Endoscopic Imaging of the Canine Airway
World Small Animal Veterinary Association World Congress Proceedings, 2004
Brendan M. Corcoran, MVB, Dip Pharm, PhD, MRCVS
Hospital for Small Animals, The University of Edinburgh, Easterbush Veterinary Centre Roslin
Midlothian, Scotland

Bronchoscopy is an invaluable technique for the diagnosis of airway and lung disease in that it allows visual inspection of the trachea and major airways to assess for airway pathology, aids in the localisation and retrieval of airway foreign bodies, and allows accurate sampling from airways and lung areas of interest. In some disease situations bronchoscopy is a prerequisite for accurate definitive diagnosis. It is a routine procedure in the proper investigation of chronic respiratory problems, and is a standard technique in referral centres and beginning to be more commonly available in primary care practice.

The major difficulty most inexperienced operators will have using bronchoscopy is being able to recognise what is normal, and inexperienced operators often over-interpret bronchoscopic findings in order to fit the clinical presentation. However, it should be recognised that in many instances of both acute and chronic respiratory disease, no definite abnormality is identified. This is not necessarily a problem in that it allows the exclusion of certain diseases. The technique will not allow identification of conditions that are exclusively out with the airways, except if they impinge on the airways (mass lesions) or extend to communicate with the airways.

Equipment

The types of endoscopes available varies. Both rigid and flexible endoscopes are available, but the latter type are now becoming more widely used because of their versatility. Flexible endoscopes can be fiberoptic or use video-digital chip technology. The fiberoptic scopes are more commonly used as they are available in affordable sizes. Scopes with a video chip at the tip have tended to be more expensive and reserved for large diameter scopes used in endoscopy of the gastrointestinal system. Fiberoptic endoscopes are produced for both the veterinary and human market. The difference between these two type of scopes is the operating length and the quality of the optics used. Human bronchoscopes usually have 55cm working length and better quality optics, but cannot reach beyond the carina in large or giant breeds of dogs. Veterinary scopes have the advantage of longer working length, but this has to be at the expense of the optic quality (fewer fibres). An alternative is to use gastroendoscopes designed for human use, but these have a wider diameter with greater chance of significant occlusion of the airway. Many veterinary surgeons have obtained second hand or re-conditioned human scopes and this is a cheaper alternative approach. The quality of such scopes can vary. The main problem is the number of damaged fibres, but this can be acceptable if the image quality is not markedly compromised. If acquiring second-hand scopes it is obviously important that a compatible light source is also available.

Directional control of the tip of the scope will be in one plane, unless the scope is of large diameter, when the tip can be move in 4 different directions. Scopes should be handled with care and the excessive sustained bending of the tip (with the control mechanism) should be avoided as should excessive bending of the main body of the scope. All scopes will have a biopsy channel to allow insertion of catheters and biopsy forceps for airway sampling or retrieval of foreign bodies. The catheters tend to be designed for specific use in scopes (semi-rigid, small diameter, sufficient length) and are disposable. Biopsy forceps, however, are expensive and meant for multiple use. They are available in variety of types of working tips, but the most versatile for bronchoscopic use is the cutting/biting tip type. Items should be inserted through the biopsy channel with care, as an internal tear of the biopsy channel will allow water to enter around the fibres causing irreparable damage.

Items should not be inserted in the channel while the tip of the scope is flexed, and ideally should be inserted prior to placement of the scope in the airway.

All scopes need proper care and attention. Cleaning and disinfecting protocols are usually supplied by the manufacturer and should be strictly adhered to. Usually glutaraldehyde based cleaning agents are used, and this has safety implications for staff. Purpose-designed cleaning baths are available, and a worthwhile investment if there is heavy use of scopes. Scopes should be stored hanging and not coiled in the carrying case.

The procedure for carrying out bronchoscopy can vary between operators. General anaesthesia is required in all cases, and as blocking the airway with an endoscope can obviously compromise respiratory function, it is necessary to have proper anaesthetic monitoring by a competent individual. The bronchoscope can be introduced directly into the trachea or through an endotracheal tube, and this is usually done if the endotracheal tube will be too narrow to allow passage of the scope or it is necessary to directly visualise the entire length of the tracheal. If using an endotracheal tube, a side-port adapter is attached (Cobb piece) to allow continued delivery of anaesthetic gases/oxygen. Additional oxygen can be supplied via the biopsy channel when not in use. The patient can be placed in lateral or sternal recumbency according to the operators preference. The authors' preference is left lateral recumbency simply because it is more comfortable to manipulate the scopes position. Prior to carrying out bronchoscopy, thoracic radiographs should be taken in order to identify potential areas of interest which may need careful inspection.

