An Overview of Respiratory Acidosis

Recognize the symptoms of this dangerous condition

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Respiratory acidosis (primary hypercapnia) is when blood becomes too acidic because your lungs are unable to remove enough carbon dioxide from your body. This potentially life-threatening condition can be caused by sudden illness, a drug overdose, or a long-term disease that affect the lungs.

Acidic blood can lead to increasingly serious symptoms, starting with sleepiness and progressing to coma. Respiratory acidosis is a medical emergency that requires prompt diagnosis and treatment.

This article looks at the symptoms and causes of respiratory acidosis plus how it’s diagnosed and treated.

Symptoms of Respiratory Acidosis

As carbon dioxide levels in your blood rise, blood flow to your brain increases. That leads to specific impairments, each of which is tied to certain symptoms.

Because respiratory acidosis puts the body under stress, it generally releases stress hormones (catecholamines). These may lead to further symptoms.

symptoms of respiratory acidosis.
 Madelyn Goodnight / Verywell

The most common symptoms of respiratory acidosis include:

  • Confusion
  • Anxiety
  • Being easily fatigued
  • Lethargy
  • Memory loss
  • Shortness of breath
  • Tremors (shaking or jerking muscle movements)
  • Warm and flushed skin
  • Sweating

Less common symptoms may be:

Some of these symptoms may occur early on. Others may develop later. For example, someone may at first be fatigued, become more lethargic, and eventually grow unresponsive and slip into a coma.

Cal 911

Severe respiratory acidosis is a medical emergency and requires immediate medical attention. If you suspect symptoms are developing, call 911 or get to an emergency room. If left untreated, it can lead to organ failure, shock, and even death.

Causes of Respiratory Acidosis

When your breathing becomes too impaired to clear carbon dioxide out of your blood, it’s called hypoventilation. Hypoventilation makes blood carbon dioxide levels rise, which makes your blood more acidic.

These changes may be acute (from sudden illness) or chronic (from long-term diseases).

In acute respiratory acidosis, carbon dioxide levels may build up very quickly due to an acute medical condition that disrupts the acid-base balance. These illnesses include:

  • Stroke
  • Drug overdose
  • Aspiration (such as choking on vomit)
  • Pneumonia

In acute disease, your kidneys may be able to keep your acid-base balance stable for a while. But as time goes by, they may not be able to keep compensating enough.

Chronic respiratory acidosis is the result of long-term illnesses including:

Shifting Acid-Base Balance

The pH scale is used to measure acidity or alkalinity. Higher numbers mean it’s more alkaline and lower numbers mean it’s more acidic.

The body’s acid-base balance is usually a pH level between 7.35 and 7.45. When it falls below 7.35, it’s called acidosis. If it goes above 7.45, it’s called alkalosis.

The balance can be shifted by:

  • Breathing out carbon dioxide (or an inability to)
  • Changes in metabolism that impact carbon dioxide or acid production
  • Bicarbonate excretion through the kidneys

Conditions that cause or contribute to respiratory acidosis include:

  • An impaired brainstem that doesn’t prompt normal breathing
  • Airway blockages diseases such as asthma and COPD
  • Inadequate movement of air (ventilation) or blood (perfusion) through the lungs

Brainstem Impairment

Your brainstem controls respiration (breathing). To do so, it sends signals to the respiratory muscles (especially the diaphragm) that make the lungs inflate (as you inhale) and deflate (when you exhale).

As the diaphragm contracts, it’s drawn down and allows the lungs to fill with air. As it relaxes, the lungs passively empty.

If the brainstem’s respiratory center is damaged, these signals aren’t sent and breathing is compromised. This kind of impairment can be caused by:

These abnormalities typically cause other symptoms, often affecting consciousness and contributing to unresponsiveness, in severe cases, coma.

Airway Blockage

Air can be blocked at various points before reaching your lungs. The windpipe (trachea) can be obstructed. Small grape-like sacs within the lungs—called alveoli—may become stiff or filled with mucus.

A blocked airway may gradually lead to respiratory failure and acidosis. Causal factors can include:

  • Aspiration (such as choking on vomit)
  • Asthma
  • COPD

These conditions may be associated with wheezing, shortness of breath, coughing, and other signs of breathing problems.

Inadequate Lung Tissue Ventilation and Perfusion

To rid the body of carbon dioxide, the blood must deliver it to functioning alveoli that are well ventilated (able to move air in and out properly). Compromised blood flow, or lung tissue that cannot be adequately filled with air, both affect function.

When there’s a mismatch between airflow (ventilation) and blood flow (perfusion), this leads to a condition called dead space ventilation. This loss of function can contribute to respiratory acidosis and may be due to:

Many of these problems lead to breathing difficulties that may become evident due to decreased oxygen levels.

Musculoskeletal Failure

The diaphragm is primarily responsible for expanding and filling your lungs. If this muscle fails, it can compromise your breathing.

