What is Hypercapnia?

Causes, Symptoms, and Treatment of Carbon Dioxide Retention in the Blood

Alveoli in the lungs.
Alveoli in the lungs. Dorling Kindersley/Getty Images

Hypercapnia is a condition that occurs when there is too much carbon dioxide—a waste product of respiration—in the blood. While it is sometimes caused by things such as hypoventilation or a narcotic drug overdose, a common cause is the lung disease, COPD.

The COPD and Hypercapnia Link

Generally speaking, when we breathe, we inhale oxygen and exhale carbon dioxide. These two respiratory gases are exchanged deep within the lungs, in tiny, grape-like clusters, or air sacs, called alveoli.

In people with COPD, this process is impaired because the alveoli are destroyed, leaving less surface area for oxygen to get from the lungs into the bloodstream and for carbon dioxide to get from the blood into the lungs to be exhaled. This results in a low amount of oxygen in the blood, a condition called hypoxemia, and high levels of carbon dioxide in the blood, a condition called hypercapnia. 

This retention of carbon dioxide in people with COPD is due to a process called ventilation-perfusion mismatch (V/Q mismatch) in the lungs. This occurs when, simplistically, the capillaries and alveoli in the lungs don't line up as well as usual for the proper exchange of gases to take place. 

Causes of Hypercapnia

Aside from COPD, there are other conditions that can lead to high levels of carbon dioxide in the blood. Some examples include:

  • Hypothermia
  • Certain metabolic disorders (for example, low phosphate and magnesium levels in the bloodstream)
  • Certain muscle or nervous system disorders like encephalitis, muscular dystrophy, ALS, or myasthenia gravis
  • End-stage Interstitial Lung Disease (ILD)
  • Obstructive sleep apnea
  • Obesity hypoventilation syndrome

    Symptoms of Hypercapnia

    Many people don't even realize they have hypercapnia. In cases where it develops slowly over time and is extremely mild, you may not experience any symptoms at all. If symptoms do occur, they may include a mild shortness of breath, headaches, inability to think straight, or feeling drowsy or sleepy. Because it's so easy to miss the signs of mile hypercapnia, awareness is key.

    On the other hand, symptoms of severe hypercapnia are more pronounced. Severe hypercapnia may eventually lead to respiratory failure and possibly death. Symptoms and signs may include:

    • Paranoia, depression, and confusion, which may progress to coma
    • Muscle twitches
    • Seizures
    • Dilation or widening of superficial veins in the skin
    • Papilledema—a sign of increased pressure in the brain

    Treatment for Hypercapnia

    Treatment for hypercapnia depends upon its severity, and starts with addressing the underlying cause. 

    • Noninvasive Ventilation: Noninvasive ventilation provides ventilatory support to a patient through the upper airways. It enhances the breathing process by giving the patient a mixture of air and oxygen from a flow generator through a tightly fitted facial or nasal mask.
    • Intubation and Mechanical Ventilation: Intubation is the process of inserting a special tube through the mouth and then into the airway. The tube then gets hooked up to a mechanical ventilator that takes over active breathing for the patient.

      When to Call the Doctor

      Hypercapnia can lead to respiratory failure and death if left untreated. If you have COPD, being aware of hypercapnia symptoms is key to early detection. Call your doctor as soon as possible if you experience any change in your symptoms or general health.

      Sources:

      Feller-Kopman DJ, Schwartzstein RM. (2017). The evaluation, diagnosis, and treatment of the adult patient with acute hypercapnic respiratory failure. In: UpToDate, Stoller JK (Ed), UpToDate, Waltham, MA. 

      Poon CS,  Tin C, Song G. Submissive hypercapnia: Why COPD patients are more prone to CO2 retention than heart failure patients. Respir Physiol Neurobiol. 2015. Sep 15;216:86-93.

      West JB. Causes of and compensations for hypoxemia and hypercapnia. Compr Physiol. 2011 Jul;1(3):1541-53.

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