When carrying out bronchoscopy, a rapid inspection is required because of the safety issue mentioned above, and the fact the scope itself acts as a foreign body resulting in a mucosal reaction and mucus production. If both these facts are not appreciated, the operator may endanger the patients safety and make erroneous interpretations. The normal tracheo-bronchial mucosa has a light salmon pink colour along its length. The tracheal mucosa is highly vascular and these vessels are readily appreciated coursing beneath the translucent epithelium. This finding suggests normality. The visibility and number of vessels decreases as the airway size decreases, and are not usually visible in the smaller airways. Identifying the dorsal membrane in the tracheal allows proper orientation and identification of the right and left mainstem bronchi. On the right hand side the cranial lobe bronchus is met first, followed by the middle lobe bronchus. Both of these are seen on the operator's left-hand side. The caudal lobe bronchus is the main continuation of the mainstem bronchus. The accessory lobe bronchus is visualised opening onto the floor of the junction between the mainstem and caudal lobe bronchus at about the 4 o'clock position. On the left-hand side the cranial lobe bronchus can be easily missed, but is located just beyond the carina on the operators right-hand side. It can be difficult to enter, but beyond the entrance it immediately divides into a cranial and caudal division. The left caudal lobe bronchus is the direct continuation of the left mainstem bronchus. Beyond the lobar bronchi there is a nomenclature system for identifying further subdivisions, but in practice can be very difficult to use (Amis & McKiernan 1986).

The possible abnormalities that can be identified are listed in the Table below. Once changes have been documented, the scope is used to guide sampling of the airways and alveoli. For the purpose of successful bronchoalveolar lavage, a bronchoscope is needed. The scope is lodged in a bronchus of interest so as to occlude the lumen. The catheter in the biopsy channel is advanced and the warmed normal saline instilled. To avoid fluid from obscuring vision, it is worth while re-positioning the tip of the scope, and this also allows seeing aspirated fluid traveling through the catheter. The collected material is aliquotted for cytological analysis and culture.

Abnormal Bronchoscopic Findings in Disease

The table below lists the important bronchoscopic findings of the important diseases of the respiratory system and the usefulness of the technique in diagnosis of these conditions.

There are many possible bronchoscopic findings reported for respiratory disease, but some of the more common findings are listed in the following table:

Condition

Bronchoscopic Finding

Comment

Tracheal Collapse

Dorso-ventral flattening of the trachea, primarily at the thoracic inlet, but potentially anywhere along its length and involving the mainstem bronchi.

Definitive diagnostic test, necessary for assessing severity for surgical grading.

Hypoplastic Trachea

Subjective impression that the trachea and carina are narrow and poorly formed.

Radiographic measurement of trachea is much better technique.

Oslerus osleri Infection

Distinct nodules seen at carina with localised inflammatory reaction.

Allows definitive diagnosis once larvae/eggs are retrieved by sampling the nodules.

Chronic Bronchitis

Loss of mucosal vascularity, blanching and/or roughening of the mucosa with localised nodular thickening. Excess mucus material with pooling of exudates in dilated airways (bronchiectasis).

Near-definitive diagnostic test (without mucosal histopathology).

Idiopathic Pulmonary
Fibrosis

Normal, or near normal mucosa, partial collapsing of lobar or smaller airways.

Necessary to differentiate from chronic bronchitis.

Pulmonary Neoplasia

Collapse of larger bronchi primarily during expiration, with appearance of mucoid, blood-tinged mucus or blood.

Very supportive of radiographic findings, but cell identification either on transthoracic FNA or from BALF required.

Bronchopneumonia

Normal mucosa with purulent exudate exiting specific lobar bronchi. Material accumulates at airway divisions, the carina and in the trachea. Can appear normal.

Very supportive of radiographic changes. Allows confirmation an exudative process is present and collection of material for cytology and culture.

References

1.  Amis, TC McKiernan, BD (1986). Systematic identification of endobronchial anatomy during bronchoscopy in the dog. Am J Vet Res, 12: 2629.

2.  Roudebush, P (1990). Tracheobronchoscopy. Vet Clin Nth Amer, 20: 1297.

3.  Veneher-van Haagen, AJ, Vroom, MW, Heijn, A et al (1985). Bronchoscopy in small animal clinics: an analysis of 228 bronchoscopies. JAAHA 21: 521.

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Brendan M. Corcoran, MVB, Dip Pharm, PhD, MRCVS
Hospital for Small Animals, The University of Edinburgh
Easterbush Veterinary Centre Roslin
Midlothian, Scotland


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