The 'knee' pattern in spirometry flow-volume curves in children: Does it relate to tracheomalacia?

BACKGROUND: There is little data on patterns of spirometry curves in children with tracheomalacia but convex inflection on flow-volume curves (identified as the 'knee') is thought to represent tracheomalacia. OBJECTIVES: To determine (a) the prevalence of tracheomalacia in children with the 'knee' pattern on spirometry, and (b) whether spirometry parameters and visual characteristics of the 'knee' can identify presence/absence or severity of tracheomalacia. PATIENTS/METHODS: We reviewed the spirometry undertaken at Queensland Children's Hospital between 2016 and 2019 and retrieved spirometry with the 'knee' pattern in the flow-volume curves. Flexible bronchoscopy videos of these children were reviewed for tracheomalacia diagnosis and severity in a blinded manner. We also evaluated several 'knee' characteristics (onset of inflection, angle of inflection, a scoop before plateau, plateau progression), spirometry parameters and tracheomalacia severity. RESULTS: Of the 78 children with the 'knee', 51 (65.4%) had tracheomalacia. Spirometry values were significantly lower in those with tracheomalacia, compared to those without (predicted FEV1 = 86.1% vs 99.9%, FVC = 95.1% vs 104%, FEF25-75% = 68.6% vs 89.6%, all p < 0.02). A scoop before plateau was significantly associated with tracheomalacia (66.7% vs 40.7%, p = 0.03). There was no significant difference in spirometry parameters or the 'knee' characteristics between children with mild versus moderate-to-severe tracheomalacia. CONCLUSION: Most but not all children with the 'knee' pattern have flexible bronchoscopy-defined tracheomalacia. Those with tracheomalacia had lower spirometry values and the presence of a scoop before plateau was the most characteristic feature. A prospective longitudinal study is required to determine the diagnostic value of spirometry flow-volume curve characteristics in children.

Management of bronchomalacia in infants post-cardiac surgery using synchronized nasal DuoPAP: A novel technology.

Background: Tracheo-bronchomalacia (TBM) is the weakness in the structural integrity of the cartilaginous ring and arch. It may occur in isolation with prematurity or secondarily in association with various congenital anomalies. Bronchomalacia is more commonly associated with congenital heart diseases. The conventional treatment options include positive pressure ventilation with or without tracheostomy, surgical correction of external compression and airway stenting. Aim: To use "synchronized" nasal Dual positive airway pressure (DuoPAP), a non-invasive mode of ventilation as an alternative treatment option for bronchomalacia to avoid complications associated with conventional treatment modalities. Study Design: Prospective observational study conducted in Army Hospital Research and Referral from Jul 2019 to Dec 2020. Material and Methods: We diagnosed seven cases of TBM post-cardiac surgery at our institute, incidence of 4.2%. Four infants were diagnosed with left sided bronchomalacia, 2 were diagnosed with right sided bronchomalacia and one with tracheomalacia. Those infants were managed by "synchronized" nasal DuoPAP, a first in ventilation technology by Fabian Therapy Evolution ventilator (Acutronic, Switzerland). Results: All seven infants showed significant improvement with synchronized nasal DuoPAP both clinically as well as radiologically. None of the infant required tracheostomy and discharged to home successfully. Conclusion: The synchronized nasal DuoPAP is a low cost and effective treatment option for infants with TBM. It could be attributed to synchronization of the breaths leading to better tolerance and compliance in paediatric age group.

Thoracoscopic posterior tracheopexy during primary esophageal atresia repair ameliorate tracheomalacia in neonates: a single-center retrospective comparative cohort study.

