What Is Hypercapnia?

Hypercapnia is an excessive level of carbon dioxide (CO2) in the blood. The build-up of CO2 can happen for many reasons and cause mild to severe symptoms.

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Hypercapnia is a term used to describe too much carbon dioxide (CO2) in the bloodstream. It occurs when your lungs cannot eliminate enough CO2 through breathing, leading to symptoms such as shortness of breath, headaches, confusion, and drowsiness. 

Conditions associated with decreased lung function, such as chronic obstructive pulmonary disease (COPD) or asthma, commonly cause hypercapnia. Metabolic changes, certain medications, and illness can also lead to hypercapnia. 

While hypercapnia can be dangerous, there are treatment options and ways to prevent it from happening in the first place. 

What Causes Hypercapnia?

The body produces CO2 as a waste product of metabolism, or the body's conversion or use of energy. CO2 is normally eliminated through the lungs when you breathe. An imbalance between the amount of CO2 the body produces and the amount of CO2 the lungs eliminate causes hypercapnia, also called hypercarbia.   

Normally when CO2 levels in the blood increase, your body responds by sending signals to your brain to make you breathe more deeply or rapidly until your CO2 levels are within the normal range. Certain health conditions can make it difficult to eliminate sufficient amounts of CO2, leading to hypercapnia. 

Lung Diseases 

Conditions that affect the respiratory system can impair the body’s ability to eliminate CO2 effectively, causing hypercapnia. Lung diseases and breathing disorders associated with an increased risk of hypercapnia include: 

Metabolic Changes and Disorders

Certain metabolic disorders, as well as infections, illness, or trauma that cause the body to produce too much CO2, can trigger changes to the body’s metabolism. If your breathing does not effectively eliminate the excess CO2, you can develop hypercapnia. 

Metabolic changes and disorders that cause the overproduction of CO2 include: 

  • Scuba diving
  • Carb-heavy meals 
  • Thyroid disorders 
  • Kidney failure 
  • Sepsis 
  • Increased use of steroids
  • Fever
  • Exercise

Neuromuscular Problems 

Neuromuscular problems and disorders that affect the muscles used for breathing can cause hypercapnia. These disorders can make breathing or forcefully exhaling difficult, which can lead to an accumulation of CO2 in the lungs and bloodstream.

Some examples of neuromuscular diseases that can lead to hypercapnia include:

  • Muscular dystrophy
  • Amyotrophic lateral sclerosis (ALS) 
  • Guillain-Barré syndrome
  • Cervical spine (neck) injury
  • Multiple sclerosis 

Medications and Toxins

Certain medications and toxins can cause slow breathing (respiratory depression) or affect the body’s ability to effectively use oxygen, leading to the build-up of CO2 in the lungs. 

Taking too many sedatives, such as benzodiazepine depressants or tricyclic antidepressants, can cause hypercapnia.

Toxins from the following can also cause hypercapnia:

  • Botulism 
  • Tetanus 
  • Shellfish poisoning 


Hypercapnia symptoms can vary depending on whether the development is acute or chronic.


Acute hypercapnia is the sudden increase in the levels of CO2 in the blood. Usually it occurs in response to a specific event or condition that causes an imbalance in the body’s ability to eliminate CO2, such as an asthma attack, an overdose of medication that slows down breathing, or a respiratory infection. Symptoms of acute hypercapnia include:

  • Inability to focus 
  • Shortness of breath
  • Dizziness 
  • Lethargy or fatigue 
  • Headache
  • Confusion 
  • Nausea
  • Flushed skin 


Chronic hypercapnia is when CO2 levels gradually increase over time, usually due to an underlying lung or heart disease, such as COPD or heart failure. These conditions can reduce the lungs’ ability to eliminate CO2. Symptoms may be less severe and may not be noticed until the condition has progressed. 

Symptoms of mild hypercapnia include:

  • Fatigue
  • Drowsiness
  • Irritability
  • Lightheadedness
  • Poor concentration
  • Increased heart rate

Symptoms of a more severe case of hypercapnia include:

  • Confusion, depression, or paranoia 
  • Seizure
  • Hyperventilation 
  • Heart palpitations
  • Fainting
  • Muscle twitches
  • Panic attack 
  • Swelling of the optic nerve (papilledema) 
  • Respiratory failure
  • Coma


Hypercapnia is diagnosed through medical history, physical examination, and laboratory tests.

If you have symptoms of hypercapnia, your healthcare provider will take a thorough medical history, including information about your symptoms, any health conditions you have, and the medications you are currently taking. Your healthcare provider will also perform a physical exam to evaluate your breathing rate, listen to your heart rate, and look for any signs of respiratory distress such as wheezing or sweating.

A blood gas test is the standard diagnostic test for hypercapnia. A blood sample will be taken from an artery or vein and sent to the laboratory to measure CO2, oxygen, and other gasses in the blood. 

