Hypercapnia is an increase in the carbon dioxide content in arterial blood of more than 45 mm Hg. The condition most often develops with a decrease in lung ventilation against the background of COPD and exacerbation of bronchial asthma. The cause of the syndrome is also neuromuscular pathologies, rib injuries, critical conditions. Hypercapnia is manifested by an increase in the frequency and rhythm of breathing, myocardial dysfunction, and various neurological symptoms. Blood gas analysis, chest x-ray, spirometry are used for diagnostics. Treatment includes adequate respiratory support and comprehensive drug therapy.
ICD 10
J96 R06.8
Meaning
Hypercapnia is not an independent nosological unit. It is a clinical syndrome in pulmonology, which reflects the inability of the respiratory system to maintain the physiological level of carbon dioxide in the blood. The term hypercapnia in the medical literature is identified with ventilation (“pumping”) respiratory failure. The true frequency of the syndrome has not been established, which is due to its high prevalence and frequent development against the background of other life-threatening conditions.
Causes hypercapnia
The appearance of hypercapnia is associated with a sharp drop or an inadequate increase in alveolar ventilation in cases where the resources of the respiratory system are not enough to maintain the function of external respiration. The most common causes of the syndrome are emphysema in severe COPD and status asthmaticus, which are accompanied by a sharp decrease in the volume of ventilation in the lungs. Other provoking factors of hypercapnia:
- Prolonged intubation. During ventilation, the volume of the dead space of the lungs increases to 50-70%, as a result of which carbon dioxide cannot be properly excreted from the body. The risk of hypercapnic respiratory failure increases if intubation was performed against the background of the development of PE.
- Neuromuscular diseases. With myasthenia gravis, polyneuropathy, amyotrophic lateral sclerosis, the respiratory muscles are affected and pulmonary ventilation deteriorates sharply. All patients with severe forms of such diseases suffer from hypercapnic insufficiency of respiratory function.
- Pathology of the central nervous system. The cause of hypercapnia are injuries, tumors and other pathological processes occurring with the defeat of the respiratory center. Without central regulation, the processes of external respiration become chaotic and ineffective.
- Injuries. Occasionally, hypercapnic syndrome develops with serious damage to the muscular and rib cage of the chest. Severe pain and mechanical obstruction limit the possibilities of straightening the lungs, increase the indicators of dead space.
- Critical conditions. Hypercapnia can occur with relative hypoventilation against the background of increasing stress on the respiratory system. This condition is observed in sepsis, various types of shock, thromboembolism.
Pathogenesis
Normally, about 0.03% of carbon dioxide is in the inhaled air, while up to 4% is in the exhaled air. This difference in concentrations is due to the processes of tissue respiration, as a result of which a large amount of CO2 enters the venous blood. Even more carbon dioxide (up to 5.5%) is in the alveolar environment, which includes an anatomical dead space that is not involved in gas exchange processes.
Carbon dioxide is removed from the body by a pressure gradient: the gas diffuses through the alveolar walls, is released into the environment on exhalation. The permeability of lung membranes for CO2 is up to 600 ml per minute at a pressure of 1 mmHg, which is 20-25 times greater than the oxygen diffusion capacity. Therefore, hypercapnia is less common than hypoxemia, mainly in severe respiratory disorders.
In case of violation of the ventilation function of the lungs and the development of hypercapnia in the blood, the pH decreases, respiratory acidosis occurs. The pathological condition causes narrowing of the vessels of the lungs while simultaneously dilating the arteries of other organs of the body, which worsens the diffusion of gases and aggravates the existing disorders. In acute hypercapnia, cerebral vasodilation occurs, intracranial pressure increases.
Hypercapnia symptoms
In the clinical picture, shortness of breath comes to the fore. The respiratory rate increases more than 30-35 times per minute, sometimes paradoxical breathing is observed – abdominal retraction and chest bulging on inspiration. Patients experience a constant lack of air, breathing becomes noisy and puffing. When trying to inhale deeply, it is necessary to strain the auxiliary muscles of the chest, abdomen and neck.
Due to the pathological effects of carbon dioxide, there are signs of disruption of the cardiovascular system. Systemic vasodilation is observed, due to which the skin acquires an intense pink color, becomes very warm to the touch. With hypercapnia, the heart rate increases and the strength of myocardial contractions increases. The defeat of the central nervous system is represented by sleep disorders, headaches, clapping tremor.