BACKGROUND: Esophageal atresia (EA) is often associated with tracheomalacia (TM). The severity of TM symptoms varies widely, with serious cases requiring prolonged respiratory support and surgical treatment. Although we performed thoracoscopic posterior tracheopexy (TPT) during primary EA repair to prevent or reduce the symptoms of TM, few studies have investigated the safety and effectiveness of TPT during primary EA repair. Therefore, this study aimed to evaluate the safety and efficacy of TPT in neonates. METHODS: We retrospectively reviewed the records of all patients diagnosed with TM who underwent primary thoracoscopic EA repair between 2013 and 2020 at the Nagoya University Hospital. Patients were divided into two groups: TPT (TPT group) and without TPT (control group). TPT has been performed in all patients with EA complicated by TM since 2020. We compared patient backgrounds, surgical outcomes, postoperative complications, and treatment efficacy. RESULTS: Of the 22 patients reviewed, eight were in the TPT group and 14 were in the control group. There were no statistically significant differences in the surgical outcomes between the groups (operation time: p = 0.31; blood loss: p = 0.83; time to extubation: p = 0.30; time to start enteral feeding: p = 0.19; time to start oral feeding: p = 0.43). Conversion to open thoracotomy was not performed in any case. The median operative time required for posterior tracheopexy was 10 (8-15) min. There were no statistically significant differences in postoperative complications between the groups (chylothorax: p = 0.36; leakage: p = 1.00; stricture: p = 0.53). The respiratory dependence rate 30 days postoperative (2 [25%] vs. 11 [79%], p = 0.03) and the ratio of the lateral and anterior-posterior diameter of the trachea (LAR) were significantly lower in the TPT group (1.83 [1.66-2.78] vs. 3.59 [1.80-7.70], p = 0.01). CONCLUSIONS: TPT during primary EA repair for treatment of TM significantly lowered respiratory dependence rate at 30 days postoperative without increasing the risk of postoperative complications. This study suggested that TPT could improve TM associated with EA.

Is secondary tracheomalacia associated with airway inflammation and infection?

BACKGROUND: Recurrent lower respiratory tract infections are among the most prevalent symptoms in secondary tracheomalacia due to mediastinal vascular anomalies (MVAs). It is not known whether this condition could result in persistent lower respiratory tract inflammation and subclinical infection. METHODS: A retrospective study was performed on records of children with tracheomalacia due to MVAs and recurrent respiratory infections who underwent computed tomography scan, bronchoscopy, and bronchoalveolar lavage (BAL) as part of their clinical evaluation. RESULTS: Thirty-one children were included in the study: 21 with aberrant innominate artery, four with right aortic arch, one with double aortic arch, and five with aberrant innominate artery associated with right aortic arch. Cytological evaluation of bronchoalveolar lavage fluid showed increased neutrophil percentages and normal lymphocyte and eosinophil proportions. Microorganism growth was detected in 13 BAL samples, with a bacterial load ≥104 colony-forming units/mL in eight (25.8%) of them. Most isolates were positive for Haemophilus influenzae. Bronchiectasis was detected in four children, all with BAL culture positive for H. influenzae. Four patients underwent MVA surgical correction and 27 conservative management, i.e., respiratory physiotherapy in all and high-dose amoxicillin/clavulanic acid (40 mg/kg/day) for 2-4 weeks in those with significant bacterial growth. There was an excellent outcome in most of them. CONCLUSIONS: Neutrophilic alveolitis is detectable in secondary tracheomalacia but is associated with a clinically significant bacterial load only in a quarter of the patients. Caution should be used regarding inappropriate antibiotic prescriptions to avoid the emergence of resistance, whilst airway clearance maneuvers and infection preventive measures should be promoted.

Tracheomalacia after thyroidectomy for retrosternal goitres requiring sternotomy- a myth or reality?

INTRODUCTION: Tracheomalacia after thyroidectomy is not well understood. Reports on tracheomalacia are conflicting, with some suggesting a high rate and other large cohorts in which no tracheomalacia is reported. The aim of our study was to assess the incidence and factors associated with tracheomalacia after thyroidectomy in patients with retrosternal goitres requiring sternotomy at a high-volume tertiary care referral centre. METHODS: A longitudinal cohort study was conducted from January 2011 to December 2019. All adult patients who underwent thyroidectomy with sternotomy were included. Tracheomalacia was considered when tracheal rings were soft compared with other parts (proximal or distal) of the trachea and required either tracheostomy or resection with anastomosis. The decision to perform a tracheostomy or to administer continuous or bilevel positive airway pressure postoperatively was made depending on the degree of tracheomalacia. Logistic regression analysis was used to assess factors associated with tracheomalacia. RESULTS: We evaluated 40 patients who underwent thyroidectomy with sternotomy. The mean age of our cohort was 48.7 ± 11.3 years and the population was predominantly female (67.5%). One patient required tracheal resection with anastomosis, and two patients required tracheostomy. Multivariable logistic regression analysis did not reveal any patient- or thyroid-related factor significantly associated with the development of tracheomalacia in our cohort. CONCLUSIONS: The incidence of tracheomalacia after thyroidectomy with sternotomy appears to be very low. However, the occurrence of tracheomalacia after thyroidectomy in cases of large goitre is possible and hence worrisome.

