Pneumothorax (new-mo-thorax) is an abnormal accumulation of air in the pleural cavity which is located between the lungs and the chest wall. Normally there is a small amount of serous fluid in the pleural space which acts as a lubricant during breathing. Air entering the pleural space, results in less room for lung expansion during inhalation and causes the lung(s) to collapse (which is why you the term collapsed lung is often used when describing pneumothorax).
It may be primary or secondary. Primary occurs in otherwise healthy cats, secondary is usually the result of an underlying condition.
Pneumothorax may develop in cats of any age, sex or breed. Cats who roam (particularly intact males) may be at greater risk of traumatic pneumothorax due to their susceptibility to roam and get into fights.
What causes pneumothorax in cats?
There are three classifications of pneumothorax in cats depending on the cause. Traumatic, spontaneous or iatrogenic. Either one or both of the lungs may be affected, bilateral pneumothorax is more common. It may be open or closed. Air can enter the pleural space in one of two ways. From an penetrating wound through the thoracic wall, which allows air to enter from the outside (open), or air leaking from respiratory tract or esophagus into the pleural space (closed).
Open pneumothorax occurs when there is an unsealed opening in the chest wall and is most commonly associated with traumatic pneumothorax. Air is able to enter the pleural space from the external environment during inhalation. This results in a loss of negative pressure in the pleural cavity which is necessary to keep the lung expanded as a result, the lung collapses. When the cat inhales, air is pulled into the chest cavity through the opening.
A rare complication can occur in some cats where a one way valve develops so when the cat inhales air is sucked in, but is unable to exit when the cat exhales, this is known as tension pneumothorax and is life threatening. It can occur with both traumatic and spontaneous pneumothorax.
Closed pneumothorax is where air enters the pleural space from within the lung.
This is the most common cause of pneumothorax in cats. Common causes include:
- Penetrating wounds from gunshots, bites, stab wounds which allow air from outside into the pleural cavity
- Fractured ribs can penetrate the lungs
- Trauma to the lungs which allows air to escape into the surrounding area such as a broken rib
- Trauma from a vehicle
- Fall from a height
- Lung infection
This type of pneumothorax develops without trauma and is always closed. It can be classified as primary or secondary. Primary occurs when there is no obvious underlying cause.
- Pulmonary bleb rupture or bullae emphysema
- Lung flukes
- Pulmonary abscess
- Lung lesions due to cysts, abscess, parasites
- Grass awn migration
- Rupture of the bronchus, trachea, lung or esophagus
Medically induced pneumothorax occurs as a result of surgical procedures such as:
- Thoracostomy tube
- Lung surgery
What are the symptoms of pneumothorax in cats?
As would be expected, breathing difficulties are the most common sign although the extent of symptoms may vary from subtle to severe depending on the severity of the disease. Generally traumatic pneumothorax will be obvious, however this may not be the case with spontaneous pneumothorax, particularly if the leak is slow.
Symptoms may include:
- Cyanosis (blue tinged gums)
- Dyspnea (difficulty breathing)
- Open mouthed breathing/panting
- Tachypnea (rapid, shallow breathing)
- When lying down your cat may lie flat (known as sternal recumbancy)
- Anorexia (loss of appetite)
How is pneumothorax diagnosed?
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. Listening to the chest may reveal abnormal, harsh or even decreased lung sounds.
Routine tests such as complete blood count, biochemical profile and urinalysis which typically come back normal but may be useful in evaluating organ function of cats who have been involved in a trauma such as a road accident or fall.
Thoracocentesis is a procedure which is both diagnostic and therapeutic. It involves insertion of a needle into the chest wall and into the pleural space and air is removed. This both shows that pneumothorax is present as well as relieving symptoms by removing air.
Confirmation of pneumothorax is made via chest x-rays which can also provide additional information such as the extent of pneumothorax as well as possible causes.
CT scan may be performed to look for the bullae, blebs and lung lesions as it is more sensitive than x-rays.
Echocardiogram to look for heartworms in the heart.
Blood tests to look for antigen or antibodies to heartworm or microfilaria.
Fecal examination or tracheal aspiration to look for lung worm or lung fluke eggs or larvae.
Blood oxygen levels may be checked with a pulse oximeter.
How is pneumothorax treated?
Treatment is aimed at addressing the underlying cause, as well as relieving symptoms.
- Medical management may only be necessary in cases of a small and spontaneous pneumothorax. Small tears should heal on their own and the air will be slowly reabsorbed into the bloodstream. Cage rest will be necessary while your cat is recovering.
- Thoracocentesis (see above in diagnosis) to remove trapped air for cases with larger volumes of trapped air.
- Tube thoracostomy (chest tube) may be used in in cases where recurrent thoracocentesis has occurred, a thin tube is inserted into the pleural space to remove air. This tube remains in place so that air can be removed intermittently or continually via a suction unit.
- Surgery will be required for cats with penetrating wounds, grass awns or tumours.
- Surgery may also be required to treat blebs, bullae and lung abscess if medical management isn't successful.
- Analgesics to relieve pain.
- If blood oxygen levels are low, oxygen therapy may be necessary. This can also help to push the free air in the pleural cavity into the pleural blood vessels.
- Other treatments may also be required depending on the underlying cause. Bronchiodilators to treat asthma, antibiotics for pneumonia or lung abscess, anti-parasitic medications for heartworm, lung worms or lung flukes.
Administer medications (if prescribed) as directed by your veterinarian.
Your cat will need to be confined to a large cage or a small room while he recovers. He should not be allowed outside during this period.
Careful monitoring of your cat is essential during this time. If you notice he is developing breathing difficulties again, he needs immediate veterinary attention.