HYPERCAPNIA (Greek hyper-+ kapnos smoke) — the increased tension of carbon dioxide gas in an arterial blood and body tissues.
The normal tension of carbonic acid in an arterial blood at people designated by the term «normocapnia» is equal to 35 — 45 mm of mercury.
G.'s condition can be caused by the exogenous and endogenous reasons. Of an exogenous origin arises at inhalation of the air containing the increased quantity carbon dioxide gas (see). It can be connected with stay in the small isolated rooms, in mines, wells, in submarines, cabins of spaceships both autonomous diving and space space suits in case of failure of a revitalization system of the atmosphere, and also at some medical interventions, napr, in case of failure of the narcotic and respiratory equipment or at inhalation of Carbogenum. Can arise in the conditions of artificial circulation at insufficient removal of carbon dioxide gas, etc.
G. of an endogenous origin is observed at various patol, states which are followed by insufficiency of external respiration, disturbance gas exchange (see), it is also always combined with hypoxia (see).
Pathophysiological mechanisms and clinical manifestations
G.'s Influence on an organism depends on speed, duration and extent of strengthening of carbon dioxide gas in blood and fabrics. At increase of tension and content of carbonic acid in an organism there are shifts physical. - chemical structure of internal environment, a metabolism and disturbance of many fiziol, processes. Naturally leads to gas (respiratory) to acidosis (see) which considerably defines the general patofiziol, a picture G.; at the same time it is established that shifts, characteristic of G., in internal environment of an organism cannot be reduced entirely to effects of acidosis. The reduction of pH compatible to life, at G. can reach, according to different authors, size 7,0 — 6,5.
At G. there is a redistribution of ionic gradients on cellular membranes (e.g., an ion of Cl - moves to erythrocytes, an ion of K + from cells passes into plasma). Is followed by shift of curve dissociation of oxyhemoglobin to the right that indicates the reduction of affinity of hemoglobin to oxygen leading to decrease in oxygenation of an arterial blood, despite normal and even the increased partial pressure of oxygen in an alveolar air.
In initial stages of moderate G. (at the content of carbon dioxide gas in inhaled air within 3 — 6%) consumption by an organism of oxygen increases that is connected with the reactions of chemical thermoregulation directed to compensation of the thermal losses of an organism increased under the influence of carbonic acid. At long action even of small increase in content of carbon dioxide gas consumption by an organism of oxygen falls. At the expressed G. it goes down from the very beginning of its development that is caused by neuroendocrinal regulatory mechanisms and direct influence of the increased content of carbonic acid on metabolic processes. At G. the temperature drop of a body arising generally due to increase in a thermolysis is usually observed; however it is considered that considerable G. leads to frustration of all system of thermal control since carbonic acid oppresses a metabolism. Hypothermal effect of G. is, as a rule, easily reversible.
Exciting effect of carbon dioxide gas on a respiratory center is implemented through the specific receptors located in a reticular formation of a brainstem and also through the strengthening of ions of H+ perceived by carotid and other hemoretseptorny educations. At moderate G. the strengthened activity of a respiratory center can remain during a long term. At the accruing G. the promoting effect of carbonic acid stops and the initial phase of excitement of a respiratory center is replaced by its oppression, up to complete cessation of breath. Such change of phases can happen at various sizes of partial pressure of carbon dioxide gas (pCO 2 ): from 75 to 125 mm of mercury. and more (there correspond 10 — 25% of carbon dioxide gas in inhaled air with a standard atmospheric pressure). However in most cases the oppressing G.'s action begins to be shown when pCO 2 exceeds 90 — 100 mm of mercury. The oppressing action of high concentration of carbonic acid is connected with G.'s influence and the accompanying acidosis on the central nervous structures.