Disorders that restrict lung expansion or weaken the muscles that aid breathing may gradually cause respiratory acidosis. Potential causes include:

Your healthcare provider may order tests to gauge the impact of these conditions on respiratory acidosis.

Diagnosis of Respiratory Acidosis

Respiratory acidosis typically gets noticed when someone shows signs of difficulty breathing or has a change in consciousness (being disoriented or passing out).

Sudden symptoms need emergency treatment. Gradual symptoms aren’t usually as urgent but you should call your healthcare provider or get checked out soon.

Your healthcare provider has many tools available to help them identify respiratory acidosis.

Physical Exam

During a physical examination, they’ll generally:

  • Listen to your heart and lungs
  • Assess blood circulation
  • Looking for airway blockages

If your provider determines your condition is unstable, they’ll move on to blood tests.

Initial Blood Tests

Blood tests for respiratory acidosis reveal the carbon dioxide and pH levels of your blood.

  • Arterial blood gas measurement: The most important diagnostic test. Measures oxygen and carbon dioxide levels in the blood.
  • Arterial CO2 tension (PaCO2): Measures carbon dioxide levels, partial pressure of oxygen, and the acidity of the blood.

In chronic respiratory acidosis, the PaC02 may be elevated with a normal or near-normal acidity level. This occurs when the kidneys compensate for acidosis.

Further Testing and Imaging

To identify the causes of respiratory acidosis, your healthcare provider may order:

More tests may be necessary depending on the suspected cause, especially if it may be due to an abnormality of the brain or musculoskeletal system.

Treatment of Respiratory Acidosis

If acute respiratory acidosis lasts for more than 12 hours, your kidneys will try to compensate by lowering your blood acidity. This process generally lasts for between three and five days.

However, it may not be enough to bring your acidity level back to normal, meaning you need treatment. The standard treatment is to improve your breathing and address the underlying cause of respiratory acidosis.

Noninvasive Positive-Pressure Ventilation

Your breathing may be improved with a continuous positive airway pressure (CPAP) or bilevel (BiPAP) machine. These devices are typically used to treat obstructive sleep apnea (OSA), but they can be used for acute cases of respiratory acidosis.

CPAP and BiPAP deliver pressurized air through a face mask over your nose and sometimes your mouth. That helps your lungs expel carbon dioxide.

This treatment is especially useful when pulmonary acidosis is caused by OSA, obesity hypoventilation syndrome, and neuromuscular failure. It may help you avoid intubation (having a breathing tube in your throat) and being put on a ventilator.

Oxygen Supplementation

If your blood oxygen level is low, you may be given additional oxygen.

However, oxygen therapy alone isn’t an effective treatment—it may actually suppress breathing in some cases, pushing the acidity even further.


If breathing difficulties progress, it may be necessary to put a breathing tube in your airway, where it can directly ventilate the lungs. This means you’ll need to be in an intensive care unit.

If you need this treatment, you’ll be sedated and restrained so you don’t accidentally rip out the tube. The tube is then connected to a ventilator, which helps your lungs breathe in oxygen and breathe out carbon dioxide.

Cause-Depended Treatments

Other treatments depend on the causes and contributing factors of your respiratory acidosis. These may include:

  • Medications: Bronchodilators and corticosteroids may reverse some types of airway obstruction, such as those from asthma or COPD.
  • Smoking cessation: Smokers will be encouraged to quit. Smoking contributes to airway dysfunction, and avoiding additional damage may prevent future problems.
  • Weight loss: In obesity hypoventilation syndrome, significant weight loss may reduce abnormal lung compression. If diet and exercise aren’t enough, weight loss surgery may be suggested.
  • Avoiding sedatives: Stay away from opioid pain medication and benzodiazepines (anxiety drugs). If you must take one (with your healthcare provider’s approval), never combine them with alcohol.
  • Sleep apnea treatment: If OSA is a causal factor, treating it with CPAP or BiPAP can help prevent respiratory acidosis. You may be sent for a sleep study to diagnose OSA.


Respiratory acidosis is a potentially life-threatening condition in which your blood becomes too acidic. This is usually due to a breathing problem.

Breathing problems may be caused by problems with brain signals that control breathing, a blocked airway (aspiration, asthma), impaired lung function (pneumonia, pulmonary fibrosis), and musculoskeletal problems (diaphragm dysfunction, diseases of the nerves or muscles).

Diagnosis involves a physical exam, blood tests for carbon dioxide and acid levels, lung function tests, and imaging.

Treatment involves breathing assistance and resolving or managing the underlying cause(s).

A Word From Verywell

If you think you have respiratory acidosis, don’t hesitate—call 911 or get to an emergency room right away.

Once you get a proper diagnosis and treatment, you can get better and hopefully prevent future recurrences. Be sure you follow your healthcare provider’s directions for treating both respiratory acidosis and any conditions that may have caused it.

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By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.