Introduction

Respiratory procedures require relatively small diameter, flexible instruments. Although rigid equipment can be used, flexibility is necessary to obtain a good examination. Flexible bronchoscopes are much like flexible gastroduodenoscopes except that the bronchoscopes are a) smaller in diameter (e.g., 5–6 mm in most cases, although there are some “ultra-thin” scopes with diameters <2–3 mm), b) do not have the ability to wash off the lens, c) are shorter, and d) have a tip that will flex in one plane only. There is a biopsy channel (typically 2.0 mm in diameter) which can be used for performing washes or aspirations, passing biopsy instruments or a foreign body retrieval device, and administering oxygen during some bronchoscopic procedures. In larger dogs, one can often use pediatric flexible gastroduodenoscopes for these procedures. However, in animals weighing less than 10–15 kg, it becomes excessively hard to use flexible gastroduodenoscopes with outer diameters >7.9 mm (a major problem is that they are so large that they tend to occlude the trachea during the procedure). When examining the posterior nares, it helps to have a scope with a narrow flexing radius so that there is less pressure in the posterior nares (and hence less propensity to gagging).

Biopsy instruments are used through bronchoscopes just as for gastroduodenoscopes. However, they are not used as frequently. The most useful instruments used through bronchoscopes include sterile polypropylene tubes for washes and aspiration, and covered brushes for obtaining samples for cytology. Brushes can be particularly useful for obtaining a “deeper” cytology of an area. They should be used only once, because it can be extremely hard to adequately clean them off after use, and today’s sample may be contaminated with last week’s sample if the brush is reused without scrupulous cleaning in between uses. Likewise, it is best to use aspiration tubes once and then discard them. We make our own at minimal expense by attaching soft plastic tubing and blunt needles. Because the foreign bodies found in the respiratory tract tend to be much different than those found in the alimentary tract, one seldom needs such a wide array of devices as are needed for gastroduodenoscopes. Biopsy cup forceps and “W”-type coin retrieval forceps are usually more than adequate (although occasional odd objects are found that require specialized equipment).

Bronchoscopy

Bronchoscopy is primarily indicated in animals with pulmonary parenchymal or airway disease such as coughing, exercise intolerance, stridor, or dyspnoea. This is especially true when the more common causes have been eliminated. Brush cytology or directed washings (e.g., bronchoalveolar lavage) are often particularly useful. The primary reason bronchoscopy becomes an emergency procedure is when patients are dyspneic/hypoxic and the suspected cause is obstruction. The most common causes of obstruction are laryngeal/pharyngeal disease (e.g., everted lateral saccules), collapsing trachea, tracheal-bronchial foreign body, and tracheobronchial mass [tumour or granuloma]).

No special preparation is needed before this procedure, and in the case of emergencies, there is no time for such. Narcotic preanaesthetics (e.g., oxymorphone, 0.05 to 0.1 mg/kg, or butorphanol, 0.22 mg/kg, followed by an anticholinergic) can make the examination easier by suppressing coughing. If only the lower airways will be examined to remove a foreign body or mass or perform a bronchoalveolar lavage or a brushing, then it is acceptable to induce anaesthesia with a barbiturate or propofol and then maintain with isoflurane. The bronchoscope can be passed through the endotracheal tube if it has a large enough diameter. However, one must be very careful to make sure that the bronchoscope does not obstruct the endotracheal tube and suffocate the patient. If the endotracheal tube is too small to allow the scope to be used, then one must use injectable agents to maintain anaesthesia. Propofol (4 to 6 mg/kg) may be given to effect to maintain anaesthesia; it is noncumulative and can be given as needed. Oxygen may be insufflated through the biopsy channel of the endoscope during the examination. However, it is important to not obstruct the airway with the scope and cause barotrauma. If the patient is maintained by injectable rather than inhalant agents, a mouth gag is necessary.

Foreign Bodies

The removal of foreign bodies in the respiratory tract is usually not too much different than removing them from the GI tract. The same retrieval devices are used, and the techniques are the same. However, one foreign body that can be particularly difficult is the broken canine tooth that heads down the respiratory tract point first. This results in the endoscopist finding a “blank wall” (i.e., the broad surface of the broken canine) which effectively plugs the bronchi and makes it very difficult to find a place to grab the foreign object. The most effective technique is to use W-type coin removal forceps and try to force the edges of the forceps between the bronchi and the edge of the broken tooth. Finding seeds and small sticks can be difficult if the foreign object has been there for any length of time. The longer the foreign object is present, the more mucopurulent mucoid exudate accumulates around it, making it harder and harder to see. Finding that one bronchus is filled with such mucus is a sign that it needs to be investigated. The endoscopist should carefully insert partially opened alligator forceps and blindly grasp and pull. Do not pull too hard in case you have accidently grabbed bronchus instead of a foreign body.