Of moderate degree (pCO 2 50 — 60 mm of mercury.) it is quite often observed at patients with hron, respiratory insufficiency, and also during anesthesia (at preservation of spontaneous breath) using the anesthetics oppressing a respiratory center and reducing the volume of ventilation (Ftorotanum, cyclopropane, metoksifluran). Such G. at the awake person leads to decrease in working capacity, and during anesthesia can cause complications (strengthening patol, reflexes, a long postanesthetic depression) though after the termination of an anesthesia tension of carbon dioxide gas is normalized independently.
Exerts considerable impact on cardiovascular system. At moderate G. changes are connected with strengthening of a venous inflow to heart, increase in systolic volume as a result of increase in a tone of veins and skeletal muscles, redistribution of a blood-groove; considerably the brain and coronary blood stream increases, blood supply of kidneys and a liver can increase; a little blood supply of skeletal muscles decreases. Sharply expressed G. leads to disturbances in the carrying-out system of heart, to falling of a tone of peripheral vessels and the arterial hypotension passing into a collapse. Mechanisms of changes of a hemodynamics at G. are defined by the central and local effects of the increased concentration of carbon dioxide gas, hydrogen ions, and in some cases and the accompanying hypoxia.
Has preferential depressive effect on a nervous system of G.: excitability of the spinal centers goes down, carrying out excitement on nerve fibrils is slowed down, the threshold of convulsive reactions, etc. raises. Excitement of some departments of c. N of page, observed at moderate G., it is connected with the strengthened afferentation from the peripheral receptor educations irritated physical. - chemical shifts of internal environment; on EEG at the same time the desynchronization test is noted. It is impossible to exclude, however, and a possibility of short-term increase in excitability of neurons as a result of the direct depolarizing action of. At high concentration of carbonic acid (over 10%) there is a motive excitement with spasms, and then this state is replaced all by the increasing oppression — so-called narcotic effect of carbon dioxide gas, the mechanism to-rogo is found insufficiently out.
The question of the extreme concentration of carbon dioxide gas in air allowing long stay without prejudice to health and without decrease in working capacity and also a question of a possibility of adaptation by is not quite clear. Experiments showed that at long breath by air with impurity of 1 — 3% of carbon dioxide gas the acidosis arising in the beginning in several days is compensated for the account of a delay of bicarbonates, strengthenings of an erythrogenesis and other adaptive mechanisms. However at the animals who were in the atmosphere with impurity of 1,5 — 3% of carbon dioxide gas within 20 — 100 days changes in bodies are noted a growth inhibition and gistol. According to a number of authors, efficiency of the person can remain, changing, but not being lost, at the content in inhaled air of 1% of carbon dioxide gas within a month and more, at 2 — 3% — within several days, at 4 — 5% — within several hours; 6% of carbon dioxide gas are a limit when the condition of the person sharply worsens and working capacity is broken. At concentration of carbon dioxide gas to 10% the condition of the person is broken in 5 — 10 minutes, and at 15% — opacification of consciousness occurs in 2 min. Human life and the highest animals at concentration of carbon dioxide gas in 15 — 20% can remain within many hours and even a row of days. Deadly concentration — 30 — 35%; death comes not at once, and in several hours.
Inhalation of Carbogenum finds application in medicine at poisonings with carbon monoxide or drugs, in the postoperative period and in other situations, when there is no serious disorders of function of a respiratory center, but it is required to increase the volume of ventilation due to deepening of breath (presence at the inhaled mix 5 — 7% of carbon dioxide gas stimulates a respiratory center). Questions of positive influence of G. on processes of a saturation and desaturation of nitrogen are investigated during the diving and lacunar works, about a possibility of use of G. for receiving a deep hypothermia in the conditions of artificial circulation (see the Hypothermia artificial), etc.
Accurate dependence between the pCO level 2 and a wedge, manifestations G. are absent; does not cause a specific pathoanatomical picture G.
