An Overview of Hypercapnia

How this gas can be a problem for you

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Hypercapnia is excess carbon dioxide (CO2) buildup in your body. The condition, also described as hypercapnia, hypercarbia, or carbon dioxide retention, can cause effects such as headaches, dizziness, and fatigue, as well as serious complications such as seizures or loss of consciousness.

Hypercapnia may develop as a complication of chronic lung diseases such as COPD, bronchiectasis, emphysema, interstitial lung disease, and cystic fibrosis, as well as some neurological and muscle diseases.

Alveoli in the lungs
Dorling Kindersley / Getty Images

Your CO2 level can be measured with a blood sample, and you may also need other diagnostic tests to identify the cause of your hypercapnia. Typically, this problem requires intervention with medication and/or assistance with breathing, such as a breathing mask or a mechanical ventilator.


Often, hypercapnia does not cause obvious effects, and most people do not notice or complain of symptoms.

Common symptoms of hypercapnia, if they do occur, include:

  • Fatigue 
  • An inability to concentrate or think clearly
  • Headaches
  • Flushing
  • Dizziness
  • Dyspnea (shortness of breath)
  • Tachypnea (rapid breathing)
  • Increased blood pressure

Because these effects are so vague, you might not realize that they are caused by hypercapnia. Some people who have lung disease measure their own oxygen levels at home with a pulse oximeter, but this device cannot detect hypercapnia.

Your CO2 level may be too high even if your oxygen level is normal.

When you have a chronic respiratory disease, your CO2 level may be slightly elevated or may increase gradually over the course of years as your disease progresses. You can also experience sudden bouts of hypercapnia during exacerbations of a pulmonary condition.

The level of CO2 in your blood can increase abruptly if you develop a severe lung infection, especially if you already have a chronic lung disease like chronic obstructive pulmonary disease (COPD).


Severe hypercapnia can cause noticeable and distressing effects. You may experience sudden respiratory failure, which can lead to a coma and may even be fatal.

Serious, urgent symptoms of hypercapnia can include:

  • Paranoia, depression, and confusion
  • Muscle twitches
  • Seizures
  • Palpitations (a feeling that you are having a rapid heart rate)
  • Panic, or a feeling of impending doom
  • Dilation (widening) of superficial veins in the skin
  • Papilledema (swelling of the optic nerve)

Seek emergency medical care if you experience any of these.


CO2 is a gas that is produced as a normal byproduct of your body’s energy production. This gas diffuses into your bloodstream so that it can be exhaled from your lungs. In a healthy person, the typical respiratory rate and depth adequately exhale CO2 from the body.

The amount of CO2 in your blood is carefully regulated. When CO2 levels become elevated, special receptors in your brain detect the increased blood level. These receptors send messages to your lungs to make you breathe more deeply and/or at a faster rate until your CO2 reaches a normal level.

Due to the mechanisms that regulate the body’s CO2 level, it is rare for someone who is healthy to develop medically significant hypercapnia.

When hypercapnia occurs, in general, it can result from excess CO2 production or reduced CO2 exhalation from the lungs. There are health issues that may be at the root of this, and a number of risk factors increase the odds of it occurring.

Metabolic Changes

Illnesses, infections, and severe trauma can cause an alteration in the body’s metabolism, resulting in excess CO2 production. If your breathing can’t catch up with your need to exhale CO2 from your body, you can develop an elevated blood CO2 level.

Causes of excess CO2 production include:

  • Severe illness, infection, or trauma
  • Hypothermia (too-low body temperature)
  • Scuba diving (due to pressure changes)
  • Improper settings on a ventilator

Lung Disease

Lung disease can interfere with CO2 diffusion. A situation called ventilation/perfusion (V/Q) mismatch occurs when you have severe lung damage that prevents the flow of blood and/or air in your lungs. This interferes with CO2 diffusion and causes the gas to build up in your body.