Complications
With a rapid increase in the amount of CO2 in the blood, cerebral edema develops, which results in a hypercapnic coma. At the same time, glycolysis and lactate formation are activated in the nervous tissue, which increases the phenomena of acidosis and aggravates the patient’s condition. The pH value of blood less than 7.2 is recognized as life-threatening. In case of chronic ventilation insufficiency, the work of the respiratory center and its adaptation to changes in oxygen indicators in the blood is disrupted.
Diagnostics
The examination of patients with acute form hypercapnia is carried out by resuscitators as part of emergency medical care. Chronic variants of respiratory disorders are in the competence of a pulmonologist. According to the indications, a cardiologist and a neurologist are involved in the consultation. To assess the severity of hypercapnia and identify the root cause of its development,:
- Chest X-ray. In acute hypercapnic insufficiency on the background of COPD or bronchial asthma, the picture of “clean” lungs is determined. Other causes of violations of the composition of blood gases can be visualized in the form of diffuse bilateral darkening, lobar or segmental lesions. On radiographs, it is also possible to determine rib injuries.
- Spirometry. The study of the functional ability of the lungs is necessary for patients with chronic hypercapnia to search for possible provoking factors. With emphysema, an irreversible decrease in FEV and FVC is observed, whereas partially reversible obstruction is typical for bronchial asthma.
- ECG. The study identifies signs of overload of the right heart, myocardial ischemia, hypertrophy of the left ventricle. In patients with long-term pulmonological pathology, a typical picture of a chronic pulmonary heart is diagnosed.
- CT brain. The study is carried out to exclude neurological causes of hypercapnia, if the development of pulmonary edema is suspected against the background of acute rapidly progressive respiratory failure. To clarify the diagnosis, an MRI of the brain is prescribed.
- Analysis of the gas composition of blood. According to the results of the study, an increase in the level of CO2 is determined while reducing the oxygen content. Additionally, the level of bicarbonates is investigated: an increase of more than 26 mmol/l indicates chronic hypercapnia, since it takes time to activate compensatory mechanisms.
Hypercapnia treatment
In acute hypercapnia, urgent therapeutic measures are prescribed, which are aimed at stabilizing respiratory function. Therapy is carried out in the ICU and begins with the restoration of adequate ventilation: checking the patency of the respiratory tract, prescribing non-invasive or invasive respiratory support with positive ventilation pressure. Pharmacotherapy of hypercapnia includes the following groups of drugs:
- Bronchodilators. Medications expand the lumen of the bronchi and facilitate lung ventilation, reduce the size of the dead space, so that excess CO2 is eliminated from the body faster.
- Mucolytics. Medications enhance the drainage function of the bronchi, promote the removal of viscous sputum from the respiratory tract, which can interfere with normal gas exchange.
- Diuretics. The drugs are used to complicate hypercapnia with cerebral edema and overload of the cardiovascular system. They are prescribed under constant monitoring of the water balance, sometimes in combination with intravenous infusion therapy.
After stabilization of the condition, patients undergo etiopathogenetic therapy aimed at eliminating the underlying disease that caused hypercapnia. In addition to medications, postural drainage techniques, physical therapy, and physiotherapy are used in complex treatment. In some neuromuscular diseases, prolonged ventilation is the only possible way to maintain the balance of blood gases.
Prognosis and prevention
The course of hypercapnia is determined by its root cause, the rate of development and the severity of symptoms. A more favorable prognosis is determined for patients with no organic lesions of the pulmonary parenchyma or respiratory muscles. Prevention consists in the prevention and early detection of chronic lung diseases, individual selection of parameters during ventilation.
Literature
- Thermoregulatory reactions of the human body to moderate hypercapnia. Mukhamedieva LN, Savina VP, Nikitin EI. Kosm Biol Aviakosm Med. 1989 Nov-Dec;23(6):51-4. link
- Body’s reaction to controlled hypercapnia during muscular exercise. Breslav IS, Shmeleva AM, Sidikov SM. Biull Eksp Biol Med. 1980 link
- A case of pulmonary embolism following acute respiratory failure with hypercapnia. Nakamura J, Matsushima T, Tomizawa S, Tanabe J. Nihon Kyobu Shikkan Gakkai Zasshi. 1991 link
- Hypercapnia: permissive and therapeutic. Kavanagh BP, Laffey JG. Minerva Anestesiol. 2006 link
- Obesity hypoventilation syndrome. Berger KI, Goldring RM, Rapoport DM. Semin Respir Crit Care Med. 2009 Jun;30(3):253-61. link