Hypercapnia (Hypercarbia)

Key Takeaways

• Hypercapnia, also called hypercarbia, refers to high levels of carbon dioxide in the blood.
• Mild hypercapnia symptoms include anxiety, shortness of breath, daytime sluggishness, sleeping for too long, and headaches.
• When hypercapnia becomes severe, it can cause confusion, paranoia, delirium, seizures, coma, and more.
• Hypercapnia may result from untreated sleep apnea, chronic obstructive pulmonary disease (COPD), excessive sleep, sedative overdose, and stroke.

Hypercapnia Definition

The official hypercapnia definition is elevated carbon dioxide levels in the blood. The severity of hypercapnia can vary from mild to serious, depending on how much carbon dioxide is in the blood and the rate at which levels rise. Hypercapnia is typically a sign of a medical issue that affects breathing, metabolism, or both. For example, severe hypercapnia is the primary symptom of acute respiratory failure.

The respiratory system consists of a person’s airway and lungs, which connect to the bloodstream to exchange the gases oxygen and carbon dioxide. When a person with healthy lung function breathes in, the respiratory system takes in oxygen and delivers it to every cell in the body. When a person breathes out, carbon dioxide gets removed from the body as a waste product. If either of these functions don't happen properly, it's considered an arterial blood gas issue.

Hypercapnia happens when something goes wrong in the process of breathing, and the body isn’t able to remove carbon dioxide from the bloodstream or it produces more carbon dioxide than normal.

Hypoxia vs. Hypercapnia

Hypoxemia describes when a person's blood oxygen levels are low, and hypoxia describes when not enough oxygen is being delivered to body tissues. A person with untreated sleep apnea may experience both low oxygen (hypoxemia and hypoxia) and high carbon dioxide (hypercapnia) at the same time. Because sleep apnea causes breathing to stop during sleep, there isn't enough oxygen inhaled or carbon dioxide exhaled to keep either level ideal.

Hypercapnia Symptoms

Mild hypercapnia may cause shortness of breath, sluggishness, or headaches, while severe cases can lead to more serious symptoms. Symptoms depend on how much carbon dioxide has collected in the bloodstream and how quickly its levels increased.

Mild to Moderate Hypercapnia Symptoms

Mild or moderate hypercapnia symptoms may include:

• Shortness of breath
• Anxiety
• Headaches
• Low energy
• Excessive daytime sleepiness
• Excessive, non-restorative sleep
• Nausea
• Vomiting

Severe or Acute Hypercapnia Symptoms

Severe or acute hypercapnia that develops quickly can lead to more serious symptoms such as:

• Delirium or severe confusion
• Paranoia
• Muscle tremors or jerks
• Dilated veins, which may cause flushed skin
• Drowsiness
• Depression
• Heart palpitations
• Fainting
• Seizures
• Coma
• Fast breathing
• Cardiac arrest

People with hypercapnia may experience a variety of other symptoms, depending on the underlying medical condition that caused the person’s carbon dioxide levels to increase.

Hypercapnia Causes

Some of the most common factors that can cause hypercapnia include chronic lung disease, sedative medications, and sleep apnea. A range of underlying medical issues related to respiratory health can also cause carbon dioxide levels in the blood to rise.

• Slow and shallow breathing: When a person’s breathing rate slows, known as hypoventilation, carbon dioxide can build up in the bloodstream. Sedatives, such as opiate painkillers, can slow breathing down.
• Reduced gas exchange in the lungs: Some people have defects in the respiratory system that make it harder to exchange oxygen for carbon dioxide. Medical experts refer to inhaled air that isn't part of gas exchange as “dead space.” Among people with hypercapnia, reduced gas exchange is usually due to cases of co-occurring chronic lung disease.
• Increased carbon dioxide production: Although less common, increased carbon dioxide production can happen with conditions that cause fever, like infections and sepsis.

Sleep Apnea and Hypercapnia

Sleep apnea is a sleep-related breathing disorder diagnosable with a simple at-home sleep test that can cause short lapses in a person’s breathing while they sleep, which may lead to hypercapnia if left untreated. There are two types of sleep apnea.

• Obstructive sleep apnea: Obstructive sleep apnea (OSA) is the most common form of sleep apnea and occurs when the upper airway becomes blocked during sleep.
• Central sleep apnea: Central sleep apnea (CAS) occurs when there’s an interruption in brain signals to the muscles that drive breathing during sleep.

Both types of sleep apnea interrupt breathing during sleep and can cause hypercapnia when not properly treated. Hypercapnia may be more likely to occur in people with sleep apnea when their body is under stress from an illness or after a surgery.