Clinical manifestations are changeable and deprived of specific diagnostic characters. At chronic G. with moderate increase in pCO 2 the wedge, signs are observed seldom in connection with gradual adaptation of systems of an organism. A wedge, manifestations are inherent to hl. obr. sharply developing. At the same time the shifts (respiratory acidosis) caused by G. do not depend on in what way — endogenous or exogenous — there was an increase in content of carbonic acid in an organism.
At acute poisoning with carbon dioxide gas appear an asthma at rest, nausea and vomiting, a headache, dizziness, cyanosis of mucous membranes and face skin, strong sweating, is broken sight. The most important sign of G. — the depression amplifying in process of increase of tension of carbonic acid in an organism. At increase in pCO 2 approximately to 80 mm of mercury. ability to concentrate attention is broken, the somnolence, confusion of consciousness appear; at increase in pCO 2 to 90 — 120 mm of mercury. the victim faints, it has patol, reflexes; pupils are usually evenly narrowed.
At hron. — changes of psychomotor activity (the excitement which is replaced by a depression), the headache and nausea are expressed less; the strong fatigue and persistent hypotension are generally observed.
Breath goes deep with a tendency to increase of respiratory excursions in the beginning that leads to increase in minute volume of ventilation; however at hron, respiratory insufficiency reaction of an organism to carbon dioxide gas as on a stimulator of ventilation is significantly weakened (same it is noted at use of anesthetics, drugs, relaxants). At G.'s increase respiratory cycles urezhatsya gradually, appears patol, breath, can occur dead stop of breath.
As a result of a vazodilatation bright pink coloring of skin appears. Pulse of usually good filling, rare, but maybe is speeded up, the ABP considerably raises (increase in cordial emission). But with increase in tension of carbonic acid cordial emission decreases, the ABP decreases. However changes of pulse rate and size ABP are changeable and cannot be reliable signs. Quite often is followed by arrhythmias, more often separate or group extrasystoles that usually does not constitute danger, but in the conditions of anesthesia Ftorotanum or cyclopropane of arrhythmia can gain the menacing character (fibrillation of ventricles of heart).
Small degree of G. influences a little or slightly raises a renal blood stream and glomerular filtering (release of urine increases a little); at high pCO 2 in connection with reduction of the bringing arterioles in balls the amount of the urine emitted by kidneys decreases (see. Oliguria ).
Coma can be one of terrible complications of G., development to-rogo is observed upon transition from breath by giperkapnichesky mixes on breath by oxygen; at transfer of breath into air the deep hypoxia able can develop to be a cause of death.
G.'s Condition can be established according to indications of devices, and also to assume on subjective signs and objective indicators. However only reliable criterion as acute, and hron. Definition of pCO serves 2 in an arterial blood. Research of indicators acid-base equilibrium (see) finds dekompensirovanny respiratory acidosis (see) which in the subsequent is compensated for the account of emergence metabolic alkalosis (see).
Tool diagnosis of G. is based on direct or indirect measurement of tension of carbon dioxide gas in an arterial blood.
Direct measurement is performed in test of the arterial or arterialized blood taken from a finger, an electrochemical method on change of EMF of electrode system at contact of the last with the analyzed environment. The electrode system represents a glass electrode for measurement pH and an auxiliary chlorsilver electrode shipped in the buffered solution containing Na bicarbonate or To. Both electrodes are connected by an electric chain to the high-resistance amplifier. Electrolyte and a pH-electrode are separated from a blood sample by a membrane, permeable for carbon dioxide gas, but liquid-tight. At contact with a gas-permeable membrane the carbon dioxide gas dissolved in blood diffuses through a membrane in bicarbonate solution of an electrode, changing at this its pH that in turn leads to change of size EMF in an electric chain. Such electrode system for direct measurement of pCO 2 blood is the main node of a number of foreign models of gas analyzers. The gas analyzer of AZIV-2 released by the domestic industry provides indirect definition of pCO 2 according to O'Sigor-Andersen's nomogram on the basis of definition of pH of blood. In certain cases G. can be indirectly established by measurement and record of concentration of carbon dioxide gas in an alveolar air — a kapnografiya by means of an optico-acoustic gas analyzer, action to-rogo is based on measurement of degree of selective absorption of infrared radiation by carbon dioxide gas. The domestic industry the gas analyzer of carbon dioxide gas the low-inertia GUM-3 allowing to make express diagnosis is issued (see. Gas analyzers , Gasometry ).
