An Overview of Hypercapnia

How This Gas Can Be a Problem for You

Over time and with practice, many people learn how to stay alert to their body's signals, ask their primary caregiver good questions, and become their own best advocate.

These are valuable skills to have with any condition, but particularly with one like hypercapnia. This is the name for having too much carbon dioxide (CO2) in the blood.

Some people don't even realize they have the condition. It may wake them up in the middle of the night. But all they do is roll over and go back to sleep. However, severe hypercapnia can be a life-threatening health crisis.

This article explains the difference in symptoms between mild and severe hypercapnia, some of the possible underlying causes, and how the condition is treated.

Alveoli in the lungs
Dorling Kindersley / Getty Images

How Your Lungs Work

The respiratory system is simple and complex at the same time: As you inhale, air enters your lungs and then oxygen moves into the blood.

Once this mission is accomplished, you exhale the waste product carbon dioxide. This simple process is called gas exchange.

The process can get complex, and fast, when not enough oxygen enters the lungs. The bigger threat is when not enough carbon dioxide is exhaled and the body's CO2 level spikes as a result.

This state is known as hypercapnia—sometimes called hypercarbia or carbon dioxide retention.

There are many reasons why this imbalance can occur.

Mild Hypercapnia, Mild Symptoms

Many people are unaware that they have mild hypercapnia. When you consider the common, everyday nature of the symptoms, you might understand why. They can include:

  • Dizziness
  • Fatigue 
  • Flushing
  • Headaches
  • Inability to concentrate or think clearly
  • Increased blood pressure
  • Muscle twitches
  • Rapid breathing (tachypnea)
  • Shortness of breath (dyspnea)

Consider the last symptom and how someone fast asleep could suddenly awake, turn over, and return to their normal breathing pattern.

This happens almost seamlessly, because 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 faster until your CO2 reaches a normal level.

Like a well-oiled, intuitive machine, the body has automatically taken care of itself; it has returned the CO2 level to a healthy level with no medical attention necessary—perhaps ever.

It can be a very different story with severe hypercapnia. An underlying health condition is often the culprit, affecting both breathing and the blood.

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

Severe Hypercapnia, Severe Complications

Severe hypercapnia can cause noticeable and distressing effects. Unlike mild hypercapnia, the body is incapable of restoring CO2 balance, which can lead to urgent symptoms:

  • Acute paranoia, depression, or confusion
  • Coma
  • Dilation (widening) of blood vessels in the skin
  • Fainting
  • Hyperventilating
  • Panic attack
  • Respiratory failure
  • Seizure
  • Swelling of the optic nerve (papilledema)

Severe cases of hypercapnia can lead to respiratory failure and coma if left untreated. So call 911 if you experience any of these symptoms.


Hypercapnia results from excess CO2 production or reduced CO2 exhalation from the lungs. Some health issues may be at the root of these dynamics, and a number of risk factors may increase the odds of the condition developing.

For example, hypercapnia may stem from chronic lung diseases such as COPD, bronchiectasis, emphysema, interstitial lung disease, and cystic fibrosis. It can also stem from some neurological and muscle diseases.

It's rare for someone who is healthy to develop severe (also known as "medically significant") hypercapnia. But four types of health issues can trigger the condition.

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

Onset of Lung Disease

Lung disease can interfere with CO2 removal. 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.

Certain chronic conditions can cause CO2 gas to build up in the body:

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

COPD is a major cause of hypercapnia. But even people with severe or end-stage COPD may not develop hypercapnia.

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.

Brain Disorders

Conditions that impair your brain’s ability to regulate breathing may result in CO2 accumulation in your blood (central hypoventilation). Your respiratory control can be impaired by an overdose of narcotics, a stroke, or a degenerative brain condition such as:


Often, the symptoms of mild hypercapnia are simple enough for an experienced healthcare provider to address. They are worth monitoring, particularly if they linger or get worse.

Severe hypercapnia requires a more assertive approach. Efforts usually focus on a search for the underlying trigger. And the search begins with a careful history and physical examination.

You will likely need 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.

You may also need other diagnostic tests. In the meantime, you may require intervention with medication and/or assistance with breathing from a breathing mask or mechanical ventilator.

Hypercapnia is usually diagnosed when CO2 pressure measures at 45 mm Hg (millimeters of mercury) or above.

Diagnostic Tests

Aside from blood tests, certain go-tests include:

  • Imaging tests: Tests such as a chest X-ray and chest computerized tomography (CT) scan can help evaluate the severity of pulmonary conditions like emphysema and pneumonia. If your healthcare provider thinks the cause may be related to the brain, you may need a brain imaging test, such as a magnetic resonance imaging (MRI).
  • Pulmonary function tests (PFTs): Several measures of your respiratory function can help your healthcare provider 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 1 second (FEV1). This test measures how much air you can forcefully exhale in 1 second.
  • 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.


Treating hypercapnia focuses on improving ventilation so that you can get rid of excess CO2. The type of treatment used depends on the severity of the condition.

The options include:

  • Intubation requires that an endotracheal tube be placed in your mouth and down into your airway. You are unable to breathe or speak while you are intubated. You may need this type of respiratory assistance temporarily while a severe medical illness is being treated.
  • Mechanical ventilation involves the use of a mechanical ventilator that takes over the act of breathing for you.
  • Noninvasive ventilation: Noninvasive ventilation provides breathing support through the upper airways. A tightly fitted mask is placed over 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.
  • Oxygen therapy gives you freedom of movement while you're being treated for hypercapnia. You must wear a device that resembles an over-the-shoulder purse or backpack with a tube (cannula) that delivers oxygen into your nose.
  • Pulmonary rehab is another treatment option. It can vary greatly from one patient to another but can include a mix of breathing exercises, physical exercises, and diet and nutrition consultations.


Mild hypercapnia can be hard to spot. Having too much carbon dioxide in the body can cause nonspecific symptoms like headache, fatigue, and muscle twitches. Often, it clears up quickly on its own.

With severe hypercapnia, though, the body can't restore CO2 balance and the symptoms are more serious. An underlying health condition usually triggers hypercapnia, and the sooner it's identified, the sooner you can get treatment.

A Word From Verywell

It's common for your oxygen level to remain top-of-mind 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.

The bottom line is: If you're at risk for hypercapnia, it's crucial to learn about the condition's red flags so that you can get proper medical supervision. Mild symptoms can become severe symptoms, and these can be life-threatening.

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9 Sources
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