Airway Clearance in Tracheomalacia.

Airway clearance is an essential part of airway maintenance to ensure the airway lumen is protected against particulate and infectious insults. The mechanisms involved in airway clearance include intrinsic structural and cellular components that can be impaired or inhibited through developmental defects and surgical interventions. Tracheomalacia is a developmental defect of the airway that can contribute to the mechanical failure to clear the airway. This chapter will review the mechanisms of airway clearance and the processes that can impair this vital process.

[Treatment of tracheo(broncho)malacia in children]. / Comment je traite la trachéo(broncho)malacie de l'enfant ?

Tracheomalacia (TM) is characterized by tracheal collapse due to an intrinsic anomaly resulting in a lack of rigidity of the cartilaginous rings and/or the posterior membrane during expiration, coughing or crying. It may also be secondary to external compression or acquired during endobronchial diseases. TM is commonly associated with other syndromes or airway abnormalities. Tracheomalacia can be localized or diffused and if the main bronchi are involved, the term of tracheobronchomalacia (TBM) is used. The most common symptoms include expiratory stridor, barking cough and recurrent respiratory tract infections. If tracheal weakness is severe, Acute Life Threating Events (ALTE) or Brief Resolved Unexplained Event (BRUE) can occur. While mild forms usually do not require any treatment, severe TBM may require medical and/or surgical management. Amongst several possible treatments, including tracheostomy, noninvasive ventilation and airway stenting, the pexy surgical approach (posterior, anterior tracheopexy or aortopexy) is currently the favoured option.

La trachéomalacie (TM) est caractérisée par un collapsus trachéal plus ou moins important durant l'expiration, lors des efforts de toux ou des pleurs. Elle peut être due à une anomalie intrinsèque, par manque de rigidité des anneaux cartilagineux et/ou de la membrane postérieure. Elle peut aussi avoir une origine extrinsèque, soit secondaire à une compression externe, soit acquise dans le cadre de pathologies endo-bronchiques. Elle peut enfin être associée à certains syndromes ou malformations des voies respiratoires. La TM peut être localisée ou généralisée, et si les bronches principales sont atteintes, on parlera de trachéobronchomalacie (TBM). Les symptômes les plus courants sont : un stridor expiratoire, une toux aboyante, et des infections respiratoires récurrentes. Dans les cas les plus sévères, des événements menaçant la vie de l'enfant (Acute Life-Threatening Event «ALTE¼ ou Brief Resolved Unexplained Event «BRUE¼) peuvent survenir. Alors que les formes légères ne requièrent généralement pas de traitement, la TBM sévère peut nécessiter une prise en charge médicale et/ou chirurgicale. Parmi les divers choix thérapeutiques, incluant notamment la trachéostomie, la ventilation non invasive et les stents trachéaux, l'approche chirurgicale par pexie (aortopexie, trachéopexie postérieure ou antérieure) est actuellement l'option favorite.

Reconstruction of the Mediastinum and Tracheopexy for Tracheomalacia in Straight Back Syndrome.

Tracheomalacia in straight back syndrome results from chronic compression of the trachea and the mainstem bronchi mainly because of decreased mediastinal diameter. The mainstay of correction is the increase of mediastinal space and the restoration of the tracheal lumen and stability. Owing to the great variability of the manifestation of this disease, individualized approaches are required. We describe our approach in a 36-year-old woman with straight back syndrome associated severe tracheobronchomalacia with reconstruction of the proximal aorta, brachiocephalic artery, sternoplasty, and anterior tracheopexy, which resulted in successful treatment of the condition.

Transoral Minimally Invasive Tracheoplasty Technique for Cervical Tracheomalacia.

We report a case of cervical tracheomalacia successfully treated by tracheoplasty. The resection of redundant posterior tracheal tissue was performed with a novel minimally invasive transoral approach.