COPD and Hypercapnia

Chronic obstructive pulmonary disease (COPD) is a respiratory condition characterized by inflammation and damage to the lungs and air sacs which may lead to hypercapnia. The most common symptoms of COPD include:

• Coughing with mucus
• Shortness of breath
• Wheezing
• Low energy

COPD is usually caused by smoking tobacco but can also arise from exposure to toxins. As COPD progresses to a more advanced stage, it can become harder to breathe. The lungs can become less efficient at absorbing oxygen and removing carbon dioxide from the bloodstream, which may lead to hypercapnia.

Sedative Medications and Hypercapnia

Certain medications can impact breathing and lead to hypercapnia. Some substances that may cause hypercapnia include:

• Opiates
• Benzodiazepines
• Certain anesthetics
• Tricyclic antidepressants

Other Causes of Hypercapnia

Hypercapnia can also be caused by conditions that affect the respiratory muscles, the central nervous system and important metabolic processes. Other causes of hypercapnia include:

• Stroke
• Neuromuscular disorders like myasthenia gravis
• Kidney failure
• Dehydration or vomiting
• Diabetic ketoacidosis, a complication from diabetes

Complications of Untreated Hypercapnia

If hypercapnia remains untreated, it can become severe as carbon dioxide levels increase in the bloodstream. Severe hypercapnia can lead to multiple serious complications, such as an abnormal heart beat, cardiac arrest, coma, seizures, or even death.

Hypercapnia can be categorized as acute or chronic. With acute hypercapnia, symptoms can become severe and life-threatening quickly and require emergency medical attention. With chronic hypercapnia, blood carbon dioxide levels increase more slowly over time, and symptoms may be mild at first or appear later on in the process. However, chronic hypercapnia also requires medical attention.

How to Diagnose Hypercapnia

A doctor can diagnose hypercapnia with a blood test to check oxygen and carbon dioxide levels. To determine the severity and underlying cause of hypercapnia, the doctor may also take your medical history and order other bloodwork and imaging.

Respiratory System Assessment

First, a doctor may collect your medical history and ask you questions about your breathing and symptoms. They’ll likely also perform a physical examination. The medical history information and this exam can provide clues as to the causes and severity of hypercapnia.

Arterial Blood Gas Analysis

An arterial blood gas analysis (ABG) is a blood test taken to identify the amount of carbon dioxide found in the blood in a person's arteries. Hypercapnia is diagnosed if a measure called the CO2 tension is above 45 mmHg, which is described as a high partial pressure of carbon dioxide.

An ABG is the preferred blood test used to test for hypercapnia, because it tends to be more accurate than a venous blood gas analysis and can also be used to estimate blood oxygen levels. That said, sometimes drawing blood for an ABG feels painful for the patient or is difficult for a clinician, so a venous blood gas analysis is used, instead.

Venous Blood Gas Analysis

A venous blood gas analysis (VBG) is similar to an arterial blood gas analysis in the sense that both tests involve drawing blood to check its carbon dioxide levels. But, a VBG involves drawing blood from veins, whereas an ABG involves drawing blood from arteries. A VBG is considered less accurate and is generally only used when there's difficulty obtaining blood from an artery for an ABG.

Additional Tests

Additional medical testing may be needed to uncover the root cause of hypercapnia.

• Blood tests: In addition to an ABG or VBG, doctors may draw blood for a complete blood count to check for anemia, a metabolic panel to check for potential underlying metabolic causes, and a thyroid hormone test to check for an underlying thyroid disorder.
• Lung tests: Tests that measure lung capacity and breathing ability, like spirometry, provide insight on how well a person is breathing and may uncover a cause of hypercapnia.
• Chest imaging: Chest X-rays and computed tomography (CT) scans can identify factors that may negatively impact breathing, such as abnormal anatomy, pneumonia, or fluid in the lungs.
• Sleep study: An overnight, in-lab sleep study, called polysomnography, or a home sleep apnea test (HSAT) can help determine if a person has sleep apnea.
• Heart imaging: If a heart-related issue is thought to be involved, doctors may order imaging of the heart, including an echocardiogram, which involves a heart ultrasound.
• Nervous system tests: If doctors suspect a central nervous system problem or a neuromuscular problem is playing a role in a person's hypercapnia, they may order an electrocardiogram (ECG) and electromyogram (EMG), two tests that measure electrical activity in the body.

Hypercapnia Treatment

Treatment for hypercapnia depends on the severity and underlying cause. Initial treatments for hypercapnia generally focus on improving a person’s breathing to increase oxygen and reduce carbon dioxide levels in the blood. In acute hypercapnia, therapies may be given immediately, while a person is awake. In chronic hypercapnia, treatments are often used during sleep.

