIGN

Prospective study.

METHODS

We evaluated five methods of inducing airway injury in 30 New Zealand white rabbits to produce a subglottic stenosis model. Experimental groups comprised: group 1 (n = 5), which underwent 4-hour intubation; group 2 (n = 5), which underwent induced subglottic injury with a nylon brush; group 3 (n = 10), which underwent subglottic injury with a nylon brush, followed by 4-hour intubation; group 4 (n = 5), which underwent subglottic injury with Bugbee cautery in 50% of the subglottic circumference, followed by 4-hour intubation; and group 5 (n = 5), which underwent subglottic injury with Bugbee cautery in 75% of the subglottic circumference, followed by 4-hour intubation. Five animals were used as controls. Endoscopy of the airway and sacrifice of animals were planned at an interval of 14 days postinjury. Histologic measurements were analyzed.

RESULTS

No animals in groups 1 or 2 developed stenosis. In group 3, 50% of animals developed symptomatic grade 3 subglottic and tracheal stenosis, necessitating early endoscopy and sacrifice in three animals. Four animals in group 4 developed grade 1 subglottic stenosis, and four in group 5 developed grade 2 subglottic stenosis. Histologic measurements of lumen areas within each of these two groups were similar; all animals survived the follow-up period.

CONCLUSION

We successfully developed a reproducible survival model for induced subglottic stenosis using a combination of cautery-induced subglottic injury followed by 4-hour intubation. This model lays the foundation for future studies that evaluate endoscopic interventions for the management of subglottic stenosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:989-994, 2019.

Rigid dilatation of pediatric laryngotracheal stenosis as an adequate alternative to balloon dilatation

INTRODUCTION

Endoscopic balloon dilation (EBD) is the mainstay of endoscopic therapy for laryngotracheal stenosis (LTS), although there is no evidence that it achieves better results than traditional rigid laryngeal dilators. Rigid bougie dilators are less expensive and easier to use, and confer the advantage of providing tactile information about the stenosis to the surgeon. We analyzed the outcome of endoscopic rigid bougie dilatation of LTS in a large series of children and compared it to the reported results of EBD in the same setting.

PATIENTS AND METHODS

All cases of pediatric LTS treated by endoscopic rigid dilatation in a tertiary referral center between 2006 and 2015 were retrospectively studied. They were divided into a primary dilatation group (PDG) and a post-reconstruction dilatation group (PRG). The PDG children had no history of reconstructive airway surgery, and dilatation was the major treatment approach. The PRG children underwent dilatations after airway reconstruction surgery as part of routine postoperative management. A successful primary outcome was defined as improvement of dyspnea and achievement of a functional airway without reconstructive laryngotracheal surgery or need for a tracheostomy at final follow-up.

RESULTS

Sixty-two children (68 cases, mean age 5.1 years, range 0.7-17.2) underwent 156 endoscopic rigid dilatations. Successful outcome was achieved in 48 cases (70.6%), 73.0% in the PDG and 67.7% in the PRG. There were no procedure-related adverse events.

CONCLUSIONS

Endoscopic rigid dilatation is a relatively inexpensive and efficacious tool in endoscopic management of pediatric LTS. Its success rates are in the same range as those of EBD.

Impact of balloon laryngoplasty on management of acute subglottic stenosis

PURPOSE

To assess the impact of balloon laryngoplasty on clinical and surgical outcomes in pediatric patients with acute subglottic stenosis.

METHODS

Two case series were included and compared. The first group included patients treated initially either with tracheostomy (if severe symptoms) or with close follow-up (if mild symptoms). Those children underwent re-evaluation and specific treatment of their stenosis with laser incisions or open surgeries some weeks later. The other group included children treated initially with balloon laryngoplasty, reflecting a shift in surgical practice after 2009. Data as success of the procedure, mean hospital stay, mean pediatric intensive care unit (PICU) stay, post-procedure fever, need of antibiotics, procedure-related complications, and deaths were assessed and compared between both cohorts.

RESULTS

The sample comprised 38 pediatric patients aged 0-5 years. Fifteen children were treated before 2009, of who 10 (66.7%) required tracheostomy soon after the diagnosis. Ultimately, 13 (86.6%) underwent laryngotracheal reconstruction. Twenty-three children were treated after 2009 and the success rate in these patients treated primarily with balloon laryngoplasty was 82.6%. Of these, only 3 (13%) required tracheostomy and 1 (4.3%) required further open laryngotracheal reconstruction. Patients treated by balloon laryngoplasty underwent fewer procedures under general anesthesia and had a lower burden of treatment-related morbidity, as denoted by shorter PICU stay, less antibiotic use, earlier postoperative resumption of oral feeding, and a lower incidence of postoperative complications and fever.

CONCLUSION

When used for management of acute laryngeal stenosis, balloon laryngoplasty is associated with a high success rate, presenting lower morbidity than open surgery.

