Laryngoscopy, tracheoscopy and bronchoscopy (the last two collectively called ‘tracheobronchoscopy’) are considered valuable procedures for investigating causes of feline lower airway disease. Airway endoscopy is indicated in those patients presenting with stridor, dysphonia, acute or chronic cough, inspiratory or expiratory dyspnea, haemoptysis, and/or unexplained radiographic infiltrates (focal, diffuse, lobar, bronchial, alveolar or consolidation) which have not been diagnosed by other means.^1-4

Despite the potential risks associated with lower airway endoscopy, it can be performed safely in the vast majority of cases. When performed in favourable and controlled conditions, tracheobronchoscopy can still be considered a relatively safe and reliable procedure for the diagnosis, the treatment of respiratory tract disease (e.g., removal of tracheal foreign body) and suction of freshly aspirated materials.⁴

Indications/Contraindications

It’s prudent for the feline practitioner to appreciate that lower airway endoscopy should not be considered to be the first ancillary procedure in these patients. Rather, the suspicion of diseases and the real need for endoscopy to reach the proper diagnosis should only be performed after collecting a full clinical history and performing a full clinical examination, including response to previous treatments (antibiotics, anthelmintics, bronchodilators, etc.). Further tests could include haematology, biochemistry, D. immitis Ab/Ag testing, faecal parasitology and thoracic radiographs. Lower airway endoscopy may then become irrelevant, when radiographic findings include the presence of metastases, mediastinal mass, suspicion of cardiac diseases, pleural disease or diaphragmatic hernia. Laryngeal examination is indicated for cats presenting with airway signs such as dysphonia, stridor or inspiratory/expiratory dyspnoea. Laryngoscopy can be performed easily and should always be incorporated as a routine part of any upper or lower airway endoscopic examination. The differentiation between laryngeal problems and lower airway disease based solely on history and clinical examination is not always obvious in cats. Laryngeal disorders can induce some coughing, but as soon as the laryngeal inlet is reduced, the main signs are dyspnoea and stridor. In cats, the most common laryngeal disorder is laryngeal oedema; tumours and paralysis are less common.⁴ Tracheoscopy is rarely performed on its own as such; however, when performing tracheobronchoscopy the trachea will always be investigated as part of a lower airway endoscopic examination. Tracheoscopy alone would be indicated when a tracheal disorder is suspected based on clinical signs and confirmed on imaging. When tracheal compression or displacement is shown to be due to the presence of an extra- or intrathoracic mass, especially with a mediastinal space-occupying lesion/mass, endoscopy would not be helpful for the diagnosis nor choice of treatment.

Bronchoscopy should be considered in those cases of suspected (or confirmed) lesions of the mainstem bronchi, segmental bronchioles/airways (e.g., FB, neoplasia) and/or for visually-guided intervention and airway sampling. Severe cardiac arrhythmia, heart failure or severe hypoxia are contraindications to tracheobronchoscopy.

Patient Preparation and Anaesthesia

Prior to proceeding with tracheobronchoscopy, the endoscopist should be well versed in normal anatomy and appearance of the feline airways as this will allow for rapid and efficient evaluation, and collection of samples.⁵ The rapidity of the procedure when performed by an experienced endoscopist is one of the key factors in a successful outcome.

Lower airway endoscopy requires general anaesthesia and is, therefore, considered medium-to-high risk in many feline respiratory cases due to the relatively small and higher airway responsiveness of the cat compared to that of the dog. Moreover, as soon as a cat presents as a dyspnoeic patient, the procedure is considered even more of a potential risk of acute respiratory embarrassment during induction, maintenance and recovery phases of general anaesthesia.

Equipment

For cats, a small diameter (e.g., 3–4 mm), flexible fiber-optic or video bronchoscope is preferred over rigid endoscopes. While rigid endoscopes can be used for tracheoscopy, they are much less useful in feline practice as they do not allow examination beyond the carina and there is also risk of airway perforation in the hands of inexperienced operators. Flexible bronchoscopes will also have a ‘multi-use’ biopsy channel in which an adapter can be attached to allow for concurrent oxygen administration, passing biopsy forceps and saline for BALs. Bronchoscopes will usually only have two-way distal tip deflection (up and down). Ancillary equipment used in bronchoscopy includes cytology brushes/aspiration catheters, foreign body retrieval forceps, transbronchial aspiration needles and biopsy forceps.

