Anjop J. Venker-van Haagen, DVM, PhD, ECVS
Diagnostic imaging always precedes bronchoscopy.
The usefulness of bronchoscopy in the diagnosis of diseases of the tracheobronchial tree in the dog and the cat is well recognized. The equipment has been described and bronchoscopic findings in the dog and cat have been illustrated.2,14,48 Although the cost of good-quality equipment is substantial, it is a worthwhile investment for the more specialized small animal practitioner. Videoendoscopy is ideal for teaching, since a group of students can follow the bronchoscopic examination in real time. Bronchoscopic technique differs according to whether a flexible or rigid bronchoscope is used. Rigid systems are less expensive and much more durable. Several sizes of high-quality rigid bronchoscopes can be purchased for the price of just one size of a good-quality flexible bronchoscope. The advantage of the flexible bronchoscope in human medicine is that it makes bronchoscopy possible without anesthesia, but this is in any case never possible in dogs and cats. On the other hand, the thorax is narrower laterally in dogs and cats than in humans, which facilitates access to all bronchial divisions using rigid bronchoscopes. The details of bronchoscopy using rigid instruments are therefore described in what follows.
Bronchoscopy Using Rigid Instruments
Bronchoscopy is used to inspect the larynx, the trachea, and the bronchi. Rigid bronchoscopes are available both in small sizes for use in humans and in equipment specifically designed for dogs and cats. For dogs we use bronchoscopes in four sizes: 30 cm × 4 mm, 30 cm × 6 mm, 40 cm × 9 mm, and 50 cm × 9 mm. Each is provided with both a 180°-vision and a 90°-vision telescope, except the longest bronchoscope, which was developed as an esophagoscope for humans. For cats there is a 35 cm x 3.6 mm bronchoscope with a 2.9 mm telescope. Foreign body forceps and biopsy forceps are available for each size of bronchoscope. Long flexible catheters and rigid cannulas for suction, together with a flush and suction system for 10 cc saline solution, are used to obtain material for culture and cytological examination. An adjustable headrest for the animal is a must when rigid endoscopes are used. Illumination can be provided by a simple light source, a flash generator for photography, or a light source for video equipment.
Bronchoscopy differs entirely from rhinoscopy in that the anesthetic risks are often high. The reason for performing bronchoscopy is usually deficient lung function associated with severe bronchitis or obstructive disease. Oxygen administration is therefore necessary before, during, and after bronchoscopy. It is also essential that the ECG, the pulse, and the adequacy of oxygenation be monitored by an experienced anesthesiologist who is able to anticipate changes in ventilation and perfusion of the lung and changes in heart action.
Visual Recognition of the Lesions
Diagnosis often depends not only on the visual recognition of lesions in the trachea and bronchi but also on acquisition of material under visual control for cytological examination and culture. Fluid obtained by flushing the main stem bronchi with physiological saline solution at body temperature usually provides adequate material for diagnosis of bronchial diseases. When alveolar washing is required for measurement of specific surfactant, the bronchoscope is wedged into a more peripheral bronchus before flushing with saline solution. This technique is not used routinely because the results are of no consequence in the diagnosis of common bronchopneumonias.
Bronchoscopy is always preceded by radiographic examination of the trachea and thorax. In dogs, anesthesia is then induced with medetomidine and propofol in doses according to the risk status of the dog. In cats anesthesia is induced with acepromazine, ketamine, and atropine. The cat is very sensitive to vagal stimulation during bronchoscopy and if not prevented this causes a massive production of fluid in the bronchi and sometimes death due to acute heart failure. Induction of anesthesia in both dogs and cats is completed by endotracheal intubation and instrumentation of the patient for monitoring. The patient is then placed in dorsal recumbency with its head on the headrest. When the patient is stabile the endotracheal tube is removed and the bronchoscope, through which oxygen is administered, is introduced with the right hand while the epiglottis is lifted with the laryngoscope in the left hand. After inspection of the larynx the bronchoscope is introduced into the trachea and the telescope is fitted into the bronchoscope. After inspection of the cervical trachea, the headrest is elevated and the bronchoscope, with the telescope, is introduced into the thoracic part of the trachea, bringing the carina into view. The bronchoscope is carefully moved caudally to pass the carina into the right main stem bronchus (in dorsal recumbency, the patient's left and right correspond to the bronchoscopist's left and right). By moving the head on the headrest slightly to the left, the orifices of the right cranial bronchi are inspected. For the inspection of the intermediate bronchus the headrest and head are moved to the right. The bronchi of the caudal lobe are straight ahead, while for deeper parts of the cranial and cardiac bronchi the 90°-angle vision telescope is used. When the inspection of the right bronchi is completed the bronchoscope is retracted and then introduced past the carina into the left main stem bronchus. The headrest and the head are moved to the right until there is a clear view of the entire left main stem bronchus. The orifices of the lingula (the combined orifice of the left cranial and cardiac bronchi) and the bronchi of the left caudal lobe are inspected. For deeper inspection of the bronchi of the left cranial and left caudal lobes the 90°-angle vision bronchoscope can be used. The bronchoscope is then carefully retracted. Bronchial material is routinely obtained for culture and cytology by flushing and retrieving the fluid, and biopsies are obtained for histological examination if specifically indicated.
1. Venker-van Haagen AJ. Trachea and bronchi. In: Ear, Nose, Throat, and Tracheobronchial Diseases in Dogs and Cats. Hannover: Schlütersche Verlagsgesellschaft, 2005: 167-205.