Trachea and bronchi Flashcards
In a study by Conguista 2021 in JAVMA, what were the MST for dogs treated medically for tracheal collapse v. endoluminal stenting?
MST for medical management was 3.7 years, and 5.2 years for the stent managed group.
For severe disease the MST for medically managed dogs was only 12 days, as compared to 1338 for stented patients.
In a study by Stordalen 2020 in JSAP, what was the complication rate for tracheostomy tubes placed following BOAS surgery? What were the 3 most common complications?
95% complication rate (although 98% of tubes were ultimately successfully managed).
Three main complications were obstruction, dislodgement, and coughing.
In a study by Suematsu 2019 in Vet Surg, what percentage of dogs survived to discharge following placement of a continuous extraluminal tracheal prosthesis for tracheal collapse? What post-operative complications were reported?
98% of dogs survived to discharge.
Laryngeal paralysis (1/54 dogs), DIC (1 dog), and recurrent tracheal collapse (2 dogs) were reported complications. No dogs developed tracheal necrosis.
Goose honking cough resolved in 96% of dogs.
Survival rate was 86% at 36 months.
What muscle connects the tracheal rings dorsally?
The trachealis muscle (predominantly transversely orientated smooth muscle fibers).
What are the bands of fibrous tissue between the tracheal cartilage rings called?
Annular ligaments
How many tracheal rings do the left and right mainstem bronchi have?
Left: 3
Right: 1
Smaller bronchi have overlapping cartilage plates rather than rings, and loss of these rings denotes the transition to bronchioles.
At what level does the trachea have the smallest cross sectional area?
The thoracic inlet (the widest point is at the cricothyroid junction).
What is the vascular supply to the trachea?
The trachea receives segmental blood supply from the cranial and caudal thyroid arteries. At the level of the carina the blood supply switches to the bronchoesophageal arteries.
Venous drainage is via the thyroid, internal jugular and bronchoesophageal veins.
Where does lymphatic drainage from the trachea flow?
Deep cervical, cranial mediastinal, medial retropharyngeal, tracheobronchial lymph nodes.
What is the main innervation to the trachea and trachealis muscle?
The right vagus and recurrent laryngeal nerve.
What is the ratio of the trachea to thoracic inlet in dogs?
Normal: 0.20
Brachycephalic: 0.16
English Bulldog: 0.13
What are some imaging techniques that can be used in assessment of the trachea?
Radiography: can assess tracheal size, may see pulmonary changes in instances of tracheal obstruction (underinflation with proximal obstructions, overinflation with distal obstructions).
Fluoroscopy: useful for assessment of dynamic conditions and interventional radiology techniques.
CT: more accurate for measurements of tracheal diameter (less underestimation). Also used for radiation planning and detection of location of tracheal rupture.
Tracheobronchoscopy: allows for grading of airway collapse, diagnosis of bronchomalacia, and collection of samples via bronchoalveolar lavage.
What are some contraindications to temporary tracheostomy tube placement?
Obstruction distal to the tracheostomy site, tracheal collapse distal to the tracheostomy site, tracheal stent.
What are the options for temporary tracheostomy tube placement?
Transverse, tracheal flap, vertical.
When performing a transverse temporary tracheostomy, the incision length should not exceed what?
Half the circumference of the trachea.
What size endotracheal tube in relation to tracheal diameter should be used for temporary tracheostomy?
Ideally 75% of the tracheal diameter.
Allows for continued flow around the tube in the case of obstruction, and helps to prevent silent death.
Should the cuff of a temporary tracheostomy endotracheal tube be inflated?
No, not unless positive pressure ventilation or anesthetic gases are required. Inflation causes an increase in airway pressure and can cause mucosal damage.
If inflation of the cuff is necessary it should be deflated every 4-hours and repositioned.
Ideally high-volume, low-pressure cuffs should be used.
What can occur with uninterrupted suction of a temporary tracheostomy tube?
Atelectasis, hypoxia, vagal response.
How often should E-tubes be exchanged when placed in a temporary tracheostomy?
