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Collapsed trachea

The trachea, or the windpipe, is an important structure that connects the upper airway — the throat — to the lower airway and the lungs. A normal trachea is tubular in shape and made up of a series of C-shaped rings of cartilage connected by a flexible membrane. If these cartilage rings and connective tissues begin to chronically flatten during inhalation or exhalation, the condition is known as tracheal collapse.

Very simply, the trachea can be visualised as a flexible straw. Pressure is applied to it as the dog breathes in and out. As long as the ‘straw’ retains its strength and structural integrity, airflow is unrestricted. However, once it collapses in one or more areas, the structure is permanently weakened and may subsequently collapse more easily and more frequently.

We do not fully understand how the condition develops. Because tracheal collapse is mostly seen in certain breeds of dogs, notably Chihuahuas, Pomeranians, Shih Tzus, Lhasa Apsos, Toy Poodles, and Yorkshire Terriers, a genetic factor is almost certainly involved, but an injury to the throat can also be a cause.

Studies have shown that the tracheal cartilage in dogs with chronic tracheal collapse tends to be deficient in glycosaminoglycans, the building blocks providing structural rigidity to connective tissues. The condition is usually seen in older animals, although it can occur in young dogs.

Clinical signs

There are two types of trachea collapse: cervical, which occurs in the throat area, and intrathoracic, which occurs inside the chest cavity. Cervical collapse occurs during inhalation and intrathoracic collapse during exhalation. It is possible for the collapse to occur in both places simultaneously. Both are characterised by a classic honking cough, often called a ‘goose honk’ cough because of its distinctive honking sound.

The initial signs are usually a mild cough, becoming more persistent. Coughing may be more pronounced during the day, and is mostly seen during or after exercise, excitement, and stress, or from pressure on the trachea from a leash or choke chain.

How is collapsed trachea diagnosed?

A grading system to document the severity of a tracheal collapse was devised by Drs. Tangner and Hobson to aid in determining the best way to treat the collapse. There are four stages of collapse: A grade I classification is characterised by a 25% or less occlusion of the tracheal lumen. Grade II is 25 to 50%, Grade III 50 to 75% and Grade IV is 75 to 100%. Dogs with a Grade I or II collapse are usually good candidates for medical management of the condition.

Tracheal collapse should always be considered when a dog, especially one of the breeds listed above, starts to show signs of a chronic cough. Often, very light pressure over the trachea during a physical examination can raise suspicion of collapsed trachea in a small dog with a persistent dry cough, and a tracheal x-ray may identify the trachea and its shape. The most effective diagnosis is either via an endoscopy and/or a radiographic fluoroscopy of the tracheal area.

A collapsed trachea changes its diameter during the respiratory cycle so we need to see the trachea during both inspiration and expiration. This is best achieved with an endoscopy. A flexible tube with an eyepiece — or sometimes, a video camera — is inserted into the trachea allowing us to watch the trachea during inspiration and expiration, and to see any abnormal collapsing. A radiographic fluoroscopy — a machine which makes a ‘radiographic video’ — also allows us to view the trachea throughout inspiration and expiration.

Many dogs with collapsed trachea will also have heart disease, which can also be the cause of a persistent cough, so the heart is usually evaluated when carrying out a diagnosis for a collapsed trachea.

Treatment protocols

The preferred treatment for tracheal collapse is to medically manage the symptoms through weight reduction and maintenance, stress and exercise restriction, and drug therapy. Drug therapy may include antitussives (cough suppressants), anti-inflammatories, bronchodialators, sedatives, and antibiotics.

Antitussives, most commonly hydrocodone or butorphanol tartrate, are used to reduce the rate of coughing. Anti-inflammatories can help minimise airway inflammation caused by the trauma of the chronic coughing. Bronchodialators, usually theophylline based, are used to dilate the pulmonary airways, which helps decrease intrathoracic pressure during exhalation, hopefully decreasing the degree of tracheal collapse. Antibiotics can be used when the possibility of tracheal infection, known as bacterial tracheitis, exists.

Sedatives may be used in cases where antitussives fail to control coughing spasms. We have had some success using very precisely calculated low doses of ACP once a day during episodes, which have the effect of letting a dog suffering a severe coughing episode to rest and sleep without coughing, allowing time for the airway inflammation to reduce.

None of the medically managed protocols are a cure. The objectives are to reduce the incidence of episodes of tracheal collapse, and to increase the intervals between collapses.

If it becomes impossible to maintain the condition medically there are surgical options available. One that has had some long-term, repeatable success is the application of an extraluminal prosthesis such as a spiral prosthesis or a total ring prosthesis. The prosthesis is applied to the outside of the trachea in order to help it hold its normal cylindrical shape.

This type of surgery has a moderately high success rate, but mostly in younger dogs. Surgical intervention is a last resort but it does offer the advantage that, if successful, the condition is eliminated.