Respiratory acidosis is a decrease in the blood hydrogen index of less than 7.35, which is caused by excessive accumulation of carbon dioxide in the body. The condition develops against the background of bronchopulmonary pathology, neurological diseases, iatrogenic factors. It is manifested by respiratory insufficiency, depression of the higher functions of the central nervous system, cardiovascular complications. To diagnose acidosis, pH, gases and blood buffer systems are prescribed, capnography and ECG are performed. Treatment requires respiratory support by ventilator, improvement of the patency of the tracheobronchial tree, correction of the underlying pathology.
Respiratory acidosis is one of the most common conditions in the practice of a resuscitator, since it reflects non–specific disorders of the body. Pathology is mistakenly identified with hypercapnia, but this is not entirely correct: under certain conditions, a decrease in pH is possible with normal and even reduced carbon dioxide stress. Respiratory acidosis is not an independent diagnosis, so there is no data on its true prevalence.
Respiratory acidosis in most cases occurs against the background of ventilation respiratory failure, which is accompanied by changes in the composition of blood gases: an increase in the concentration of carbon dioxide and a decrease in oxygen levels. The following groups of diseases can be the cause of respiratory disorders:
- Chronic lung diseases. With bronchial asthma, COPD, obstruction of the bronchial tract, the respiratory volume and the effectiveness of lung ventilation sharply decrease, which contributes to the accumulation of carbon dioxide in the body.
- Depression of the respiratory center. Often there are neurological causes of respiratory acidosis, which are caused by damage to the medulla oblongata. Pathology develops against the background of injuries, neoplasms, toxic damage to the central nervous system.
- Weakness of the respiratory muscles. Insufficiency of respiratory function occurs with amyotrophic lateral sclerosis, myasthenia gravis and various myopathies. Weakness of the respiratory muscles is also observed in dermatomyositis, in people with severe obesity.
- Long-term ventilation. If the artificial ventilation mode is chosen incorrectly, it is not possible to achieve good gas exchange rates. In addition, with ventilation, the volume of dead space in the respiratory tract increases significantly, which exacerbates respiratory disorders.
Acidosis can occur during the normal operation of external respiration against the background of hypercatabolic disorders, which are accompanied by increased production of carbon dioxide in the body. This is observed with high fever and hyperthermic syndrome, thyrotoxic crisis, prolonged convulsive seizures. Hyperproduction of carbon dioxide occurs in patients with massive burns.
A high risk of respiratory acidosis is registered in diseases of the urinary system: glomerulonephritis, diabetic nephropathy, renal failure. Normally, the kidneys participate in the restoration of physiological buffer systems and secrete an excess of acidic compounds into the urine. With a decrease in the functional activity of the organ, the main way of compensation for pathologies of the acid-base state is lost.
For the proper course of all physiological processes, a stable acid-base equilibrium is required, which should be in the range of 7.35-7.45. Homeostasis is maintained due to the equilibrium between hydrogen protons H+ and the HCO3-bicarbonate buffer. Normally, the excess of positively charged particles is neutralized by bicarbonate, less important is the phosphate buffer, buffer systems of hemoglobin and other proteins.
Since hydrogen protons are formed from it when carbon dioxide CO2 enters the lungs, blood acidification is observed in hypercapnia and respiratory acidosis develops. Against the background of violations of the bronchopulmonary system or the respiratory center, such a condition cannot be compensated by an increase in the minute volume of ventilation, therefore acid-base disorders increase.
In the absence of intensive therapy in the first hours of the development of respiratory acidosis, there are violations of tissue respiration, anaerobic glycolysis is activated and an excess of lactic acid is formed. As a result of metabolic disorders, the pH level decreases even more. This condition is called mixed acidosis, has a severe course and is difficult to medically correct.
The clinical picture depends on the rate of pH decrease and the increase in the concentration of carbon dioxide. In an acute condition, the compensatory systems of the body do not have time to adapt, typical manifestations of respiratory failure develop. Chronic forms of respiratory acidosis activate adaptive mechanisms, so the pathology is asymptomatic, it is detected only during examination for another reason.
