Hypercapnia

Providing the body with oxygen, the respiratory system simultaneously removes the product of metabolism - carbon dioxide (carbon dioxide, CO2), which the blood brings from the tissues to the alveoli of the lungs, and thanks to alveolar ventilation, it is removed from the blood. So, hypercapnia means an abnormally high level of carbon dioxide in the blood.[1]

Epidemiology

According to foreign statistics, with obesity with a BMI of 30-35, hypoventilation syndrome develops in 10% of cases, with a body mass index of 40 and above - in 30-50%.

Among patients with severe hypercapnia, death due to respiratory failure, on average, is 65%.

Causes of the hypercapnia

Pulmonologists call such reasons for an increase in the content of carbon dioxide (its partial pressure - PaCO2) in the blood as:

• chronic obstructive bronchitis and COPD ;
• exacerbation of asthma and prolonged decrease in patency (obstruction) of the airways, leading to  asthmatic status ;
• pulmonary hypertension , which may be associated with damage to the alveoli in  chronic bronchiolitis obliterans , emphysema, pneumonitis, as well as  silicosis  and other pneumoconiosis - occupational diseases of the respiratory tract;
• adult respiratory distress syndrome ;
• a decrease in respiratory volume, including with  pneumosclerosis  (often caused by chronic bronchitis); lung atelectasis  and chronic  bronchiectasis ; with heart problems and some systemic diseases;
• sleep apnea , which negatively affects the balance of O2 and CO2 in the blood due to shallow and intermittent breathing;[2]
• decrease in tone and / or elasticity of the diaphragm and intercostal respiratory muscles in myopathies of a dystrophic or neurological nature, for example, myasthenia gravis, amyotrophic lateral sclerosis, Guillain-Barré syndrome.

Hypercapnia and stroke, craniocerebral trauma and neoplasms of the brain can be etiologically related - due to cerebral circulatory disorders and damage to the respiratory center of the medulla oblongata.

In addition, metabolic hypercapnia is also noted, caused by an imbalance of electrolytes (disturbance of the acid-base state) with fever, hormonal disorders (hypercortisolism, thyrotoxicosis), nephrological diseases (renal failure),  metabolic alkalosis , and the development of sepsis.[3]

Hypercapnia in children may be due to:

• congenital malformations of the bronchopulmonary system ;
• syndrome of respiratory disorders in newborns ;
• aspiration of the respiratory tract of newborns with amniotic fluid and meconium;
• persistent pulmonary hypertension in newborns .

In premature infants, a lack of oxygen in the blood - hypoxemia and hypercapnia develop with  bronchopulmonary dysplasiaassociated with prolonged artificial respiratory support (ALV).[4]

Risk factors

In addition to frequent infectious lesions of the lungs - bronchopneumonia and pneumonia, as well as all chronic bronchopulmonary diseases, the risk of hypercapnia increases with:

• smoking;
• a high degree of obesity (if overweight with a BMI of more than 30-35, the breathing process is difficult);
• lung damage caused by inhalation of toxic substances , or inhalation of air containing abnormally high concentrations of CO2;
• hypothermia (hypothermia);
• lung cancer;
• large doses of alcohol, an overdose of opium derivatives (depressing central respiration);
• deformities of the chest, in particular, with curvature of the spine;
• autoimmune pathologies with systemic fibrosis (rheumatoid arthritis, cystic fibrosis, etc.);
• the presence of genetic anomalies - congenital central hypoventilation or  Ondine's curse syndrome .

Pathogenesis

In the process of cell metabolism, carbon dioxide is produced in their mitochondria, which then diffuses into the cytoplasm, intercellular space and capillaries - dissolving in the blood, that is, binding to the hemoglobin of erythrocytes. And the removal of CO2 occurs during respiration by gas exchange in the alveoli - the diffusion of gas through the alveolar-capillary membranes.[5]

Normally (at rest), the tidal volume is 500-600 ml; lung ventilation - 5-8 l / min, and the minute volume of alveolar ventilation - 4200-4500 ml.

Often equating hypercapnia, hypoxia and respiratory acidosis, physiologists associate the pathogenesis of an increase in the partial pressure of carbon dioxide (PaCO2) in the blood with  impaired ventilation  - alveolar hypoventilation, the result of which is hypercapnia.

By the way, hypercapnia and acidosis are interrelated, since  respiratory acidosis  with a decrease in arterial blood pH is a violation of the acid-base state with an increase in carbon dioxide in the blood, which is caused by hypoventilation. It is respiratory acidosis that explains headaches, daytime sleepiness, tremors and convulsions, memory problems.[6]

But a decrease in the level of CO2 in the blood - hypocapnia and hypercapnia (i.e., its increase) - are diametrically opposed states. In this case, hypocapnia occurs with hyperventilation of the lungs.[7]

But back to the mechanism of development of hypercapnia. In the process of pulmonary ventilation, not all exhaled air (about a third) is released from carbon dioxide, since part of it remains in the so-called physiological dead space of the respiratory system - the volume of air in its various segments, which does not immediately undergo gas exchange.[8]