At least twice daily (double lumen tubes allow for exchange of just the inner portion of the tube without whole tube replacement).
What are some acute complications associated with temporary tracheostomy?
Occur in 50% of cases; plugging of the tube, inadvertent removal, gagging, coughing, vomiting, SC emphysema, pneumomediastinum, pneumothorax, infection, respiratory distress.
Cats may experience a higher rate of tube obstruction due to greater mucus production.
What is the most significant long-term complication associated with tracheostomy?
Stenosis (either at the stoma or at the location of the cuff or tube tip). Loss of 18-25% of the tracheal lumen is common.
Use of low pressure cuffs may help to reduce damage.
What are the most common indications for permanent tracheostomy?
Cats: laryngeal masses.
Dogs: laryngeal paralysis or collapse.
Placement of permanent tracheostomies are recommended above which level of the trachea?
12th tracheal ring. Mortality rates of 57% reported below this level due to airway obstruction and excessive kinking.
How long does it take for mucous secretions to reduce following permanent tracheostomy?
1 month (they are initially increased due to squamous metaplasia of the tracheal mucosa which takes 16 weeks to resolve).
What are the most common complications associated with permanent tracheostomy?
Cats: mucus plugs in the respiratory tree.
Dogs: aspiration pneumonia and the need for revision surgery (stenosis commonly reported).
What degree of stenosis of the tracheostomy site can be expected post-operatively?
60%, however too-large stoma should be avoided as it may cause tracheal collapse. If collapse is already present support of the stoma should be provided through the use of extraluminal rings.
How are small wounds of the trachea or bronchi closed?
Simple interrupted manner using a mattress pattern or other tension relieving suture.
How much luminal stenosis is required for clinical signs to result?
50-75% stenosis.
At what tension will stenosis occur following tracheal resection and anastomosis?
750 g, at double this tension circumferential stictures are documented.
What are some methods of tension relief for the trachea?
There is inherent tension on tracheal repairs due to the elasticity of the peritracheal tissues.
Tension relieving techniques include;
1. Tension relieving sutures placed several rings proximal and distal to the anastomosis.
2. Fixed ventroflexion of the neck.
3. Release of the annular ligaments with preservation of the mucosa.
What percentage of the trachea can be resected in adult and juvenile dogs?
Adult: 50-58%
Juvenile: 20-25% (the juvenile trachea only withstands 60% of the force of the adult trachea due to higher water content and less collagen).
Why are non-absorbable and braided sutures not preferred for tracheal anastomotic closure?
Higher rates of stricture and granulation formation (non-absorbable).
Luminal stenosis may also be less severe when an interrupted pattern is used (potentially due to less effect on the local blood supply).
What are some techniques described for tracheal resection and anastomosis?
Annular ligament cartilage technique, split cartilage technique are most commonly described in dogs.
Other techniques include direct suturing of preserved cuffs of mucosa, suture placement through cartilage rings (not recommended in old or juvenile animals), overlapping anastomoses, and step anastomoses.
Is the annular ligament or split cartilage anastomosis technique preferred for tracheal anastomosis in dogs?
Split cartilage technique might result in less dorsoventral luminal stenosis and more precise alignment, although some degree of stenosis was noted in 80% of dogs with both techniques.
What surgical approach is preferred for access to the intrathoracic trachea?
3rd to 5th right intercostal thoracotomy. The azygous vein can be ligated and transected to maximize exposure. Care must be taken to preserve the vagus, phrenic, and recurrent laryngeal nerves.
How can the seal of a tracheal resection and anastomosis be tested?
Leak testing with 20 cmH20 of positive pressure ventilation.
Following resection and anastomosis of the trachea how much of a reduction in mucociliary clearance is seen?
3 fold reduction, typically reestablishing by the following month.
What is the most common cause of tracheal rupture in cats?
Iatrogenic rupture secondary to endotracheal intubation.
What is the most common clinical sign in cats with tracheal rupture?
SC emphysema (100%) +/- pneumomediastinum, pneumoretroperitoneum, pneumothorax.
How is tracheal tear diagnosed?