Analysis of Reported Balloon Malfunctions and Proposed Rescue Strategy for Malfunction during Airway Dilation

Objective The rate of balloon dilator failure is unknown, and a rescue strategy for device malfunction has not been established. The purposes of this investigation were to determine the approximate number of balloon failures in the gastrointestinal tract and airway, evaluate the parameters required to rupture balloon dilators, and develop a rescue strategy to efficiently reestablish airway patency. Study Design Retrospective cohort and basic medical research. Setting Academic tertiary care medical center. Subjects and Methods The Manufacturer and User Facility Device Experience database was queried for adverse events associated with tracheal and esophageal dilators between January 1, 2014, and January 1, 2017. A bench-top model of airway stenosis was developed, and optimal conditions for the safe removal of a malfunctioning dilator were assessed (2, 4, 6 atm). Results There were 420 reported balloon malfunctions, including 104 cases with deflation/removal issues. The bench-top model determined that device rupture allowing for immediate removal occurs with needle puncture at balloon pressures ≥8 atm. Balloons inflated to 6 atm required a median of 17.5 seconds (range, 0-55.3) for removal, in comparison with 30.2 seconds (range, 7.1-87.5) at 2 atm ( P > .05). Conclusion Balloon dilator malfunction is a significant problem that practitioners must be prepared for. Pressure ≥8 atm (~33% overinflation) is required to consistently cause complete balloon dilator rupture via needle puncture. While counterintuitive, increasing the inflation pressure of a malfunctioning balloon (8-10 atm) may expedite rupture and safe removal. A rescue strategy for balloon malfunction is proposed.

Reproducing severe acute subglottic stenosis in a rabbit model

OBJECTIVES

The objectives of this study were to develop an animal model with consistent, severe subglottic stenosis (SGS), and to develop the timeline needed for intervention to limit rabbit mortality.

METHODS

Subglottic stenosis was created endoscopically using either a nylon or polypropylene brush in sixteen New Zealand White rabbits. The subglottic cross-sectional area was measured endoscopically using a right-angled probe and an open source image analysis software The cross-sectional areas of the stenotic and native airways were compared to calculate the subglottic stenosis percentage and Myer-Cotton grade classification.

RESULTS

The average diameter of the native subglottis was 4.7 mm (SD 0.4). The mean subglottic stenosis percentage was 73% (SD 32) for all rabbits. The three rabbits injured with the nylon brush had 30, 52, and 76% stenosis. Nine of the 12 surviving rabbits (75%) injured with the polypropylene brush had a >86% subglottic stenosis. Four rabbits in the polypropylene brush cohort died from procedural complications.

CONCLUSION

This study demonstrates a reliable model using a polypropylene brush to create severe acute subglottic stenosis. Cartilage exposure after creating the injury was associated with more severe stenosis. Mortality rate may have been reduced if endoscopic balloon dilation was performed electively seven days after injury, rather than emergently nine days after injury.

LEVEL OF EVIDENCE

4.

Effects of supramaximal balloon dilatation pressures on adult cricoid and tracheal cartilage: A cadaveric study

OBJECTIVES/HYPOTHESIS

Cricoid fracture is a serious concern for balloon dilatation in airway stenosis. Furthermore, there are no studies examining tracheal rupture in balloon dilatation of stenotic segments. The aim of this study was to evaluate the effect of supramaximal pressures of balloons on the cricoid and tracheal rings.

STUDY DESIGN

Prospective cadaveric study.

METHODS

Seven cadaveric laryngotracheal complexes of normal adults with intact cricothyroid membranes were acquired. Noncompliant vascular angioplasty balloons (BARD-VIDA) were used for dilatation. The subglottis and trachea were subjected to supramaximal dilatation pressures graduated to nominal burst pressure (NBP) and, if necessary, rated burst pressure (RBP). Larger-diameter balloons, starting from 18 mm size to 24 mm, were used. Dilatations were maintained for 3 minutes.

RESULTS

The cricoid ring was disrupted by larger-diameter balloons (22 mm and 24 mm) even at lower pressures (less than NBP) in six cases. Tracheal cartilages were very distensible, and external examination after supramaximal dilatation (24 mm close to RBP) revealed no obvious cartilage fractures or trachealis tears. Histopathological examination revealed sloughing of mucosa in the areas corresponding to balloon placement, but no microfractures or disruption of the perichondrium of tracheal ring cartilages.

CONCLUSIONS

These results indicate that the cricoid is vulnerable to injury from larger balloons even at lower dilatation pressures. The tracheal cartilages and the membranous wall of the trachea remained resilient to supramaximal dilatation and larger balloons.

LEVEL OF EVIDENCE

NA. Laryngoscope, 128:1304-1309, 2018.

Safe balloon sizing for endoscopic dilatation of subglottic stenosis in children

Objectives:

To describe our experience and provide guidelines for maximum safe balloon sizes according to age in children undergoing balloon dilatation.

Method:

A retrospective review was conducted of children undergoing balloon dilatation for subglottic stenosis in a paediatric tertiary unit between May 2006 and February 2016.

Results:

A total of 166 patients underwent balloon dilatation. Mean ( ± standard deviation) patient age was 4.5 ± 3.99 years. The median balloon size was 8 mm, the median balloon inflation pressure was 10 atm, and the mean balloon inflation time was 65.1 ± 18.6 seconds. No significant unexpected events occurred. The Pearson correlation co-efficient for the relationship between patient age and balloon size was 0.85 (p = 0.001), suggesting a strongly positive correlation.

Conclusion:

This study demonstrated that balloon dilatation is a safe procedure for airway stenosis. The results suggest using a balloon diameter that is equal to the outer diameter of the age-appropriate endotracheal tube +1 mm for the larynx and subglottis and +2 mm for the trachea.