Examples include:

  • COPD
  • Emphysema
  • Interstitial lung disease (including pulmonary fibrosis)
  • Cystic fibrosis
  • Bronchiectasis

COPD is a major cause of hypercapnia, though not everyone who has COPD—even severe or end-stage disease—will develop this problem.

Muscle Weakness

Neuromuscular diseases such as amyotrophic lateral sclerosis (ALS) and muscular dystrophy can make it a struggle to breathe, resulting in a buildup of blood CO2 levels. Myasthenia gravis is another neuromuscular cause of hypercapnia.

Central Hypoventilation

Conditions that impair your brain’s respiratory regulation may result in CO2 accumulation in your blood. Your respiratory control can be impaired by an overdose of narcotics, a stroke, or a degenerative brain condition, such as:


The diagnosis of hypercapnia begins with a careful history and physical examination. Your medical team may be closely monitoring you for signs of sudden hypercapnia such as when you have a serious illness or during surgery.

Other times, your team may have been periodically monitoring your CO2 level for months or even years (if you have chronic pulmonary fibrosis, for example).

If you are at risk for and/or have signs of hypercapnia, you will likely need to have a blood test that measures your CO2 level. An arterial blood gas (ABG) test measures your blood oxygen, CO2, bicarbonate, and pH.

Typically, blood tests use blood samples taken from a vein. An ABG test requires a sample of blood from your artery.

Hypercapnia is usually diagnosed when CO2 pressure measures at 45 mm Hg or above.

You may need to have your CO2 level monitored on a regularly scheduled basis, such as every few hours while receiving medical treatment in the hospital intensive care unit or every few minutes during surgery.

Diagnostic Tests

In addition to your arterial blood gas, your medical team will also work to identify the cause of your hypercapnia. You might need a number of tests to help in the diagnosis of your illness.

These may include:

  • Pulse oximetry: Your oxygen level can read as normal even when you have hypercapnia, but pulse oximetry is a noninvasive test that can be used to monitor sudden changes.
  • Blood tests: An increase in carbon dioxide in the blood also causes blood acidosis (lowering of the pH of the blood). You can develop respiratory acidosis due to a lung problem or metabolic acidosis due to a medical illness.
  • Pulmonary function tests (PFTs): Several measures of your respiratory function can help your medical team assess your lung function. These include your vital capacity (the maximum amount of air that can be inhaled or exhaled from the lung) and forced expiratory volume in one second (FEV1).
  • Imaging tests: Tests such as a chest X-ray and chest computerized tomography (CT) can help evaluate the severity of pulmonary conditions like emphysema and pneumonia. If your healthcare provider is concerned about central hypoventilation, you may need a brain imaging test, such as a magnetic resonance imaging (MRI) test.


Hypercapnia can lead to respiratory failure and coma if left untreated. The treatment of this condition involves improving ventilation so that you can get rid of the excess CO2. The type of treatment that you will need depends on the severity of your condition.

Treatment options may include:

  • Noninvasive ventilation: Noninvasive ventilation provides ventilatory support through the upper airways. A tightly fitted mask is placed on your face or nose. The mask is connected to a machine that delivers gentle air pressure and oxygen from a flow generator, though you can still breathe on your own.
  • Intubation: Intubation is an invasive process. An endotracheal tube is placed in your mouth and down into your airway. You are not able to voluntarily breathe or speak while you are intubated. You may need this type of respiratory assistance temporarily while a severe medical illness is treated.
  • Mechanical ventilation: When you are intubated, the tube that is placed in your mouth is hooked up to a mechanical ventilator that takes over your breathing for you.

In addition to managing your CO2 level, your medical team will also need to provide medical care for the treatment of the underlying cause of your condition. This can involve therapies such as bronchodilators for COPD or antibiotics for an infection.

A Word From Verywell

Typically, you think about your oxygen level when you have pulmonary disease. But your CO2 level can be affected by respiratory conditions too. Hypercapnia can also develop due to muscle disease and neurological disease.

If you are at risk for hypercapnia, it is important that you know the signs of this condition so that you can get medical attention if you start to develop a high blood CO2 level.

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9 Sources
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