Bronchopulmonary diseases and other factors cause disturbances in the pulmonary capillary bed and structure of the alveolar tissue, reduce the diffusion surface and reduce alveolar perfusion, and increase the volume of dead space, where O2 is low and CO2 is very high. And during the next respiratory cycle (inhalation-exhalation), carbon dioxide is not completely removed, but remains in the blood.[9]

For example, in chronic obstructive bronchitis, due to a decrease in alveolar ventilation, hypoxemia and hypercapnia are observed, that is, the level of oxygen in the blood decreases, and the content of carbon dioxide increases.[10]

Chronic hypercapnia with a low content of O2 in the blood may be in the absence of obvious causes, primarily from the respiratory system. And in such cases, alveolar hypoventilation is associated with a violation (most likely genetically determined) of the function of the central CO2 chemoreceptors in the medulla oblongata or chemoreceptors in the carotid bodies of the outer wall of the carotid artery.[11]

Symptoms of the hypercapnia

Slowly developing hypercapnia syndrome, more precisely, alveolar hypoventilation syndrome may be asymptomatic, and its first signs - headaches, dizziness, fatigue - are nonspecific.

Also, the symptoms of hypercapnia can manifest themselves: drowsiness, flushing of the skin of the face and neck, tachypnea (rapid breathing), heart rate disturbance with arrhythmia, increased blood pressure, convulsive muscle contractions and asterix (oscillatory tremor of the hands), fainting.

Quite often there is dyspnea (shortness of breath), although hypercapnia and shortness of breath may be indirectly related, since shallow, but frequent breathing is observed in bronchopulmonary diseases (leading to a deterioration in alveolar ventilation).

The clinical picture of severe hypercapnia is characterized by irregular heartbeat, convulsions, confusion and loss of consciousness, disorientation, panic attacks. At the same time - if the brain and heart do not receive enough oxygen - there is a high risk of coma or cardiac arrest.

The emergency is acute hypercapnia or  acute hypoxemic pulmonary insufficiency .

And permissive hypercapnia refers to elevated partial pressure of CO2. Due to hypoventilation in patients on mechanical ventilation with lung damage in acute respiratory distress syndrome or exacerbation of bronchial asthma.[12]

Complications and consequences

Moderate to severe hypercapnia can cause noticeable complications and negative consequences.

Hypercapnia and hypoxia lead to  oxygen starvation of the body .

In addition, high levels of carbon dioxide in the blood cause an increase in cardiac output with a sharp increase in arterial and intracranial pressure; hypertrophy of the right ventricle of the heart (cor pulmonale); changes in the hormonal system, brain and central nervous system - with certain mental reactions and states of irritability, anxiety and panic.

And, of course, respiratory failure can suddenly occur  , which can lead to death.[13]

Diagnostics of the hypercapnia

Since the violation of alveolar ventilation has many causes, the examination of the patient, his anamnesis and complaints complement  the study of the respiratory organs , the state of the respiratory muscles and cerebral circulation, the detection of hormonal and metabolic disorders, kidney pathologies, etc. Therefore, diagnostics may require the involvement of relevant highly specialized specialists.

Blood tests are needed for gas composition, pH, plasma bicarbonate, etc.

Instrumental diagnostics are carried out:  lung spirometry , capnometry and capnography (determining the partial pressure of arterial blood CO2),  X-ray examination of lung function , EEC; if necessary, ultrasound and CT of other systems and organs

Differential diagnosis is aimed at determining the etiology of hypercapnia.[14]

Treatment of the hypercapnia

When the cause of hypercapnia is precisely known, treatment is directed to the underlying bronchopulmonary disease and appropriate medications are prescribed.

First of all, these are bronchodilators: Alupent (Orciprenaline),  Atrovent , Izadrin,  Aerofillin ,  Hexaprenaline  , etc.

Also, with obstructive bronchitis and COPD, physiotherapy is widely used; for details, see - Physiotherapy for chronic obstructive pulmonary disease .

Benzomopine, Azamolin, Olifen and other  antihypoxants  are prescribed for oxygen deficiency. So, the drug Olifen (tablets and solution for injection) is contraindicated in patients with impaired cerebral circulation, and its side effects are limited to allergic urticaria and moderate arterial hypotension.[15], [16]

Mechanical ventilation with hypercapnia (with endotracheal intubation) is necessary in cases of  acute respiratory failure . And to improve gas exchange and prevent breathing problems and hypoxemia, non-invasive positive pressure ventilation (in which oxygen is supplied through a face mask) is used.[17]

Prevention

To avoid hypercapnia, you must:

• quit smoking and limit alcohol consumption;
• get rid of extra pounds;
• timely treat bronchopulmonary diseases, not leading to their transition to a chronic form, as well as control the condition in the presence of systemic and autoimmune pathologies;
• avoid inhalation of toxic gaseous substances
• maintain muscle tone (regular exercise and, if possible, sports activities).

Forecast

Hypercapnia has a variable prognosis, which depends on its etiology. And it's better the younger the patient.[18]

And with severe hypercapnia, dysfunction of the respiratory system, cessation of cardiac activity and death of brain cells from lack of oxygen is a very real threat.