Traqueomalacia: diagnóstico y alternativas terapéuticas / Tracheomalacia: diagnosis and treatment options

La traqueomalacia (TM) consiste en una excesiva colapsabilidad traqueal debida a una anomalía estructural del cartílago y/o de la pared membranosa posterior. Cuando se extiende a uno o ambos bronquios principales se denomina traqueobroncomalacia (TBM). Considerando diferentes clasificaciones, la mayoría de las TM son adquiridas, localizadas e intratorácicas. El diagnóstico clínico es difícil porque los síntomas son inespecíficos y se superponen con los de otras enfermedades respiratorias crónicas. Los síntomas más frecuentes incluyen estridor espiratorio, tos perruna e infecciones respiratorias recurrentes, en los casos más graves se presentan episodios de dificultad respiratoria severa, cianosis e incluso muerte súbita. La fibrobroncoscopía sigue siendo el método diagnóstico estándar de oro, complementándose con la tomografía computarizada que es esencial en la visualización de las estructuras adyacentes a la vía aérea. En los casos leves el tratamiento es conservador, considerando la resolución espontánea de la mayoría de los casos hacia los 2 años de edad. En los pacientes más sintomáticos la estrategia terapéutica se debe evaluar caso a caso, siendo la presión positiva contínua en vía aérea (no invasiva o invasiva por traqueostomía) el tratamiento más utilizado. En las TM-TBM más severas, entre posibles tratamientos que incluyen cirugía traqueal y prótesis en la vía aérea, lo más usado es aortoarteriopexia y traqueopexia, a la espera de resultados promisorios de mallas endoluminales biodegradables y prótesis reabsorbibles personalizadas impresas en 3D.

Tracheomalacia (TM) is defined as an increased collapsibility of the trachea due to structural anomalies of the cartilaginous rings and/or the posterior membrane. When the main bronchi is also affected this condition is termed as tracheobronchomalacia (TBM). According classifications TM is mostly acquired, localized and intrathoracic. Diagnosing TM is challenging because symptoms are nonspecific and overlap with those of other chronic respiratory disorders. The most common symptoms include expiratory stridor, barking cough and recurrent respiratory tract infections, in severe cases, severe respiratory distress episodes and acute life threatening events can occur. While flexible bronchoscopy is still considered as the gold standard diagnostic method, computed tomography is essential in assessing the surrounding structures. Conservative therapy is preferred in milder cases since the outcome is usually favorable within the first 2 years of life. Treatment of more symptomatic children should be discussed on an individual basis, continuous positive airway pressure (non invasive o invasive via tracheostomy) being the most widely used therapy. For more severe TM-TBM, amongst possible treatments including tracheal surgery and airway stenting, aortoarteriopexy and tracheopexy are mostly used, nevertheless absorbable stent and 3D printed customed prosthesis are being developed with promising results.

Care recommendations for the respiratory complications of esophageal atresia-tracheoesophageal fistula.

Tracheoesophageal fistula (TEF) with esophageal atresia (EA) is a common congenital anomaly that is associated with significant respiratory morbidity throughout life. The objective of this document is to provide a framework for the diagnosis and management of the respiratory complications that are associated with the condition. As there are no randomized controlled studies on the subject, a group of experts used a modification of the Rand Appropriateness Method to describe the various aspects of the condition in terms of their relative importance, and to rate the available diagnostic methods and therapeutic interventions on the basis of their appropriateness and necessity. Specific recommendations were formulated and reported as Level A, B, and C based on whether they were based on "strong", "moderate" or "weak" agreement. The tracheomalacia that exists in the site of the fistula was considered the main abnormality that predisposes to all other respiratory complications due to airway collapse and impaired clearance of secretions. Aspiration due to impaired airway protection reflexes is the main underlying contributing mechanism. Flexible bronchoscopy is the main diagnostic modality, aided by imaging modalities, especially CT scans of the chest. Noninvasive positive airway pressure support, surgical techniques such as tracheopexy and rarely tracheostomy are required for the management of severe tracheomalacia. Regular long-term follow-up by a multidisciplinary team was considered imperative. Specific templates outlining the elements of the clinical respiratory evaluation according to the patients' age were also developed.

Ultrashort Echo-Time MRI for the Assessment of Tracheomalacia in Neonates.

