High Carbon Dioxide (CO2) in Blood: What to Know

High carbon dioxide (CO2) levels in the blood (hypercapnia) can be a life-threatening health crisis. It occurs when CO2 builds up in the bloodstream. This can be due to either an overproduction of CO2 or an inability to efficiently clear it from the body.

Hypercapnia can occur from an infection, illness, or trauma. People with chronic obstructive pulmonary disease (COPD), cystic fibrosis, and neuromuscular diseases are at increased risk of developing high CO2 levels in their blood.

Symptoms of high CO2 levels include dizziness, fatigue, and brain fog. It can also cause headaches, increased blood pressure, rapid breathing, or shortness of breath. Treatment can range from simple oxygen therapy to intubation and mechanical ventilation.

This article discusses high CO2 levels in the blood. It explains the causes and effects of hypercapnia and how it is diagnosed and treated.

What Is Hypercapnia?

Hypercapnia is a condition marked by excessive levels of carbon dioxide in the blood. Carbon dioxide (CO2) is a waste product of respiration.

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

Once you have inhaled oxygen, you exhale carbon dioxide. This process is called gas exchange.

Medical issues arise when not enough oxygen enters the lungs. However, problems can also occur if too little carbon dioxide is exhaled, which causes the body's CO2 level to spike.

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

What Are the Symptoms of Hypercapnia?

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

Hypercapnia symptoms can include:

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

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.

With severe hypercapnia, though, the symptoms and complications can become life-threatening.

Severe Symptoms

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
• Hyperventilation
• 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. Call 911 if you experience any of these symptoms.

What Causes High CO2 Levels?

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.

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.

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

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

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:

• Brainstem stroke
• Drug overdoses, such as with an opioid or benzodiazepine (used to treat anxiety)
• Nervous system disorders like encephalitis (a brain infection) or a large stroke

Genetic Factors

In rare cases, high CO2 blood levels can be due to a genetic condition known as alpha-1 antitrypsin (AAT) deficiency. 

AAT is a protein that is made in the liver and helps to protect the lungs from damage caused by smoking, pollution, and dust. People who are AAT deficient are at greater risk for lung diseases that can lead to hypercapnia. 

AAT deficiency occurs when a person inherits two mutated AAT genes—one from each parent. While it can occur in any ethnicity, it is more common among people of Northern European descent. 

Other Risk Factors

Anything that can damage your lungs can put you at risk for hypercapnia. This includes:

• Air pollution
• Asbestos exposure
• Radon exposure
• Smoking and exposure to second-hand smoke

How Is Hypercapnia Diagnosed?

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 cause, 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.

Diagnostic Tests

Aside from blood tests, certain go-to tests include:

• Imaging tests: A chest X-ray and chest computerized tomography (CT) scan can help to 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 magnetic resonance imaging (MRI).
• Pulmonary function tests (PFTs): Several measures of your respiratory function can help to 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.

How Is Hypercapnia Treated?

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:

• 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 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.

How Is Hypercapnia Prevented?

Hypercapnia can often be prevented by managing the underlying cause.

If you have a condition that puts you at risk for high CO2 levels, be sure to follow your treatment plan. Take your medications as prescribed, keep your follow-up appointments, and follow your healthcare provider's recommendations for monitoring.

Lifestyle changes can also help to prevent CO2 levels from getting too high. This includes:

• Getting regular exercise
• Losing weight if you are overweight
• Quitting smoking

Summary

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.