Hypercapnia is diagnosed if the partial pressure of CO2 (PaCO2) is higher than 42mm of mercury.

Additional tests may also be performed to help identify the underlying cause of hypercapnia, such as: 

  • Complete blood panel: A blood test to check for anemia 
  • Metabolic panel: A blood test to check many body functions and processes, including metabolism and liver health 
  • Lung function tests: A variety of tests that measure how well the lungs work 
  • Chest X-ray: Imaging scan to look for lung abnormalities or diseases 
  • Chest computed tomography (CT) scan: Imaging scan that creates detailed images to look for lung abnormalities and diseases 
  • Electrocardiogram (ECG) or electromyography (EMG): Measures heart, muscle, and brain activity to check for nervous system disorders and neuromuscular diseases 
  • Sleep study: Overnight test that measures brain waves, heart rate, breathing, and oxygen level in the blood during sleep and helps diagnose sleep disorders like sleep apnea)


Hypercapnia can sometimes lead to complications. Acute hypercapnia can lead to short-term consequences, such as: 

  • Unconsciousness 
  • Confusion
  • Paranoia
  • Panic attacks
  • Irregular heartbeat 
  • Cardiovascular collapse 

In people with chronic hypercapnia, long-term complications can occur, including:

  • Low oxygen levels in the blood (hypoxemia) and tissue death 
  • Irregular heartbeat 
  • Cognitive impairment 
  • Muscle loss 
  • Depression

Respiratory failure from hypercapnia can occur when the amount of carbon dioxide in the blood is between 45-60mm of mercury. 

Hypercapnia can also worsen existing medical conditions, such as COPD, making managing these conditions more challenging.

How Is Hypercapnia Treated?

Hypercapnia is initially treated with oxygen therapy to promote ventilation and help rid the body of excess CO2. With this therapy, additional oxygen is supplied to the body through a face mask or nasal cannula to help reduce the level of CO2 in the blood.

Other treatment options vary, and the specific treatment chosen depends on the severity of the condition. Common hypercapnia treatments include:

  • Non-invasive mechanical ventilation (NIV): NIV involves using a mask or a mouthpiece to deliver air or a mixture of air and oxygen. The pressure provided by the mask or mouthpiece helps open up the airways and make breathing easier.
  • Invasive mechanical ventilation (IMV): IMV involves using a ventilator machine to take over the work of breathing and balancing blood gasses. A tube is placed down the throat (intubation). This treatment is used for severe cases of hypercapnia. 
  • Medications: Certain medications, such as bronchodilators, can help open up the airways and make breathing easier. Corticosteroids can also be used to reduce inflammation in the lungs.
  • Pulmonary rehab: Pulmonary rehab is usually a combination of exercise training, education, and breathing techniques to help improve lung function and overall physical fitness. 

Underlying conditions that cause hypercapnia require ongoing treatment to manage the condition and prevent future hypercapnic episodes.

Risk Factors

Anyone can experience hypercapnia, but certain risk factors can increase the likelihood of developing the condition:

  • Smoking 
  • Exposure to fumes or chemicals that can damage the lungs
  • Obesity 
  • Use of opioids or sedatives
  • Older age 
  • Excessive alcohol consumption
  • Chest or lung injury 


Preventing hypercapnia can be challenging, as some risk factors are out of your control. However, if you have a condition that may contribute to the development of hypercapnia, there are things you can do to reduce your risk: 

  • Quit smoking: Smoking can lead to lung damage and chronic lung conditions like COPD—a leading cause of hypercapnia. Quitting smoking can help improve lung function and help prevent or slow the progression of COPD and other lung diseases. 
  • Maintain a healthy weight: Hypercapnia and other breathing troubles are more common in people with obesity.
  • Manage underlying conditions: If you have a condition that increases the risk of hypercapnia, it is vital to manage it properly and follow your healthcare provider’s treatment recommendations. This includes taking medications as prescribed, avoiding triggers, and having regular check-ups.
  • Be aware of medication side effects: Certain medications can slow breathing and lead to hypercapnia. Take your medicines as prescribed, and talk to your healthcare provider if you have concerns about potential side effects.
  • Avoid triggers: If you have asthma or COPD, it's important to avoid triggers that can cause an asthma attack or make it more difficult to breathe, such as dust, pollen, or cigarette smoke.

A Quick Review

Hypercapnia, or a buildup of carbon dioxide (CO2) in the blood, occurs when the body cannot effectively eliminate CO2. Lung diseases, sleep apnea, neuromuscular disorders, metabolic changes/conditions, and certain drugs can cause hypercapnia. Symptoms can range from mild to severe, including shortness of breath, headache, confusion, and fatigue. 

When symptoms are severe, hypercapnia is a medical emergency that requires prompt treatment to prevent complications. Hypercapnia can be diagnosed through a combination of medical history, physical examination, and laboratory tests. Treatment options include oxygen therapy, mechanical ventilation, medications, and treating and managing the underlying cause. 

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