Tracheobronchoscopy +/- CT
What are medical management options for cats with tracheal rupture?
Oxygen supplementation, cage rest, sedatives. SC emphysema typically takes 2 weeks to resolve.
When is surgical intervention warranted for cats with tracheal rupture?
Worsening dyspnea, lack of response to oxygen, worsening SC emphysema.
Where do tracheal tears typically occur in cats following endotracheal intubation?
At the junction of the tracheal rings and the trachealis muscle.
Where does tracheal avulsion injury typically occur?
At the weakest point of the intrathoracic trachea (1-4 cm proximal to the tracheal bifurcation).
What might form secondary to untreated tracheal avulsion?
A pseudoairway might form, composed of granulation tissue and fibrosis. These patients typically present 2-3 weeks after the injury with signs of airway obstruction as scarring and stricture advance leading to airway compromise.
What imaging findings are typical of tracheal avulsion?
Pneumomediastinum +/- pseudoairway formation.
What is the treatment for tracheal avulsion?
Resection and anastomosis. Typically yields good results.
Why are tracheobronchial foreign bodies uncommon?
May cause acute death and/or are rarely retained (expelled through coughing).
What imaging techniques might be required for diagnosis of tracheobronchial foreign body?
Radiography (only 66% accuracy for localizing the foreign body), tracheobronchoscopy, CT.
What treatment options are available for removal of tracheobronchial foreign bodies?
- Tracheobronchoscopy (can be difficult and time consuming), fluoroscopic guided removal (sacrifices visualization but allows for passage of a smaller instrument with less impact on subsequent oxygenation).
- Surgical removal: thoracotomy (right sided) with tracheotomy or lung lobectomy.
Obstruction of how much of the trachea is required to produce clinical signs associated with tracheal neoplasia?
50%
Are esophagotracheal and esophagobronchial fistulae more commonly congenital or acquired?
Acquired, typically secondary to an esophageal foreign body.
Esophageal diverticula are frequently seen in conjunction and may predispose to foreign body entrapment.
How are esophagotracheal and esophagobronchial fistulae typically diagnosed?
Contrast esophagram (avoid the use of iodinated contrast as it can cause pulmonary edema).
Tracheobronchoscopy and esophagoscopy can also be used but are not always successful in identifying the fistula.
What is the treatment of esophagotracheal and esophagobronchial fistulae?
Normally lung lobectomy is required with concurrent closure of the fistula.
What changes to the tracheal cartilage are thought to result in tracheal collapse?
Decreased water content (reduction in glycoprotein and glycosaminoglycan) and replacement of hyaline cartilage with collagen and fibrocartilage results in increased compliance and decreased rigidity.
Loss of normal tracheal epithelium due to coughing results in production of increasingly viscous mucous secretions.
In what percentage of dogs with tracheal collapse is coughing elicited on tracheal palpation?
41%
What imaging techniques can be used for diagnosis of tracheal collapse?
Radiography: variable sensitivity (60-90%).
Fluoroscopy: useful for dynamic assessment. Detects significantly more sites of collapse during cough compared to radiography and bronchoscopy.
Tracheoscopy: allows for direct visualization and collection of samples. Evaluation of the airway during cough is limited.
What is the grading system used to describe tracheal collapse?
Grade 1: 25% collapse,
Grade 2: 50%
Grade 3: 75%
Grade 4: 100%
What acute and chronic medical management therapies have been described for tracheal collapse?
Acute: oxygen, sedatives, cough suppressants, corticosteroids +/- endotracheal intubation if severe.
Chronic: corticosteroids, weight loss, use of harness rather than a neck collar, removal of airway irritants (smoke, dust, scented candles, etc), airway nebulization/humidification, bronchodilators (minimize small airway obstruction and reduce intrathorocic pressure).
Medical management has been described to be successful in 71% of cases for longer than 1 year.
Which patients with tracheal collapse should be managed surgically?
Patients with grade II-IV tracheal collapse in which medical management has failed.
It is worth noting that if coughing is not resolved with medical management, limited palliation is expected with interventional procedures.
