Hypercapnia

While providing oxygen to the body, the respiratory system simultaneously removes a 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 abnormally elevated levels of carbon dioxide in the blood.

Epidemiology

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

Among patients with severe hypercapnia, the fatal outcome due to respiratory failure averages 65%.

Causes of the hypercapnia

Doctors-pulmonologists name such causes of increased carbon dioxide (its partial pressure - RASO2) in the blood as:

• chronic obstructive bronchitis and COPD;
• Asthma exacerbation and prolonged decrease in airway patency (obstruction) leading to asthmatic status;
• Pulmonary hypertension, which may be associated with damage to the alveoli in chronic obliterative bronchiolitis, pulmonary emphysema, pneumonitis, as well as silicosis and other pnemoconioses - occupational respiratory diseases;
• Adult respiratory distress syndrome;
• decreased respiratory volume, including pneumosclerosis (often caused by chronic bronchitis); lung atelectasis and chronic bronchiectatic disease; heart problems and some systemic diseases;
• nocturnal apnea, which negatively affects the balance of O2 and CO2 in the blood due to shallow and intermittent breathing; [1]
• decreased tone and/or elasticity of the diaphragm and intercostal respiratory muscles in myopathies of a dystrophic or neurologic nature, e.g., myasthenia gravis, amyotrophic lateral sclerosis, Guillain-Barré syndrome.

Hypercapnia and stroke, brain injury and brain neoplasms may be etiologically related - due to cerebral circulatory disturbance and damage to the respiratory center of the medulla oblongata.

In addition, there is also metabolic hypercapnia due to electrolyte imbalance (disturbance of acid-base state) in fever, hormonal disorders (hypercorticism, thyrotoxicosis), nephrologic diseases (renal failure), metabolic alkalosis, development of sepsis. [2]

Hypercapnia in children may be due to:

• congenital malformations of the bronchopulmonary system;
• neonatal respiratory distress syndrome;
• aspiration of neonatal airways with amniotic fluid and meconium;
• Persistent neonatal pulmonary hypertension.

In premature infants, lack of oxygen in the blood - hypoxemia and hypercapnia develop bronchopulmonary dysplasia, associated with prolonged artificial support of respiratory function (ventilatory support). [3]

Risk factors

In addition to frequent infectious lung lesions such as bronchopneumonia and pneumonia, and all chronic bronchopulmonary diseases, the risk of hypercapnia is increased in:

• smoking;
• high degree of obesity (if you are overweight with a BMI of more than 30-35, breathing 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, overdose of opium derivatives (depressing central respiration);
• thoracic deformities, particularly spinal curvature;
• autoimmune pathologies with systemic fibrosis (rheumatoid arthritis, cystic fibrosis, etc.);
• presence of genetic abnormalities - congenital central hypoventilation or curse of undine syndrome.

Pathogenesis

In the process of cell metabolism, carbon dioxide is produced in mitochondria, which then diffuses into the cytoplasm, intercellular space and capillaries - dissolving in the blood, i.e. By binding to hemoglobin of erythrocytes. And CO2 removal occurs during respiration by gas exchange in alveoli - diffusion of gas through alveolar-capillary membranes. [4]

In normal (at rest) respiratory volume is 500-600 ml; lung ventilation is 5-8 l/min, and alveolar minute volume is 4200-4500 ml.

Often equating hypercapnia, hypoxia, and respiratory acidosis, physiologists link the pathogenesis of increased partial pressure of carbon dioxide (RaCO2) in the blood to impaired ventilation - alveolar hypoventilation, which results in hypercapnia.

By the way, hypercapnia and acidosis are interrelated, because respiratory acidosis with a decrease in the pH of arterial blood, 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 seizures, and memory problems. [5]

But the decrease of CO2 level in blood - hypocapnia and hypercapnia (i.e. Its increase) - are diametrically opposite conditions. Hypocapnia occurs during hyperventilation of the lungs. [6]

But let us return to the mechanism of hypercapnia development. In the process of pulmonary ventilation, not all the exhaled air (about one third) is released from carbon dioxide, because some of it remains in the so-called physiological dead space of the respiratory system - the volume of air in its various segments, which is not immediately subjected to gas exchange. [7]

Bronchopulmonary diseases and other factors cause disorders of pulmonary capillary channel and structure of alveolar tissue, reduce the diffusion surface and reduce alveolar perfusion, and increase the volume of dead space, where O2 level is low and CO2 content is very high. And at the next respiratory cycle (inhalation-exhalation) carbon dioxide is not completely eliminated, but remains in the blood. [8]

For example, in chronic obstructive bronchitis, hypoxemia and hypercapnia are observed due to decreased alveolar ventilation, i.e., blood oxygen levels decrease and carbon dioxide levels increase. [9]

Chronic hypercapnia with low O2 content 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 impaired (most likely, genetically determined) function of central CO2 chemoreceptors in the medulla oblongata or chemoreceptors in the carotid bodies of the external wall of the carotid artery. [10]

Symptoms of the hypercapnia

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

Symptoms of hypercapnia may also be manifested by: drowsiness, hyperemia of the face and neck, tachypnea (rapid breathing), abnormal HR with arrhythmias, increased BP, convulsive muscle contractions and asterixis (oscillatory tremor of the hands), and fainting.

Dyspnea (shortness of breath) is quite common, although hypercapnia and shortness of breath may be related indirectly, as shallow but frequent breathing is seen in bronchopulmonary disease (leading to impaired alveolar ventilation).

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

An emergency condition is acute hypercapnia or acute hypoxemic lung failure.

And permissive hypercapnia refers to elevated partial pressure of CO2. Due to hypoventilation in patients on ventilator with lung injury in acute respiratory distress syndrome or exacerbation of bronchial asthma. [11]

Complications and consequences

Moderate to severe hypercapnia can cause notable complications and adverse effects.

Hypercapnia and hypoxia lead to oxygen deprivation of the body.

In addition, high carbon dioxide content in the blood causes an increase in cardiac output with a sharp rise in arterial and intracranial pressure; hypertrophy of the right ventricle of the heart (pulmonary heart); changes in the hormonal system, brain and CNS - with certain mental reactions and states of irritability anxiety and panic.

And, of course, sudden respiratory failure , which can lead to death, can occur. [12]

Diagnostics of the hypercapnia

Since impaired alveolar ventilation has many causes, examination of the patient, his/her anamnesis and complaints are complemented by investigations of respiratory organs, the state of respiratory muscles and cerebral circulation, detection of hormonal and metabolic disorders, renal pathologies, etc. Therefore, diagnosis may require the involvement of appropriate subspecialists.

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

Instrumental diagnostics is performed: lung spirometry, capnometry and capnography (determining 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. [13]

Treatment of the hypercapnia

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

First of all, these are bronchodilators: Alupent (Orciprenaline), Atrovent, Izadrin, Aerophylline, Hexaprenaline and others.

Physiotherapy is also widely used in obstructive bronchitis and COPD; for more information see. - Fphysiotherapy for chronic obstructive pulmonary disease.

Benzomopin, Azamolin, Oliphen and other antihypoxants are prescribed for oxygen deficiency. Thus, 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. [14], [15]

Ventilation for 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 delivered through a face mask) is used. [16]

Prevention

To avoid hypercapnia is essential:

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

Forecast

Hypercapnia has a variable prognosis that depends on its etiology. And it is all the better the younger the patient. [17]

And with severe hypercapnia, respiratory system dysfunction, cardiac arrest, and brain cell death from lack of oxygen are very real threats.