Brief overview
- What is hypercapnia? Accumulation of carbon dioxide in the arterial blood. It can occur acutely or develop slowly.
- Causes: e.g. insufficient ventilation of the lungs (for example in COPD and other lung diseases), increased CO2 production in the body (for example in hyperthyroidism), metabolic alkalosis (for example as a result of potassium deficiency), inhalation of air rich in CO2
- Symptoms: e.g. sweating, accelerated breathing, accelerated heartbeat, headaches, confusion, unconsciousness
- Therapy: e.g. artificial respiration, administration of sodium bicarbonate, lowering of body temperature (hypothermia), treatment of the cause (e.g. the underlying disease)
Hypercapnia: causes and possible diseases
Hypercapnia is usually caused by insufficient ventilation of the lungs (hypoventilation), such as in the chronic lung disease COPD, in the context of which hypercapnia very often occurs.
Sometimes, however, carbon dioxide accumulation also develops as a result of increased carbon dioxide production, metabolic alkalosis or inhalation of air rich in carbon dioxide (carbon dioxide poisoning).
Hypercapnia due to hypoventilation
- Acute “lung weakness” (acute respiratory insufficiency)
- obstructive lung diseases (lung diseases 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 due to medication such as opiates (strong painkillers)
- Effect of muscle-relaxing medication (relaxants) lasting longer than desired after an operation
- Pickwick syndrome: a hypoventilation syndrome caused by obesity that is associated with hypercapnia. The lungs of those affected are insufficiently ventilated, particularly when lying down. Pickwick’s syndrome usually affects men over the age of 50.
Hypercapnia due to increased CO2 production
An accumulation of carbon dioxide in the arterial blood can also be caused by 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 an excessive amount of carbon dioxide, those affected can no longer breathe it out sufficiently. It accumulates in the blood – hypercapnia develops.
- “Blood poisoning” (sepsis)
- fever
- Polytrauma (simultaneous injury to different body regions or organ systems, whereby at least one injury or the combination of several injuries is life-threatening)
- Uncontrollable (malignant) high blood pressure
- hyperthyroidism (overactive thyroid gland)
Hypercapnia due to metabolic alkalosis
Hypercapnia can also occur as a reaction of the body to metabolic alkalosis. In this clinical picture, the bicarbonate level in the blood is greatly increased, causing the pH value to shift upwards, i.e. into the basic (alkaline) range.
The body then tries to lower the pH value back to normal by retaining more carbon dioxide and not exhaling it through the lungs – a compensatory hypercapnia develops.
Possible causes of metabolic alkalosis are, for example
- acute potassium deficiency
- Loss of a lot of acidic gastric juice (e.g. due to vomiting)
- Taking certain diuretic medications (diuretics)
- Overeating (hyperalimentation), i.e. an unhealthy diet that is too rich and leads to obesity
Hypercapnia due to inhalation of CO2-rich gas
The air in feed silos and brewery cellars, for example, can contain dangerous levels of carbon dioxide, which makes working there risky.
Carbon dioxide is an odorless gas, so those affected breathe it in unnoticed.
Hypercapnia: symptoms
Depending on its severity, hypercapnia triggers various symptoms. These are not specific to an accumulation of carbon dioxide in the blood and can therefore also have other causes.
Common symptoms of hypercapnia are
- sweating
- High blood pressure
- palpitations and cardiac arrhythmia
- Accelerated breathing (tachypnea)
- headaches
- confusion
- loss of consciousness
- tonic-clonic convulsions (convulsions with stiffening and twitching of arms and legs, e.g. during an epileptic seizure)
- dilated pupils (mydriasis)
A visit to the doctor is urgently recommended for such symptoms!
Clouding of consciousness (up to and including unconsciousness and coma) only occurs with more pronounced hypercapnia, i.e. with a partial pressure of carbon dioxide above 60 mmHg. At such values, the pressure in the brain increases because the blood vessels there dilate considerably.
Recently operated patients with hypercapnia often suffer from headaches, nausea and hallucinations.
Hyperacidity (acidosis)
If insufficient ventilation of the lungs (hypoventilation) is the reason for the hypercapnia and subsequently for the hyperacidity, doctors speak of 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 results and the patient’s symptoms are usually sufficient to make the diagnosis of “hypercapnia”. However, the diagnosis can be made more difficult if the patient is taking medication that masks the symptoms of hypercapnia. For example, cardiovascular drugs such as beta blockers can slow down the rapid heartbeat and high blood pressure medication can prevent the increase in blood pressure.
Once 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.
How the doctor treats hypercapnia
The doctor does not always have to treat mild hypercapnia. However, if the pH value drops significantly due to the accumulation of carbon dioxide, i.e. a pronounced hyperacidity (acidosis) develops, the doctor must intervene therapeutically. Various treatment measures are available.
Sodium bicarbonate must be administered very carefully, as the rising pH value may reduce the respiratory drive. This means that the patient breathes less, which causes the CO2 level in the blood to rise further.
If all other treatment options fail, the doctor can lower the patient’s core body temperature as a last resort in cases of hypercapnia. This so-called hypothermia slows down metabolic activity and thus reduces carbon dioxide production in the cells.
All these measures are used for symptomatic treatment – i.e. to combat the symptom of hypercapnia. However, the doctor must also treat its cause. For example, an appropriate therapy is initiated for the underlying disease (such as COPD).
