Hypercapnia

Martina Feichter studied biology with an elective subject pharmacy in Innsbruck and also immersed herself in the world of medicinal plants. From there it was not far to other medical topics that still captivate her to this day. She trained as a journalist at the Axel Springer Academy in Hamburg and has been working for since 2007 - first as an editor and since 2012 as a freelance writer.

More about the experts All content is checked by medical journalists.

Hypercapnia is an increased level of carbon dioxide (CO2) in the blood. This waste product of cell metabolism is normally exhaled through the lungs. Usually it is due to insufficient ventilation of the lungs (hypoventilation) when the gas accumulates in the blood. This can happen with the chronic lung disease COPD, for example. Read more about the possible causes and treatment of hypercapnia here.

Brief overview

• What is hypercapnia? Carbon dioxide build-up in the arterial blood. It can be acute or develop slowly.
• Causes: e.g. B. insufficient volume of the lungs (e.g. with COPD and other lung diseases), increased CO2 production in the body (e.g. with overactive thyroid), metabolic alkalosis (e.g. as a result of potassium deficiency), inhalation of CO2-rich air
• Symptoms: including sweating, accelerated breathing, accelerated heartbeat, headache, confusion, unconsciousness
• Therapy: e.g. B. artificial respiration, administration of sodium bicarbonate, lowering of the body temperature (hypothermia), treatment of the cause (e.g. the underlying disease)

Hypercapnia: causes and possible diseases

Hypercapnia is mostly due to insufficient ventilation of the lungs (hypoventilation), as is the case with the chronic lung disease COPD, in connection with which hypercapnia occurs very often.

Sometimes, however, carbon dioxide accumulation also develops as a result of increased carbon dioxide production, metabolic alkalosis or by breathing in air that is rich in carbon dioxide (carbon dioxide poisoning).

Hypercapnia due to hypoventilation

Very often hypercapnia occurs when the patient breathes too little or too shallowly (low tidal volume) - the lungs are therefore not adequately ventilated. Such hypoventilation can have different reasons, for example:

• acute "lung weakness" (acute respiratory insufficiency)
• obstructive pulmonary diseases (lung problems with narrowing or obstruction of the airways) such as COPD and asthma
• restrictive lung diseases (diseases in which the lungs can no longer develop and expand sufficiently) such as pulmonary fibrosis
• Pulmonary embolism
• ascending respiratory paralysis after spinal anesthesia (due to the anesthetic rising through the spinal canal)
• Respiratory depression from drugs such as opiates (strong pain relievers)
• Effect of muscle-relaxing drugs (relaxants) after an operation that goes beyond the desired period of time
• Pickwick syndrome: a hypoventilation syndrome caused by obesity (adiposity) and associated with hypercapnia. The lungs of those affected are inadequately ventilated, especially when they are lying down. Pickwick syndrome mostly affects men over 50 years of age.

Hypercapnia due to increased CO2 production

Carbon dioxide accumulation in the arterial blood can also result from increased CO2 production:

Carbon dioxide accumulates as a metabolic end product in the cells and reaches the lungs via the blood, where it is exhaled. However, if the cells produce excessive amounts of carbon dioxide, those affected can no longer breathe it out sufficiently. It accumulates in the blood - hypercapnia develops.

Possible causes of an increased metabolism and therefore an increased CO2 production are:

• "Blood poisoning" (sepsis)
• fever
• Multiple trauma (simultaneous injury to different body regions or organ systems, with at least one injury or a combination of several injuries being life-threatening)
• uncontrollable (malignant) high blood pressure
• Overactive thyroid gland (hyperthyroidism)

Hypercapnia due to metabolic alkalosis

Hypercapnia can also arise as a response of the body to metabolic alkalosis. In this clinical picture, the bicarbonate level in the blood is greatly increased, which shifts the pH value upwards, i.e. into the basic (alkaline) range.

The body then tries to lower the pH value back to normal by holding back more carbon dioxide and not exhaling through the lungs - a compensatory hypercapnia develops.

