A bronchoscope with two-way tip deflection is commonly used, although in large dogs a small gastroduodenoscope may be substituted. The bronchoscope should be sterilised prior to use either by cold sterilisation in 2% glutaraldehyde solution such as Cidex (Johnson & Johnson) or Med-Dis^TM (Medichem International Ltd) or using ethylene oxide gas sterilisation. If cold sterilisation is used the instrument must be rinsed and flushed with sterile water prior to use.

Each patient will need to be assessed for anaesthetic risk and the protocol tailored accordingly. In many cases there will be a degree of cardiopulmonary dysfunction and this must be taken into account. Severe cardiac arrhythmia, heart failure or severe hypoxia are contraindications to bronchoscopy.

The patient is anaesthetised and placed in ventral recumbency with the chin propped on a rolled towel and the neck extended. In cats and small dogs anaesthesia may be maintained by topping up the intravenous agent (propofol or alfaxalone) or using continuous rate infusion. However, for most short procedures intermittent intubation and maintenance on isoflurane is preferred in order to provide adequate oxygenation. In medium to large dogs a T-adapter attached to the endotracheal tube allows anaesthetic gas to be continuously delivered with the bronchoscope passed through the endotracheal tube. However, sufficient space must be allowed around the endoscope for adequate flow of gas. In either case it is essential to preoxygenate the patient by mask or endotracheal tube for 10 minutes before commencing the procedure as bronchoscopy will inevitably result in partial occlusion of the airway and a degree of hypoxia. Careful monitoring using pulse oximetry and ideally electrocardiography, is required. End-tidal capnography can also be helpful in prolonged procedures.

A mouth gag is inserted to prevent damage to the endoscope through reflex biting or abrasion of the insertion tube on the teeth. In cats, due to the sensitive nature of the larynx, topical anaesthesia with 1% lidocaine spray is required. The larynx should be examined before intubation and under a very light plane of anaesthesia. Even a moderate plane of anaesthesia may abolish all laryngeal movement. It may be helpful to inject doxopram hydrochloride (1.1 mg/kg i.v.) (Dopram-V) to increase tidal volume and exaggerate laryngeal movements. The larynx should be carefully examined for asymmetrical movement, nodules, hyperaemia, everted saccules or laryngeal collapse.

As in any endoscopic procedure, a routine order of approach helps to ensure a full and thorough examination. The tip of the endoscope is advanced centrally over the top of the epiglottis until the larynx is observed. The endoscope is then advanced slowly down the trachea keeping in the centre of the lumen. The trachea should contain no mucus or foam and should be a uniform pink healthy colour with a smooth wall and easily visible submucosal capillary complexes. Cats tend to have a slightly yellow tinge to the mucosal surface. The tracheal rings should be visible and should nearly meet at the dorsal margin. Overlapping of the rings is not uncommonly found in brachycephalic dogs (tracheal hypoplasia); some small breeds may show evidence of wide 'C'- or 'U'-shaped cartilage rings with a wide redundant dorsal ligament which invades the lumen of the trachea on inspiration giving varying degrees of tracheal collapse. The cross-section of the trachea should be circular and the ligament at the free dorsal margin should be taut. There should be no obvious change in conformation during inspiration or expiration. The carina marks the bifurcation of the trachea into the left and right mainstem bronchi. The carina should be sharp at the point of bifurcation - as should each subsequent division of the lesser bronchi (spurs). A widening and bluntening of the division is an indication of oedema or infiltration.

The tracheobronchial tree is examined as thoroughly as possible, which is largely dependent on the diameter of the bronchoscope used and the size of the patient. Following a 'map' helps with orientation and ensures a more complete investigation of each lobe. The endoscope should not remain in the trachea for more than around 50–60 seconds at a time.

Note is made of any lesions found and samples or biopsy specimens obtained as necessary. Sheathed, protected cytology brushes can be used to obtain cells from specific areas of pathology or biopsy specimens taken from obvious masses. More commonly the most diagnostic yield will come from a bronchoalveolar lavage (BAL).

Bronchoalveolar Lavage Procedure

A BAL may be taken from a site preselected from radiographic findings, a site of obvious pathology seen on bronchoscopy or from a site chosen in the absence of obvious macroscopic pathology. In the latter case the site chosen in usually the middle lung lobe on both sides.

The endoscope instrument/suction channel is flushed with sterile saline followed by air, immediately prior to performing a BAL to remove any contamination. The tip is then directed into the selected lung lobe to a point at which it becomes wedged in the narrow lumen. Sterile 0.9% saline is instilled into the airway via the instrument channel, and immediately aspirated. Up to 2 ml/kg of saline may be used without detriment to the patient; 10 ml aliquots are used in most cats, up to 25 ml in large dogs. The amount aspirated will be about 50–60% of that instilled on the first occasion. The process is repeated at the same site, with the same quantity of saline. Having an assistant percuss the chest between samples may help loosen mucus giving a better yield. Often more can be aspirated from the second sample (60–80%). The samples should be examined for cellularity. A good sample will be slightly cloudy and will froth on agitation due to the presence of surfactant.

Sterile endoscopic catheters can also be used to perform a BAL, and these are passed through the instrument channel into the distal bronchioles but can increase resistance, making instillation and aspiration quite slow and difficult.

Where two sites are sampled they are evaluated separately and the fluid is sent for culture and cytology.

References

1.  Levitan D, Kimmel S. Flexible endoscopy: respiratory tract. In: Lhermette P, Sobel D, eds. BSAVA Manual of Endoscopy and Endosurgery in the Dog and Cat. Gloucester: British Small Animal Veterinary Association, 2008:84–96.

2.  Padrid P. Endoscopic laryngoscopy and tracheobronchoscopy of the dog and cat. In: Tams TR, Rawlings CA, eds. Small Animal Endoscopy. 3rd ed. St Louis, Missouri: Elsevier Mosby, 2011:331–359.