Pneumothorax

Definitions & Key takeaways

A pneumothorax refers to an abnormal collection of air or gas in the pleural space that causes a loss of negative pressure. Like pleural effusion (liquid buildup in that space), pneumothorax may interfere with normal breathing. Pneumothorax can either be traumatic, or spontaneous. Traumatic pneumothorax occurs due to an injury to the chest, such as a broken rib or puncture wound. On the other hand, spontaneous pneumothorax can happen without an apparent cause. It is commonly seen in patients with lung diseases such as COPD, cystic fibrosis, asthma, smokers, and people with Marfan syndrome. Symptoms of pneumothorax can include chest pain, shortness of breath, and difficulty breathing. The diagnosis is typically made with a chest X-ray or CT scan. Treatment for a pneumothorax may require a chest tube to remove the air or gas and re-expand the lung.

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With pneumothorax, pneumo refers to air and thorax means chest, so a pneumothorax is when there is air in the chest; more specifically air in the space between the lungs and chest wall – called the pleural space.
The pleural space lies between the parietal pleura, which is stuck to the chest wall, and the visceral pleura, which is stuck to the lungs.
The pleural space normally contains a lubricating fluid that helps reduce friction as the lungs expand and contract. Pressure within the pleural space is established by two main opposing forces.
One is the muscle tension of the diaphragm and chest wall which contract and expand the thoracic cavity outwards, and the other is the elastic recoil of the lungs, which try to pull the lungs inward.
The two pull on each other creating a balance between the forces that creates a slight vacuum in the pleural space. It results in the pleural space having a pressure of -5 centimeters of water relative to the pressure of 0 centimeters of water in both the thoracic cavity and the lungs.
A pneumothorax forms when the seal of the pleural space is punctured and air moves in from the outside, making the pressure in the pleural space equalize to 0 centimeters of water.
Since the negative pleural pressure is lost, the two opposing forces no longer pull on one another. As a result, the lungs simply pull inwards and collapse, and the chest wall simply springs outward a bit.
A collapsed lung limits how well it can exchange air, and can lead to a reduction in oxygen being brought into the body, and a build-up of carbon dioxide in the body because it can’t easily get released.
There are many types of pneumothorax. The first is a spontaneous pneumothorax which typically occurs when a bullae, which is an air pocket, forms on the surface of the lungs and breaks.
Bullae form when the alveoli, which are the terminal ends of the lung where gas exchange occurs, develop a tiny leak and air slowly seeps into the surrounding lung tissue.
Typically the alveoli heals up, otherwise it would itself lead to a pneumothorax. But the result is a bullae.
If the bullae breaks, it creates a large hole in the visceral pleura and air can go from the airway directly into the pleural space.
A primary spontaneous pneumothorax is one that develops in the absence of an underlying condition - most typically it’s in a thin, tall, adolescent male who is hold his breath, creating a lot of internal pressure.
A secondary spontaneous pneumothorax is one that develops in someone with an underlying lung disease, like Marfan’s syndrome, cystic fibrosis, emphysema, or lung cancer.
In contrast to a spontaneous pneumothorax, there’s also a traumatic pneumothorax which is when trauma like a gunshot wound or stab wound rips through the parietal pleura, allowing air to enter from the outside, directly into the pleural space.
Finally, there’s a tension pneumothorax which can develop similarly to a spontaneous pneumothorax or a tension pneumothorax - with the one difference being that it creates a one-way valve for air to flow into the pleural space.
In other words, air can enter, but cannot leave because there’s a flap of tissue that doesn’t allow air to go the other way.
Over time, air might build up, increasing the pressure, and it can start compressing the heart and lung making them less functional, and it can shift large structures like the trachea.
A tension pneumothorax that’s pressing on the heart is particularly dangerous because it can prevent the heart from filling up properly, reducing the cardiac output.
The main symptom of a pneumothorax is shortness of breath and chest pain. The extra air in the pleural space also changes sound transmission in the chest, so normal breath sounds become harder to hear with a stethoscope.
Also, when the chest is tapped, or percussed, the extra air in the pleural space makes the resonant sound get louder. Typically, an X-ray or CT is needed for diagnosis, and usually an outline of the collapsed lung can be seen with a distinct difference between lung tissue which is mostly black and the air in the pleural space which is completely black.
If there’s a tension pneumothorax, an Xray or CT might show displacement of chest structures, like the trachea away from the affected side - called tracheal deviation.
Often, if a spontaneous pneumothorax is small and not causing any shortness of breath, no treatment is required, and the pleura will heal over time.
But, with a larger pneumothorax that’s causing severe symptoms, or with a tension pneumothorax, the air needs to be removed.
Typically, this is done by inserting a needle or a chest tube, and providing an escape route for the air. Alright, as a quick recap - a pneumothorax is when there’s air in the pleural space and a loss of negative pressure.
That leads to lung collapse and chest wall expansion, which can cause shortness of breath and chest pain. A tension pneumothorax is when there’s a flap of tissue creating a one-way valve and it can allow pressure to build up.
Over time, that can press against nearby organs like the heart and can potentially affect cardiac output. In severe cases, a needle or chest tube can be used to decompress the air in the pleural space.