Often, animals that are candidates for bronchoscopy have compromised respiratory function. There is no such ‘one size fits all’ anaesthetic protocol and each case needs to be treated individually. Most cases tolerate a low-dose acepromazine (0.01 mg/kg), an opioid (e.g., buprenorphine 0.02 mg/kg) and bronchodilator (e.g., terbutaline 1 mg/ml, 0.01 mg/kg IV, IM or SQ), the latter to help reduce bronchospasm and improve oxygenation. General anaesthesia is most easily maintained by total intravenous anaesthesia (TIVA) with incremental doses of propofol or alfaxalone. In cats, due to the sensitive nature of the larynx, topical anaesthesia with 1% lidocaine spray is required.

Technique

The bronchoscope should be sterilised before use, either by cold sterilisation in 2% glutaraldehyde solution such as Cidex (Johnson & Johnson) or Med-DisÔ (Medichem International Ltd), F10 or using ethylene oxide gas sterilisation. If cold sterilisation is used, the instrument must be rinsed and channel flushed thoroughly with sterile water before use.

It’s essential for the operator to be familiar with endobronchial anatomy due to the limited amount of examination time spent within the airways between ‘re-oxygenation’ phases. Common examination method is to evaluate the larynx, trachea, entire right side, and then entire left side in a standard order. Following a ‘roadmap’ will help with endobronchial orientation and ensures a more complete investigation of each lung lobe.⁵

The larynx (both structure and function) should be under a very light plane of anaesthesia. It is vital to have an assistant ‘announce’ phase of respiration to ascertain appropriate abduction on inspiration and adduction on expiration. Unfortunately, cats have airways that are too narrow to allow for the passage of a bronchoscope through a T-adaptor and endotracheal tube. Instead, the bronchoscope is usually advanced directly into the airway under direct visualisation.

The trachea should then be examined down to the level of the carina. It should contain no mucus/foam and should be a uniform pink colour with a smooth wall with easily visible submucosal capillary complexes.

The carina marks the bifurcation of the trachea into the left and right main stem bronchi. The right main stem bronchus is usually straight ahead of the bronchoscope and the left main stem bronchi usually require some manoeuvring to the operator’s right to facilitate entry. For this reason, airway foreign bodies (especially grass blades) are more commonly seen in the right main stem bronchi. Each segmental airway should be evaluated for changes in colour, shape, size, and signs of ‘bubbling’, purulent discharge, excessive mucus, or blood. If the operator becomes ‘lost’, the bronchoscope is retracted back to the carina (landmark) to re-establish position.

Airway Sampling/Bronchioalveolar Lavage

Once the airways have been thoroughly evaluated, samples should be obtained for cytology and microbiology as gross changes are not pathognomonic for specific disease. Airway sampling is best achieved via directed BAL. Samples are obtained by ‘wedging’ the tip of the bronchoscope within a terminal bronchus. Warmed sterile saline is flushed through the biopsy port of the bronchoscope and immediately aspirated. BAL samples should be obtained from at least two sites (usually left and right side) as well as any focal abnormalities.⁴

The retrieved saline is submitted for both cytology, bacterial culture/sensitivity and mycoplasma PCR.

Postoperative Management

The patient is intubated immediately post-procedure and maintained on 100% oxygen until stable and recovered from anaesthesia. It’s essential that patients are closely monitored on recovery and supplemental oxygen administered, either by flow-by or O₂ tent, as required.

Postoperative Complications

The most significant complication encountered post-procedure is upper airway obstruction. This may be due to laryngeal oedema, inflammation and swelling resulting from biopsy or pre-existing lesion, accumulation of mucus/airway secretions or bronchoconstriction. In cases where upper airway swelling/inflammation is anticipated, intravenous dexamethasone may be administered IV (0.05–0.2 mg/kg) before extubation. Additional doses of terbutaline may also be considered to counteract bronchoconstriction.

Conclusion

Bronchoscopy is generally considered a safe procedure, provided there is use of correct equipment for patient size, adequate patient risk assessment, close anaesthetic monitoring and adequate operator experience.

References

1.  Padrid P (2000) Pulmonary Diagnostics. Vet Clin North Am Small Anim Pract 30(6): 1187–206.

2.  Padrid P (2011) Endoscopic laryngoscopy and tracheobronchoscopy of the dog and cat. In: Tams TR, Rawlings CA. eds, Small Animal Endoscopy. 3rd ed. Elsevier Mosby, St Louis, MO: 331–59.

3.  Kuehn NF and Hess RS (2004) Bronchoscopy. In: King LG. ed, Textbook of Respiratory Disease in Dogs and Cats. WB Saunders, St. Louis, MO: 112–8.

4.  Dear JD, Johnson LR (2013) Lower respiratory tract endoscopy in the cat: diagnostic approach to bronchial disease. J Feline Med Surg 15(11): 1019–27.

5.  Caccamo R, Twedt DC, Buracco P et al. (2007) Endoscopic bronchial anatomy in the cat. J Feline Med Surg 9(2):140–9.