BACKGROUND: Bronchoscopy is the gold standard for evaluating tracheomalacia; however, reliance on an invasive procedure limits understanding of normal airway dynamics. Self-gated ultrashort echo-time MRI (UTE MRI) can assess tracheal dynamics but has not been rigorously evaluated. METHODS: This study was a validation of UTE MRI diagnosis of tracheomalacia in neonates using bronchoscopy as the gold standard. Bronchoscopies were reviewed for the severity and location of tracheomalacia based on standardized criteria. The percent change in cross-sectional area (CSA) of the trachea between end-inspiration and end-expiration was determined by UTE MRI, and receiver-operating curves were used to determine the optimal cutoff values to predict tracheomalacia and determine positive and negative predictive values. RESULTS: Airway segments with tracheomalacia based on bronchoscopy had a more than threefold change in CSA measured from UTE MRI (54.4 ± 56.1% vs 14.8 ± 19.5%; P < .0001). UTE MRI correlated moderately with bronchoscopy for tracheomalacia severity (ρ = 0.39; P = .0001). Receiver-operating curves, however, showed very good ability of UTE MRI to identify tracheomalacia (area under the curve, 0.78). A "loose" definition (> 20% change in CSA) of tracheomalacia had good sensitivity (80%) but low specificity (64%) for identifying tracheomalacia based on UTE MRI, whereas a "strict" definition (> 40% change in CSA) was poorly sensitive (48%) but highly specific (93%). CONCLUSIONS: Self-gated UTE MRI can noninvasively assess tracheomalacia in neonates without sedation, ionizing radiation, or increased risk. This technique overcomes major limitations of other diagnostic modalities and may be suitable for longitudinal population studies of tracheal dynamics.

The use of expandable metallic airway stent in a baby with tracheomalacia: A case report.

Tracheobronchomalacia is a rare condition in the pediatric age group which may be life-threatening when it occurs. The common form of tracheomalacia is congenital, presenting with wheezing and cough. We report a case of a 65-day-old baby who was treated with non-invasive mechanical ventilation due to respiratory distress since the day of birth. Tracheomalacia was diagnosed based on the physical examination and the thorax computerized tomography (CT) findings. Patient was initially treated with noninvasive positive pressure ventilation and thereafter, fitted with a tracheobronchial conical fully-covered self-expandable nitinol stent. After stent insertion and the respiratory situation of the patient improved, ventilatory weaning and extubation were possible. A careful selection of suitable patients, appropriate stent type and the site, where it has to be placed is mandatory for successful airway stenting. Also, children must be adequately followed-up to prevent the possible life-threatening complications after stent insertion.

Tracheomalacia in bronchopulmonary dysplasia: Trachealis hyper-relaxant responses to S-nitrosoglutathione in a hyperoxic murine model.

BACKGROUND: Bronchopulmonary dysplasia (BPD) with airway hyperreactivity is a long-term pulmonary complication of prematurity. The endogenous nonadrenergic, noncholinergic signaling molecule, S-nitrosoglutathione (GSNO) and its catabolism by GSNO reductase (GSNOR) modulate airway reactivity. Tracheomalacia is a major, underinvestigated complication of BPD. We studied trachealis, left main bronchus (LB), and intrapulmonary bronchiolar (IPB) relaxant responses to GSNO in a murine hyperoxic BPD model. METHODS: Wild-type (WT) or GSNOR knockout (KO) newborn mice were raised in 60% (BPD) or 21% (control) oxygen during the first 3 weeks of life. After room air recovery, adult trachealis, LB, and IPB smooth muscle relaxant responses to GSNO (after methacholine preconstriction) were studied using wire myographs. Studies were repeated after GSNOR inhibitor (GSNORi) pretreatment and in KO mice. RESULTS: GSNO relaxed all airway preparations. GSNO relaxed WT BPD trachealis substantially more than WT controls (P < .05). Pharmacologic or genetic ablation of GSNOR abolished the exaggerated BPD tracheal relaxation to GSNO and also augmented BPD IPB relaxation to GSNO. LB ring contractility was not significantly different between groups or conditions. Additionally, GSNORi treatment induced relaxation of WT IPBs but not trachealis or LB. CONCLUSION: GSNO dramatically relaxed the trachealis in our BPD model, an effect paradoxically reversed by loss of GSNOR. Conversely, GSNOR inhibition augmented IBP relaxation. These data suggest that GSNOR inhibition could benefit both the BPD trachealis and distal airways, restoring relaxant responses to those of room air controls. Because therapeutic options are limited in this high-risk population, future studies of GSNOR inhibition are needed.