What are some surgical options for treatment of tracheal collapse?
- Extraluminal prosthetic rings
- Extraluminal spiral prosthesis
- Intraluminal stents
What percentage of patients treated for tracheal collapse with extraluminal prosthetic tracheal rings don’t require medical therapy post-operative?
65%, MST of 1680 days reported in one study.
What are some potential complications associated with the use of extraluminal tracheal rings for tracheal collapse?
Laryngeal paralysis (11-30%), tracheal necrosis, tearing of the trachealis muscle, collapse beyond the rings, migration of the prosthesis, pneumothorax.
What are some techniques to prevent tracheal necrosis during placement of extraluminal tracheal rings for tracheal collapse?
Skeletonization of the vasculature during placement of extraluminal tracheal rings may disrupt the blood supply leading to cough, SC emphysema and death.
Methods to prevent this include;
1. Skeletonization of only one-side of the trachea (right side is recommended as there is more room between the recurrent laryngeal nerve and trachea on this side).
2. Tunnelling of the implants (extreme care must be taken not to inadvertently damage the recurrent laryngeal nerve).
What is the purported benefit of an extraluminal spiral prosthesis over extraluminal tracheal rings for use in the treatment of tracheal collapse?
Uniform, rather than segmental, support of the trachea.
Requires a thoracotomy to facilitate distal placement and is rarely used.
What are some advantages of the use of intraluminal stents for tracheal collapse?
Can treat intra- and extra-thoracic tracheal collapse, shortened anesthetic time, immediate improvement in clinical signs.
What type of stents are used for intraluminal stenting of tracheal collapse?
Nitinol wire, wound, reconstrainable, foreshortening stents are recommended (can be recaptured).
Laser cut stents do not foreshorten but have an unacceptable rate of fracture.
What diameter of stent is used in tracheal stenting for trachea collapse?
A stent diameter that exceeds the tracheal diameter by 10-20% on positive pressure thoracic films is chosen. Radiography underestimates tracheal diameter by 1mm and CT may be more accurate.
Should span from 1cm caudal to the cricoid cartilage to 1cm cranial to the carina. Inappropriate placement can result in laryngospasm, laryngeal dysfunction, paroxysmal cough, and entrapment of bronchial secretions.
What post-operative medications are recommended following tracheal stent placement?
Antitussives, glucocorticoids, sedatives, antimicrobials.
What is the MST for dogs treated with intraluminal tracheal stent?
365 days (compared to 1460 for extraluminal prosthetic rings, although patients with intraluminal stenting were significantly older).
What are some potential complications associated with intraluminal tracheal stenting?
Stent fracture (often a sequelae of persistent cough), stent migration, obstruction of the stent with granulation tissue (secondary to cough, stent motion, respiratory infection), collapse beyond the stented region, tracheal rupture.
What are some management options in instances of tracheal stent fracture?
Aggressive medical management, deployment of a new stent within the fractured stent, placement of extraluminal prosthetic rings, removal of the stent via tracheotomy or resection and anastomosis.
How can excessive inflammatory tissue formation around a tracheal stent be managed?
Corticosteroids, colchicine, treatment of concurrent tracheitis.
In what percentage of dogs with tracheal collapse is bronchial collapse observed?
71-83%. Often dynamic (59%).
Right middle lobar, accessory, left cranial, and left caudal bronchi most common affected.
Signs typically improve with tracheal stenting, although bronchial stenting can be performed.
What causes congenital lobar emphysema? Which lung lobe is most frequently affected? What is the treatment?
Congenital abnormality in cartilage within the bronchioles leads to collapse during exhalation and trapping of air within the alveoli.
The right middle lung lobe is most frequently affected. Pekingese are overrepresented.
Treatment is by lung lobectomy.
What is bronchiectasis?
Chronic, irreversible damage to bronchi that develops as an end-stage change most frequently secondary to pneumonia. Characterized by bronchi wall destruction and mucus accumulation.
Most common in the right cranial lung lobe, but normally multiple lobes (89%).
Lung lobectomy may be possible if a single lobe is affected.