Tracheal Collapse

This is a common event. The value of endoscopy is that it can diagnose cases that are missed by fluoroscopy (yes, you can have severe tracheal collapse and not see it on fluoroscopy). Respiratory endoscopy can better define the extent and severity of the collapse. If the patient is dyspneic under anaesthesia, it can be hard to pass the scope through the larynx. Aim the tip of the endoscope for the ventral most aspect of the laryngeal opening and slide the tip along this ventral surface. If you are insufflating air while you do this, you can usually improve the patient’s oxygenation. If a stent is needed, that is best performed under fluoroscopic imaging.

Lung Lobe Torsion

An uncommon event, it is important. One can often see the bronchus of the affected lobe literally twisting and closing off that particular lung lobe.

Respiratory Tract Bleeding

Bronchoscopy is usually a diagnostic procedure in patients with respiratory tract bleeding because most sources of bleeding are deeper in the lung parenchyma as opposed to the trachea or major bronchi. Therefore, bronchoscopy is usually used to determine which lung lobe needs to be resected. In rare cases the source of the bleeding will be in the trachea and bronchi and can be cauterized or removed.

Tracheal Tears

This is usually due to placement of an endotracheal tube, and especially in cats. Such a tear is an absolute contraindication to scope the respiratory tract of the patient. First, you may or may not be able to find the tear, but you will almost certainly worsen the tear during the procedure. Second, this is not an indication for surgery unless the tear is so severe that it is resulting in a tension pneumothorax (and this is exceedingly rare event). Just put the patient in a cage and leave it alone. The tear will eventually seal over without problem.

Diagnostic Procedures

Sternal or lateral recumbency is used unless a bronchoalveolar lavage is going to be done, in which case lateral recumbency with the side to be sampled placed down is necessary. The scope is lightly lubricated and carefully advanced through the arytenoids or the endotracheal tube. When you reach the carina, you should carefully examine each bronchus by advancing the scope as far into it as possible. Do not advance the scope if you feel resistance, even if the path in front of you seems to be “wide open.” Remember that the scope is larger than the image seen. It is especially easy to tear the feline trachea.

For bronchoalveolar lavage, you should gently advance the tip of the scope or a sterile tube as far as possible into a particular dependent bronchus. Be sure that you do not completely occlude the airway, and then instill sterile, physiologic saline solution into the bronchus. We usually use 25 mL aliquots in dogs and 5 mL/kg aliquots in cats. Aspirate it immediately after you have instilled it. In dogs, you should repeat the procedure on the same lung lobe. Dogs and cats with respiratory disease can become hypoxic for anywhere from several minutes to a few hours right after the bronchoalveolar lavage. These patients may need respiratory support (i.e., an oxygen cage and bronchodilators).

Examination of the Choana

The animal must be in a very deep plane of anaesthesia or it will gag. A narcotic pre-anaesthetic is recommended. A cuffed endotracheal tube is mandatory if a biopsy will be done. The patient is best positioned in sternal recumbency. The mouth is held open with a strong mouth gag, and then the tongue is pulled forward while the tip of the scope is placed beyond the caudal margin of the soft palate. The tip of the scope is then maximally deflected dorsally. At this point, you should be able to see the choana. If a biopsy is desired, it is best to place the biopsy instrument into the biopsy channel such that the tip is just about ready to protrude from the tip before retroflexing the tip of the scope. Trying to force the biopsy instrument through the channel after maximally deflecting the tip can easily damage or destroy the scope. The most common findings in this area are foreign objects and tumours.

Choanal Foreign Bodies and Strictures

If an animal vomits vigorously, a foreign body may by propelled past the base of the tongue and into the choana. One must be careful in trying to remove such foreign bodies because the tip of the scope is maximally retroflexed (making it easier to damage the biopsy channel of the insertion tube). Sometimes such foreign bodies can be pushed out by vigorously flushing large volumes of water into the nose under as much pressure as possible. Strictures may occur at the choana, obstructing the posterior aspect of the nasal cavity. Such strictures are potentially very difficult to treat, and these cases should be referred to a specialist with experience in such cases.

Electrocautery

Use of electrocautery in the respiratory tract is an uncommon event. The following discussion presupposes that the clinician has experience with endoscopic electrocautery (typically in the GI tract). If you do not know and fully understand concepts such as “current density” and “capacitance” as well as the fundamentals of polypectomy and how to protect both the patient and the endoscope, you should not attempt electrocautery in the respiratory tract.

It is especially important when working in the relatively cramped space of the respiratory tract to keep the tip of the electrocautery probe or snare away from the tip of the endoscope. If you activate the electrosurgery device when the tip of the instrument is in close proximity to the tip of the endoscope, it is possible to send a current up the insertion tube and even into the video processor. While this is a rare occurrence, it has the potential to destroy the camera in the tip of the insertion tube and the video processor (both of which are potentially expensive propositions).

However, the most important consideration is the fact that activating the almost any electrocautery instrument in the respiratory tract when oxygen is being infused is almost guaranteed to kill the patient. Such an action can literally ignite the tracheal/bronchial mucosa and burn up the epithelium of the entire system of airways. This has happened in people and there is no reason to believe it will not happen in dogs and cats. Insufflation of room air through the endoscope during the procedure will generally be sufficient to support the patient and allow the procedure to occur safely.