What is pneumothorax, and what are the different types?
Fig. 1: X-ray of a dog's chest, showing pneumothorax. The heart is lifted off the sternum by the air that has entered the chest cavity.The term pneumothorax refers to the abnormal accumulation of air in the space surrounding the lungs. The presence of air between the lungs and the chest wall prevents the lungs from inflating normally, causing difficulties breathing, increased respiratory rate, chest pain, and possibly lung collapse.
Pneumothorax has several possible causes, including trauma to the chest, underlying lung disease, and excessive pressure on the chest. Sometimes, the cause is unknown.
Pneumothorax may be “closed” or “open”. In a “closed” pneumothorax, there is no opening through the chest wall, and the air accumulation is coming from damage to the lower respiratory tract (trachea, bronchi, lungs). In an “open” pneumothorax, air enters the space around the lungs through the chest wall.
What are the types of pneumothorax?
Pneumothorax can occur in three different ways.
- Traumatic pneumothorax: Damage to the chest wall or lung caused by injury such as being hit by a car or bitten by a dog.
- Iatrogenic pneumothorax: Damage to the lower respiratory tract (including trachea, bronchi, and lungs) or body wall caused by a veterinary procedure.
- Spontaneous pneumothorax: Lung tissue becomes extensively damaged by disease, resulting in an air leak.
What is traumatic pneumothorax?
With a traumatic pneumothorax, there is typically evidence of recent trauma. With obvious damage to the chest wall, it is straightforward to diagnose an open pneumothorax. These dogs present with rapid breathing, difficulty breathing, and they may be in respiratory distress.
Dogs experiencing respiratory distress associated with pneumothorax often stand with their elbows pushed away from their bodies to increase their lung capacity. They may exhibit “abdominal breathing”, in which the origin of each breath seems to be the abdominal wall moving rather than the chest expanding. Pneumothorax patients may also have a higher-than-normal heart rate.
Trauma patients with pneumothorax may also have pale or bluish mucous membranes, they may be in shock, and they may have air trapped under the skin – a condition called “subcutaneous emphysema” that feels like “crackling” when you pet them over the affected areas.
The causes of traumatic pneumothorax can be quite varied and include:
- Blunt trauma (like being kicked by a horse or hit by a car)
- Chest injuries that penetrate into the chest cavity
- Surgical incision into the chest (a planned and controlled trauma to the chest cavity)
- Perforation of the esophagus on its way to the stomach
- Trauma to the windpipe (trachea)
- Lung disease
- Foreign body migration (like a grass awn migrating through the tissues of the body)
What is spontaneous pneumothorax?
In a spontaneous pneumothorax, air leaks from the lungs or the large air passages and accumulates in the chest space outside the lungs, in the absence of any trauma. Any spontaneous pneumothorax would be considered closed, because there are no defects, injuries, or openings in the chest wall. Spontaneous pneumothorax is more common in large, deep-chested dogs. The Siberian husky may be unusually susceptible.
Dogs that develop a spontaneous pneumothorax may or may not have previous signs of lung disease. The condition may have a slow, progressive onset, but what typically occurs is a sudden loss of the ability to compensate for the air that is outside the lungs and preventing the lungs from expanding properly for breathing. The symptoms of spontaneous pneumothorax are the same as those of traumatic pneumothorax; however, the causes are quite different.
"The causes of spontaneous pneumothorax originate in the lungs."
The causes of spontaneous pneumothorax originate in the lungs. In the absence of underlying lung disease, this condition is called primary spontaneous pneumothorax. The most common cause is a condition in which the air spaces in the lungs become dilated, and the air can get in (on inhalation) but cannot get out (on exhalation). This is called “bullous emphysema”.
Secondary spontaneous pneumothorax is caused by underlying lung disease such as lung cancer, lung abscesses, heartworm disease, inflammatory airway disease, allergic bronchitis, tracheal rupture, foreign body migration, severe pneumonia, lung worms or flukes, or lung nodules caused by fungal infection.
Tension pneumothorax
Tension pneumothorax most often occurs when patients are intubated (have a breathing tube inserted during general anesthesia or use of a ventilator). If the pressure of the ventilation is too great, the lung can rupture (burst). The resulting flap-like defect can act like a one-way valve, allowing air to accumulate outside of the lung and within the chest cavity.
Less common causes of tension pneumothorax include trauma (blunt force or penetrating) and spontaneous pneumothorax resulting from the effects of regular breathing on a lung compromised by disease.
How is pneumothorax treated?
Definitive treatment of pneumothorax depends on the underlying cause, but there are commonalities across the spectrum of patients who develop this condition. Most dogs require hospitalization until the air accumulation within the chest cavity has stopped or stabilized. If the dog presents in respiratory distress, then part of the treatment involves extracting the air from inside the chest cavity to allow the lungs to expand. Oxygen therapy is typically provided until the dog is stable.
In traumatic pneumothorax, or for dogs requiring surgery to resolve the underlying issue that led to the pneumothorax, it is important that effective pain relief be provided. If there is a significant defect in the chest wall, surgery will be required once the dog is stable and receiving adequate oxygen into the tissues. Removal of part or all of a lung may be necessary if there are localized lesions, masses, etc. Any traumatic lacerations of the lung may be sutured closed.
A closed traumatic pneumothorax may not require any intervention beyond stabilization. Sometimes, a chest tube is required to allow the removal of air that accumulates in the chest cavity. If a chest tube is placed, it is important that the dog not be allowed to dislodge it. Most dogs require strict rest for at least a week (and often longer) following resolution of pneumothorax, to minimize the chance of recurrence.
What sorts of complications can arise from having a pneumothorax?
It is possible for pneumothorax to cause a fatal cardiovascular event due to overly low oxygen levels in the blood. Another important potential complication is recurrence. It is important to monitor the dog’s breathing rate, as an increased breathing rate may suggest a recurrence. Follow-up X-rays may be required, as may additional measurements of blood oxygen levels.
What is the expected recovery and long-term outlook after suffering a pneumothorax?
For traumatic pneumothorax, if the chest trauma is not too severe and if treatment goes according to plan, the expectation is for a full recovery. If the chest trauma is severe, it is possible for the dog to decline despite all interventions and emergency efforts. If there is bleeding into the lungs or bruising of the heart, these patients can deteriorate quickly.
The recovery and long-term outlook for a dog with spontaneous pneumothorax is more complicated, because it depends on the underlying cause. A well-identified, single, localized lesion that can be removed surgically provides a better outlook than if the underlying cause cannot be identified or if there is disease throughout the lungs.
While pneumothorax is a serious condition, it is important to note that, with advances in diagnostic and treatment options, these dogs can often be treated with a successful outcome.