Traqueomalacia pediátrica / Pediatric tracheomalacia

RESUMEN La malacia de la vía aérea central puede afectar la tráquea y/o los bronquios, haciéndola susceptible al colapso de sus paredes durante el ciclo respiratorio. Puede clasificarse como primaria o secundaria y clínicamente se manifiesta por síntomas respiratorios recurrentes o persistentes (especialmente en espiración), infecciones recurrentes y en casos severos, episodios de hipoventilación con cianosis. El diagnóstico se establece mediante broncoscopía flexible o rígida. Los estudios de imágenes se consideran complementarios, siendo especialmente útiles en casos de duda diagnóstica, estudio de causas secundarias o para la planificación preoperatoria. Su tratamiento depende de distintos factores como la severidad de los síntomas, su etiología, ubicación y extensión. En casos leves, una observación activa y tratamiento médico en espera de la resolución espontánea en los primeros 2 años, suelen ser suficientes. En casos moderados, la ventilación a presión positiva podría ser de utilidad. En casos severos está indicado el tratamiento quirúrgico, mediante distintas técnicas que buscan dar soporte a la estructura traqueobronquial debilitada, incluyendo traqueostomía, suspensiones directas (traqueopexias) o indirectas (aortopexia), tutores externos o stents intraluminales. En este articulo se revisarán las principales causas y tratamientos disponibles para la traqueomalacia pediátrica. Ya que su diagnóstico y manejo son complejos, es fundamental el trabajo de equipos médicos multidisciplinarios familiarizados con esta patología.

ABSTRACT Central airway malacia can affect the trachea and/or the main bronchi, making their walls susceptible to collapse during the respiratory cycle. It can be classified as primary or secondary, and clinically presents with recurrent or persistent respiratory symptoms (especially on expiration), recurrent infections and in severe cases, episodes of hypoventilation with cyanosis. The diagnosis is established by flexible or rigid bronchoscopy; imaging studies are considered as complementary, especially in cases of unclear diagnosis, secondary causes or for preoperative planning. Treatment depends on different factors such as the severity of the symptoms, their etiology, location and extension. In mild cases, active observation and medical treatment waiting for spontaneous resolution may be enough, which usually occurs in the first 2 years of age. In moderate cases, positive pressure ventilation could be useful. In severe cases, surgical treatment is indicated. Different techniques aiming to provide support to the weakened tracheobronchial structures are available, including tracheostomy, direct (tracheopexies) or indirect suspensions (aortopexy), external splints and intraluminal stents. In this article we present the main etiologies and available treatments for pediatric tracheomalacia. Given that diagnosis and management of these patients is complex, the work of multidisciplinary teams familiar with this pathology is of paramount importance.

Tracheal suspension with autogenous rib cartilage in a patient with severe tracheomalacia.

BACKGROUND: Tracheomalacia (TM), caused by anterior mediastinal tumorectomy, most likely to deteriorate condition of patient life. CASE PRESENTATION: A 63-year-old patient felt serious dyspnea diagnosis as TM caused by the recurrent cervical schwannoma. The narrowest diameter of the TM was only 0.446 cm and the length of malacic segment was 7.47 cm. Here we designed a novel tracheal suspension technique by using autogenous rib cartilage graft to treat severe TM. The obvious effect was observed that the inner diameter increased from 0.446 cm to 1.390 cm,and the airway symptom was alleviated. CONCLUSION: The autogenous rib cartilage graft used for suspending the malacic trachea was safe and effective.

Sudden Airway Collapse After Pneumoperitoneum With Undiagnosed Tracheomalacia in a Morbidly Obese 12-Year-Old Boy Undergoing Laparoscopic Cholecystectomy: A Case Report.

Tracheomalacia is characterized by the collapse of the tracheal wall due to the softening of the tracheal cartilage and myoelastic tissues. We describe the case of a 12-year-old morbidly obese boy, without previous medical issues, scheduled for elective laparoscopic cholecystectomy. Immediately after pneumoperitoneum was established, mechanical ventilation could not be performed. Intraoperative exploration with flexible bronchoscopy showed that the tip of the endotracheal tube was nearly occluded by the posterior tracheal wall bulging anteriorly. Anesthesiologists should be aware of undiagnosed tracheomalacia as a cause of sudden airway collapse, even after the airway is secured with an endotracheal tube.