Possible causes of metabolic alkalosis are, for example:

• acute lack of potassium
• Loss of acidic gastric juice (such as vomiting)
• Taking certain water tablets (diuretics)
• Overeating (hyperalimentation), i.e. unhealthy and abundant nutrition that leads to obesity

Hypercapnia from inhaling CO2-rich gas

The carbon dioxide content of the air is usually around 0.04 percent. The first symptoms of hypercapnia appear from a proportion of four percent, and from a proportion of over 20 percent there is a risk of fatal carbon dioxide poisoning.

The air in feed silos and brewery cellars, for example, can contain a dangerous amount of carbon dioxide, which makes working there risky.

Carbon dioxide is an odorless gas, so those affected breathe it in without being noticed.

Hypercapnia: symptoms

Depending on the severity, hypercapnia triggers different symptoms. These are not specific for an accumulation of carbon dioxide in the blood, so they can also have other causes.

Common symptoms of hypercapnia are:

• sweat
• high blood pressure
• Palpitations and arrhythmias
• accelerated breathing (tachypnea)
• headache
• confusion
• unconsciousness
• tonic-clonic convulsions (convulsions with stiffness and twitching of arms and legs such as in an epileptic seizure)

• dilated pupils (mydriasis)

In the event of such symptoms, a visit to a doctor is urgently recommended!

The clouding of consciousness (up to unconsciousness and coma) only occurs with a more pronounced hypercapnia, i.e. with a carbon dioxide partial pressure above 60 mmHg. At such values, the pressure in the brain increases because the blood vessels there expand considerably.

Recently operated patients with hypercapnia often experience headaches, nausea and hallucinations.

Acidosis (acidosis)

The increase in carbon dioxide in the blood causes it to become acidic: the acidity (pH value) of the blood drops in the case of hypercapnia. If it falls below 7.2, organ damage can occur. A pH below 7.0 can be life threatening.

If a lack of ventilation of the lungs (hypoventilation) is the reason for the hypercapnia and subsequently for the acidosis, doctors speak of breath-related (respiratory) acidosis.

Hypercapnia: what does the doctor do?

If hypercapnia is suspected, the doctor measures the blood gases (oxygen, carbon dioxide) in the arterial blood and the oxygen saturation. The patient's results and symptoms are usually sufficient to make a diagnosis of “hypercapnia”. However, the diagnosis can be made more difficult if the patient takes medication that disguises the symptoms of hypercapnia. For example, cardiovascular drugs of the beta blocker type can slow down the rapid heartbeat and high blood pressure medication can prevent blood pressure from rising.

If the doctor has diagnosed hypercapnia, further examinations may be necessary depending on the cause of the hypercapnia, for example lung function tests for lung diseases.

This is how the doctor treats hypercapnia

The doctor does not have to treat mild hypercapnia in every case. However, if the pH value drops significantly due to the carbon dioxide enrichment, i.e. pronounced acidosis (acidosis) occurs, the doctor must intervene therapeutically. Various treatment measures are available.

For example, artificial respiration can improve the ventilation of the lungs and thus the exhalation of carbon dioxide. In other cases, the doctor gives sodium bicarbonate (sodium bicarbonate): Although it does not counteract hypercapnia (i.e. does not improve CO2 excretion), it can raise the pH value that has fallen.

The administration of sodium bicarbonate has to be done carefully, because the increasing pH value may reduce the breathing stimulus. This means that the patient breathes less, which further increases the CO2 level in the blood.

If all other treatment options fail, the doctor's last resort for hypercapnia can be to lower the patient's core body temperature. This so-called hypothermia slows down metabolic activity and thus reduces the production of carbon dioxide in the cells.

All of these measures are used for symptomatic treatment - that is, to combat the symptom of hypercapnia. In addition, the doctor must also treat the cause. For example, appropriate therapy is initiated for the underlying disease (such as COPD).

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