FRCA Notes

Tracheobronchial stenting

The March 2023 CRQ paper contained a "difficult question" on this topic (56% pass rate).

Relevant information from a somewhat related article on ECMO is included here too.

Resources

  • Airway stents are tracheobronchial prostheses used to both relieve airway obstruction and maintain airway patency
  • They are typically used for treating obstructions or symptomatic narrowing of the central airways i.e. trachea and main bronchi

Type of stent Advantages Disadvantages
Silicone Able to re-position/remove
Less tumour invasion
Less granulation tissue formed		 Requires rigid bronch. to insert
↑ risk of migration (some have external studs to ↓ risk)
↑ risk of infection vs. metallic stents
Metallic (Ni-Ti alloy) Flexible bronch. for insertion
Larger ID:ED ratio than silicone
Self-expanding devices available		 Challenging to re-position or remove
↑ risk of vascular perforation
↑ rate tumour invasion
↑ rate granulation tissue
Hybrid Harness benefit/mitigate risks of each material Expensive
Biodegradeable Removable e.g. temporary stent for tracheal
stenosis post-tracheostomy		 Clinical trials yielded mixed results
Not yet available for clinical use


Malignant disease

  • Respiratory tract
    • Tracheal tumour (31% of central airway obstruction)
    • Primary lung cancer; up to 20 - 30% of those with primary lung cancer develop central airways obstruction
    • Adenoid cystic carcinoma
    • Carcinoid tumours
  • Mediastinal masses (13%) e.g. lymphoma, sarcoma, thymoma
  • Oesophageal tumours
  • Thyroid gland malignancy
  • Compressive effects of breast or colorectal metastases

Non-malignant disease

  • Tracheomalacia or bronchomalacia
    • Congenital e.g. Mounier-Kuhn syndrome
    • Acquired e.g. from chronic respiratory disease, toxin exposure or chronic airway compression (thyroid goitre, vascular abnormalities)
  • Airway fistulas
  • Anastomotic strictures following lung resection or transplantation
  • Tracheal stenosis (20%) e.g. following prolonged intubation or tracheostomy

Symptoms

  • Cough
  • Dyspnoea (± orthopnoea)
  • Haemoptysis
  • Recurrent infection

Signs

  • Wheeze
  • Crackles on auscultation
  • Stridor

  • >50% obstruction considered severe

Perioperative management of the patient undergoing airway stenting


Pre-operative planning

  • MDT assessment by respiratory physician, thoracic surgeon, anaesthetist, radiologist ± palliative care physician ± intensivist
  • Issues to decide upon:
    • Location and severity of obstruction and therefore type of stent to be used
    • Operative technique (e.g. flexible bronch. under sedation vs. rigid bronch. under GA)
    • Need for GA
    • Rescue interventions
    • Post-operative management
    • Ceilings of treatment

History and examination

  • Location and severity of obstruction as above
  • Smoking history
  • Associated cardiopulmonary disease(s)

Investigations

  • Bloods
    • FBC - anaemia
    • U&Es - paraneoplastic phenomena
    • TFTs - especially if thyroid disease is the indication for surgery
  • ECG
  • CXR
  • TTE if risk factors/known cardiac disease
  • CT chest with 3D reconstruction is the optimal imaging modality
  • Lung function tests

  • Optimise co-existing diseases as much as possible, with the acknowledgement that stenting may be a palliative procedure and therefore one should not unduly delay surgery

  • Let us briefly segue into the world of extracorporeal membrane oxygenation
  • With severe tracheal obstruction, GA may precipitate total airway occlusion
  • Among the strategies to mitigate this potentially lethal event is use of ECMO

Classification of airway support ECMO

  • Elective ECMO - full cannulation and initiation prior to surgery

  • Standby ECMO
    • Two 5 Fr gauge sheaths are placed in major vessels and a primed circuit, perfusionist and appropriately sized ECMO cannulae are ready
    • The larger calibre ECMO cannulae aren't placed nor ECMO initiated until haemodynamic instability or inability to oxygenate or ventilate occurs

  • Rescue ECMO - instigation of ECMO without any prior preparation
    • This strategy carries a much higher mortality than the above two

Indications

  • One should consider ECMO as airway procedural support if tracheal patency is less than 5 mm, based on bronchoscopic or CT findings
  • There is some suggestion that the severity of symptoms is a better predictor of intraoperative risk than the degree of airway obstruction, so ECMO should be indicated by this instead
  • I.e. elective/standby ECMO are indicated in adults with severe cardiorespiratory symptoms owing to airway obstruction if general anaesthesia is required

  • The above-linked BJA article has a nifty flowchart to decide which variant of ECMO to use (standby vs. elective, V-V vs. V-A vs. V-VA)
  • In short, if the patient isn't at high risk of perioperative haemodynamic collapse then V-V ECMO is probably preferable; if they are then V-A may be the winner

Conscious sedation

  • Avoid sedative pre-medication as risk of airway collapse
  • Local anaesthetic topicalisation of the airway
  • Judicious use of short-acting opioids for their anti-tussive effect
  • ± THRIVE to minimise risk of inadequate gas exchange

Monitoring

  • AAGBI
  • Dedicated TIVA cannula
  • A-line
  • Depth of anaesthesia monitoring (as usually TIVA technique)

Induction technique

  • Ensure rescue strategy available e.g. rigid bronchoscopy or V-V ECMO
  • Inhalational or IV induction is described - the aim is to:
    1. Induce anaesthesia but maintain spontaneous ventilation so as one can...
    2. Assess the degree of dynamic airway obstruction using flexible bronchoscopy prior to...
    3. Administering a NMBA
  • One can prevent coughing with local anaesthetic topicalisation and adequate depth of anaesthesia

Airway strategies

  • (Obligatory mention of this being shared airway surgery)
  • May be able to use ETT or SAD for flexible bronchoscopy
    • Supraglottic devices benefit from improving access to the proximal trachea and reducing coughing on emergence (and thus the risk of stent migration)
  • THRIVE and tubeless surgery is an option
  • One can maintain oxygenation via the rigid bronchoscope with either:
    • Jet ventilation
    • Ventilation via the side-port of the 'scope

Analgesia

  • Typically not uber-painful
  • Avoid long-acting opioids due to risk of respiratory depression

  • The overall rate of complications is 3.9%
  • The mortality attributed to procedural complications is 0.5%
    • The 30-day mortality his higher compared to that of bronchoscopy for other indications (22.4% vs. 9.7%)

Early complications

  • Trauma to teeth, mouth, oropharynx, airways
  • Barotrauma
  • Complications of jet ventilation e.g. gas embolism, tension pneumothorax, tension pneumomediastinum, subcutaneous emphysema
  • Complications of shared airway e.g. hypoxia, hypercarbia, respiratory acidosis

  • Acute airway obstruction
    • Can occur at any time; induction, mid-procedure, in recovery
    • Can occur post-operatively due to stent migration, airway bleeding, inadequately reversed NMBA
    • Requires rapid use of rescue strategy e.g. rigid bronchoscopy, tracheal intubation or ECMO

Late complications

  • Perhaps ironically more common in those with benign disease as they have a longer life expectancy

  • Stent migration; more likely in isolated tracheal stenting or with the use of silicone stents
  • Stent fracture
  • Within-stent stenosis e.g. due to granuloma formation
  • Stent erosion into surrounding structures e.g. oesophagus
  • Impaired mucociliary clearance, plugging and atelectasis
  • Chronic bacterial colonisation