Acute acidosis is characterized by respiratory syndromes: shortness of breath, participation of auxiliary muscles in the act of breathing, noisy and puffing breathing. Patients complain of a feeling of lack of air, try to inhale deeply, straining the muscles of the press and resting on their hands. Severe forms of the disease are manifested by increasing anxiety, which is gradually replaced by drowsiness and stupor.
With respiratory acidosis with hypercapnia, there is redness of the skin due to the expansion of peripheral vessels, increased sweating, palpitations. Complaints of headaches are associated with an increase in intracranial pressure, increased cerebral blood flow. With critical violations of the water-electrolyte balance, muscle cramps, tremors, epileptiform seizures occur.
In conditions of acute respiratory acidosis, a decrease in the pH in the cerebrospinal fluid occurs much faster than in the blood, which is fraught with a deep depression of the central nervous system. The condition is manifested by disorientation, focal neurological symptoms. Cerebrospinal hypertension and arterial hypoxemia occur quickly, which become triggering factors for the development of coma.
The defeat of the cardiovascular system is fraught with bradycardia up to cardiac arrest, life-threatening arrhythmias. With hypercapnia, there is a spasm of the arterioles of the renal glomeruli, which is manifested by oliguria and progressive renal insufficiency. In the absence of medical care, other organs are involved in the process, pulmonary hypertension, gastrointestinal disorders occur.
Examination of patients with acute manifestations of acidosis is carried out by a doctor of the intensive care unit as part of a comprehensive diagnostic and treatment program of emergency care. The detection of a chronic violation of the ABB of the blood is in the competence of the pulmonologist. The results of such research methods play an important role in making a diagnosis:
- Blood pH analysis. If a value below 7.35 is detected, acidosis is diagnosed, but the result does not make it possible to differentiate the metabolic and respiratory etiology of the process. To do this, a study of the gas composition of the blood is carried out, in which an increase in PaCO2 of more than 45 mm Hg is determined.
- Capnography. With constant monitoring of the composition of exhaled air, a decrease in the concentration of CO2 at the end of exhalation is determined against the background of an increase in PaCO2. The higher the difference between these two values, the greater the volume of alveolar dead space in the patient’s lungs.
- ECG. According to the study, depression of the T wave, ventricular extrasystoles, signs of a pulmonary heart are determined. With hypokalemia, atrioventricular blockages of 2-4 degrees are possible. The results of the cardiogram are evaluated in combination with laboratory parameters.
- Blood test. With respiratory acidosis, an increase in the amount of topical bicarbonate occurs at the normal level of standard bicarbonate. The indicator of deficit/excess of buffer bases (BE) is moderately increased. Electrolyte disorders are represented by hypochloremia, hyperphosphatemia, hyperkalemia, which is gradually replaced by potassium deficiency.
In acute symptoms, hospitalization in the intensive care unit and non-specific measures to stabilize vital functions are indicated. Treatment of mild forms begins with improving the patency of the respiratory tract, for which infusion therapy is prescribed, rehabilitation of the tracheobronchial tree, humidification of the inhaled air mixture. Absolute indications for the transfer of a patient to a ventilator are:
- a decrease in the oxygenation index, which correlates with a decrease in the partial voltage of blood oxygen;
- an increase in hypercapnia of more than 55 mmHg;
- a drop in the pH level of less than 7.25;
- the presence of decompensated chronic diseases of the bronchopulmonary system.
After the elimination of acute acidosis, etiopathogenetic therapy is prescribed, taking into account the root cause of the ABB disorders that have arisen. The patient undergoes therapy under the supervision of a pulmonologist, neurologist and other specialists. It is possible to prescribe bronchodilators and mucolytics, postural drainage, physiotherapy, respiratory gymnastics and physical therapy are also recommended.
Prognosis and prevention
The outcome for patients with respiratory acidosis depends on the degree of compensation of the condition, the causes of pathology, timeliness and adequacy of medical care. The prognosis is favorable with compensated violations of the ABB and the absence of life-threatening complications. For the prevention of acid-base balance disorders, early detection and lifelong therapy of chronic bronchopulmonary diseases, improvement of the method of selecting ventilator parameters are necessary.