When blood pools in your pleural cavity, the space between the chest wall and the lungs, it’s called a hemothorax. This buildup of blood can cause your lung to collapse.

Hemothorax is when blood collects between your chest wall and your lungs. This area where blood can pool is known as the pleural cavity. The buildup of the volume of blood in this space can eventually cause your lung to collapse as the blood pushes on the outside of the lung.

The pooling of blood in your chest can have numerous causes. It’s most common after major chest injuries or surgeries that include opening your chest wall, especially heart or lung surgery. Certain conditions that cause your blood not to clot properly can also cause hemothorax.

Hemothorax can be caused by many of the same things that cause pneumothorax. Pneumothorax happens when too much air gets between your chest wall and lungs. This puts too much pressure on your lung and causes the lung or part of the lung to collapse.

You may not immediately notice symptoms of hemothorax. See your doctor right away if you believe you might have this condition.

The most common symptoms of hemothorax include:

  • pain or feeling of heaviness in your chest
  • feeling anxious or nervous
  • dyspnea, or having trouble breathing
  • breathing quickly
  • abnormally fast heartbeat
  • breaking out in cold sweats
  • skin turning pale
  • high fever over 100°F (38°C)

If your heart is racing and you’re having trouble breathing, go to an emergency room right away to be checked for hemothorax or other conditions that may be causing these symptoms.

The most common cause of hemothorax is a major injury to your chest. This is known as a blunt force trauma injury. This can happen when your chest experiences a sudden and intense impact. Examples include falling hard on the front of your body or getting in a car accident and part of the vehicle — like the steering wheel or a deployed air bag — hits the chest extremely hard.

These injuries can damage your chest wall, your lungs, and major blood vessels around your chest. This allows blood to leak into your chest cavity and put pressure on your lungs. Getting cut or stabbed in the chest can also cause blood to leak into the chest cavity and cause hemothorax.

Hemothorax also commonly happens as a complication of a major heart or lung surgery that requires a surgeon to open the chest wall. Blood can leak into the chest cavity if the blood doesn’t clot properly after the surgeon closes the incisions, or if an organ or vessel is cut open and leaks blood.

Other possible causes of hemothorax include:

  • blood not clotting properly and leaking into the chest cavity
  • cancer in the lungs
  • fluid and cancer around the lungs, called malignant pleural effusion
  • cancerous tumors in your chest wall
  • large vein torn open when a catheter is inserted while you’re in the hospital
  • tissue around your lungs dying, called pulmonary infarction
  • Ehlers-Danlos syndrome (EDS) type 4, a condition that affects your connective tissues

In rare cases, especially outside of the United States and other developed countries, hemothorax can be caused by tuberculosis (TB).

Hemothorax can also happen without warning during a pregnancy or after you’ve given birth. This is known as spontaneous hemothorax. It doesn’t always have an identifiable cause.

If you go to the emergency room for hemothorax, your doctor or emergency medical staff will use emergency tools, such as a ventilator with a tube inserted through your nose into your windpipe, to support your breathing and make sure you’re getting enough oxygen.

The most important treatment for hemothorax is draining the blood out of your chest cavity. Your doctor will likely put a tube through your chest muscles and tissues, through your ribs, and into your chest cavity to drain any pooled blood, fluid, or air. This is called a thoracentesis or thoracostomy.

The tube may remain in your chest for several days if your lung has collapsed so that it can expand again.

If the bleeding continues even as the tube drains the blood, you may need chest surgery to treat the cause of the bleeding. Chest surgery is also known as thoracotomy.

The type of thoracotomy needed is based on which part of your chest or organs your surgeon needs to operate on. After your surgeon finishes the operation, a tube will remain inserted in your chest to drain any remaining blood or fluid.

Your doctor may take several types of imaging tests of your chest and lungs to see what’s causing the bleeding, especially if you’ve had a major chest injury.

CT scans can show your doctor the structures around your chest and lungs so they can see any abnormalities. Your doctor may also take X-rays if you’ve broken any bones or been injured anywhere else around your chest or abdomen area in case other treatment needs to be provided.

If your doctor suspects that an underlying condition — such as cancer, tuberculosis, or EDS — is causing your hemothorax, they may recommend further blood or imaging tests to properly diagnose and treat that condition.

Losing a lot of blood from this condition can cause your body to go into shock because of the lack of blood and oxygen being pumped throughout your body to your organs.

Shock caused by blood loss is called hypovolemic shock. Going into hypovolemic shock can cause long-term or permanent damage to your organs, including your heart, lungs, and brain.

Blood getting into your chest cavity can infect fluid in the area around your lungs. This type of infection is known as empyema. An untreated empyema infection can lead to sepsis, which happens when inflammation occurs throughout your body. Sepsis can be fatal if not treated quickly.

A collapsed lung, if untreated, can cause you to stop breathing. This is known as respiratory failure. It can be fatal unless you’re able to get emergency medical help.

See your doctor as soon as possible after a serious chest injury and if you have trouble breathing for longer than a minute. Call your doctor if you develop any of the symptoms listed above.

Hemothorax is a serious condition. However, hemothorax won’t cause any long-term damage if it’s diagnosed and treated early.