Scoping of the airways is a common diagnostic technique, used to investigate the cause of a variety of different diseases that can affect the respiratory tract.
Correctly termed endoscopy, it involves the use of a piece of equipment called an endoscope — an optical instrument designed to inspect the inside of hollow parts of the body. A type of telescope with its own light source, it can be passed through narrow openings and cavities. The light source illuminates the structure being examined and the vet looks through the telescope to inspect the inside surface of the organ.
Although this technology is most commonly used to view the respiratory tract, endoscopy can be used to examine the inside of other hollow organs including the stomach (termed gastroscopy) and the urinary bladder (cystoscopy). An endoscope can also be passed through a surgical opening such as a trephine, which is a small hole drilled in the head, to inspect the sinuses (sinoscopy).
Records of airway scoping in horses date back to 1888, when vets at the veterinary school in Vienna used an endoscope to examine the upper airways — the nose, pharynx (throat) and larynx (voicebox) — of normal horses, as well as those with certain diseases of these areas. The endoscope was then a rigid telescope, similar to those developed to inspect the inside of gun barrels. These rigid telescopes frequently damaged delicate structures when passed up the nose, resulting in nosebleeds.
In the mid 1970s, flexible fibre optic endoscopes used in human healthcare became available. These endoscopes could be safely manoeuvred around the inside of the respiratory tract and were also thinner and longer, allowing greater exploration of hard-to-access areas.
Most vets now use a video endoscope for airway scoping, so that images can be viewed on a screen in real time.
How it works
The respiratory tract has a complicated structure, but basically consists of a series of tubes that allow air to travel to and from the lungs. This movement of air is essential to allow the body to absorb oxygen into the blood and to eliminate carbon dioxide, a waste product of respiration.
In athletic horses, vast quantities of air need to move into and out of the lungs with each breath. Diseases affecting the airways can seriously compromise the amount of oxygen the horse can pick up, affecting his ability to undertake exercise.
Airway scoping is particularly valuable for detecting problems in the upper respiratory tract, which includes the nose, pharynx, guttural pouches and larynx. It can also be helpful in the evaluation of many diseases of the lower respiratory tract, which comprises the trachea (windpipe), bronchi (smaller airways within the lungs) and lungs.
Examination can take place at the yard or a veterinary clinic. The endoscope is passed through either one of the nostrils — sometimes it may be necessary to use both, in turn. The inside of the airway is then observed as the endoscope is pushed up the nose to reach whichever part of the respiratory tract needs examining.
To reach the guttural pouches, the endoscope must be carefully manoeuvred through the small openings from the pharynx. A flexible wire is sometimes passed through the endoscope to open up the pouch entrance and guide the endoscope inside.
The larynx may need to be evaluated for paralysis or weakness, usually on the left side. In this case, the vet may try to force the horse to take deeper breaths by temporarily closing off the nostrils, which can make it easier to see subtle or mild weakness on the affected side.
Some conditions of the upper respiratory tract that result in airway obstruction (narrowing of the airways) only occur during exercise and cannot be seen at rest. These cases may require scoping during exercise — termed dynamic or overground scoping.
The procedure, which is useful for diagnosing conditions of the larynx and soft palate, involves passing a special endoscope up the nose and fixing this equipment to the bridle. Movements of the larynx and pharynx during fast exercise are then transmitted to a screen using Bluetooth technology and can be viewed in real time.
Risks and limitations
Risks of airway scoping are minimal: the worst possibility is causing a nosebleed. While this may look dramatic at the time, bleeding will invariably stop of its own accord after a few minutes.
The main limitation is the length of the endoscope: provided it has enough tubing, it can usually be passed as far as the main bronchi in the lungs. While generally straightforward, the procedure may be difficult and even dangerous in a horse in severe respiratory distress. Another problem is haemorrhage (bleeding) in the guttural pouches, which can obscure clear viewing of these areas.
Little or no preparation is necessary, although the vet may recommend exercise of the horse immediately before airway scoping takes place. The horse remains conscious. Some form of gentle restraint may be required, such as mild sedation or the use of a nose twitch, and stocks can be helpful to keep him still.
Scoping is not painful, but some horses resent the passage of the endoscope up the nose — especially those that are head-shy.
Two, or preferably three, people are required — one to hold the horse, one to pass the endoscope up the nose and one in charge of the endoscope controls.
What’s the damage?
Results of airway scoping are immediate, because the examination is observed instantaneously. When samples are obtained, however, these need to be analysed in the laboratory.
Where disease affecting the respiratory tract is suspected, scoping may be just one component of investigation.
Other procedures include listening to the chest with a stethoscope, blood sampling, radiography (X-rays) and ultrasound examinations.
Costs will vary between practices and will depend on the precise nature of the examination — whether a tracheal wash is being taken, for example, or investigation extends to the guttural pouches. Expect to pay in the region of £150-250, excluding any visit fees and additional costs for sedation or laboratory tests, or nearer £500 for dynamic airway scoping.
Ref Horse & Hound; 22 November 2018