Bilevel Positive Airway Pressure (BiPAP) Therapy

Bilevel positive airway pressure (BiPAP) therapy can be used as an immediate form of non-invasive mechanical ventilation (NIV) to treat acute hypercapnia. BiPAP therapy involves a machine pushing air through a tube and mask into a person's airway at a higher pressure level during inhalation and a lower pressure level during exhalation. By improving breathing, BiPAP helps increase blood oxygen levels and lower carbon dioxide levels.

BiPAP therapy is also commonly used during sleep as a treatment for chronic hypercapnia in people with obesity hypoventilation syndrome (OHS), sleep apnea, or both disorders.

Continuous Positive Airway Pressure (CPAP) Therapy

Another form of PAP therapy, continuous positive airway pressure (CPAP) therapy, serves a similar purpose as BiPAP therapy when treating hypercapnia, which is to increase oxygen levels and reduce carbon dioxide levels. However, CPAP therapy releases air at a constant rate of pressure, rather than at two separate air pressure levels, and is generally reserved for use during sleep at home.

Doctors choose whether to first try BiPAP or CPAP therapy with a person based on the severity of their specific symptoms and underlying causes of the hypercapnia.

Supplemental Oxygen

Low oxygen levels often accompany high carbon dioxide levels, which is why controlled oxygen may be given to help treat acute hypercapnia.

Oxygen therapy may also play a role in less severe hypercapnia. When nighttime PAP therapy alone isn't able to treat a person's breathing issues, doctors may prescribe supplemental oxygen to be used in conjunction with PAP therapy. A person may only need to use both PAP therapy and supplemental oxygen for a certain period of time, then, after the hypercapnia improves, they may be able to use PAP therapy alone during sleep.

Medication

In certain cases of hypercapnia, medications may be prescribed to help with treatment. The types of medication prescribed depend on the severity of the hypercapnia and its underlying causes. For example, when a person has COPD, a bronchodilator and corticosteroid may be inhaled through a nebulizer. Antibiotics are prescribed when there's a lung infection, and medications that help remove excess fluids might be needed if there are signs of heart failure.

Invasive Mechanical Ventilation

In the case of hypercapnia, invasive mechanical ventilation is a treatment often reserved for people who have lost consciousness, or those who do not improve with other treatments, like PAP therapy. Invasive mechanical ventilation stabilizes breathing through intubation. With intubation, air is delivered through a temporary, nonsurgical tube that enters directly into a person's windpipe.

When to Talk to Your Doctor

Talk with your doctor if you believe you may have symptoms of hypercapnia. If you’re experiencing difficulty breathing, headaches, sluggishness, or other symptoms of severe hypercapnia, seek medical attention immediately. These may be signs of a more serious respiratory or medical condition.

Hypercapnia is often a sign of a larger health issue, which is why it’s important to seek diagnosis and treatment right away if you notice possible symptoms.

Frequently Asked Questions

What is permissive hypercapnia?

Permissive hypercapnia describes high blood carbon dioxide levels that doctors intentionally allow to happen while a person is on mechanical ventilation. Because doctors are allowing it to happen and monitoring it, permissive hypercapnia is generally safe and doesn't require treatment.

Permissive hypercapnia isn't something that doctors try to bring about. Instead, it's something that’s allowed to continue when it happens during the necessary treatment of a disorder, like acute respiratory distress syndrome, severe asthma, or chronic obstructive pulmonary disease. Permissive hypercapnia isn't always safe in pregnant people or people with certain brain and heart disorders.

Can asthma cause hypercapnia?

In some cases, the exacerbation of asthma may cause hypercapnia. This is because asthma can cause "air trapping," or air that remains in the lungs even after a person breathes out, which can lead to not enough carbon dioxide being released.

Can hypercapnia be reversed?

Whether or not hypercapnia can be reversed depends on its cause. Hypercapnia can usually be reversed when the underlying cause can be effectively treated or managed. For example, treating sleep apnea with PAP therapy may improve or reverse hypercapnia. Similarly, when hypercapnia is caused by sedative use or overdose, it’s generally reversible and treatment is only required as the sedative wears off.

Can hypercapnia cause brain damage?

Mild hypercapnia isn’t likely to cause brain damage, and permissive hypercapnia may even have protective effects. But, when hypercapnia is severe, it can increase the risk of seizures and stroke, which can both cause brain damage. Severe hypercapnia can also be life-threatening and lead to death if not treated.