At acute G.'s signs of an exogenous origin first of all it is necessary to bring the victim out of the atmosphere with the increased content of carbon dioxide gas (to eliminate failure of the narcotic device, to replace the inactivated absorbent of carbon dioxide gas, at disturbance of a revitalization system — urgently to recover normal gas composition of inhaled air). The only reliable way of removal of the victim from coma — the emergency use of artificial ventilation of the lungs (see. Artificial respiration , artificial ventilation of the lungs). Oxygen therapy (see) it is unconditionally shown only at G. of an exogenous origin and in combination with artificial ventilation of the lungs. At G. inhalation of oxygen-nitrogen gas mixture renders good therapeutic effect (oxygen to 40%); this effect is noted in experiences with a barometric pressure of 760 mm of mercury.
Endogenous G. is liquidated at treatment of acute respiratory insufficiency. It must be kept in mind that at disturbance of the central regulation of breath (at most of patients with an aggravation hron, respiratory insufficiency, at poisoning with drugs, barbiturates, etc.) uncontrolled use of oxygen can lead to a bigger oppression of ventilation and G.'s increase since the effect of a hypoxia on a respiratory center is eliminated.
Easy G. (to 50 mm of mercury.) does not render on life activity of an organism of significant effect even at long influence: of 1 — 2 month — on the persons working in bottletight rooms about many years — on the patients suffering hron, respiratory insufficiency. Portability and G.'s outcome at higher pCO 2 is defined by fitness, composition of the inhaled gas mixture (air or oxygen) or existence of a disease of cardiovascular system.
At breath by air increase in pCO 2 to 70 — 90 mm of mercury. causes the expressed hypoxia, edges at further progressing of G. can serve as a cause of death. Against the background of breath by oxygen achievement of pCO 2 90 — 120 mm of mercury. causes the coma demanding emergency to lay down. died.
The exact term after which it is still possible to bring the person out of coma is unknown; this term of subjects is shorter, than the general condition of the patient is heavier. However timely emergency treatment it is possible to warn death even if the person is in coma within several hours and even days.
Cases of a happy end of G. which arose during anesthesia with increase in pCO are known 2 to 160 — 200 mm of mercury.
Prevention provides absorption of carbon dioxide gas during the work in bottletight rooms, observance of rules of work with devices for an anesthesia and artificial ventilation of the lungs and the principles of carrying out the general anesthesia, timely treatment of the diseases which are followed acute or hron, respiratory insufficiency. Specific methods of increase in resistance of an organism to action of the increased concentration of carbon dioxide gas are not developed yet.
Features of a hypercapnia in the conditions of aviation and space flight
At the pilot G. it is improbable since the small volume of harmful space of oxygen masks, moderate physical. activity of crew in flight, relative short duration of flight exclude accumulation of carbon dioxide gas in inhaled air. At failure of systems of ventilation the pilot can use emergency system of oxygen food and stop flight.
Big potential danger of emergence of G. exists in space flight owing to a possibility of accumulation of carbon dioxide gas in the atmosphere of a cabin or in a pressure helmet of a space suit at failure oxygen and respiratory equipment (see). However some excess of carbon dioxide gas in a cabin can be allowed by the program of flight from reasons of economy of weight, dimensions and power supply of a life support system, and also for the purpose of strengthening of regeneration of oxygen and prevention hypocapnies (see), etc. But programs of modern flights of any strengthening of carbon dioxide gas over applied fiziol, limits are not allowed (1% — for days of flights and 2 — 3% — for hours of flight).
If increase of concentration of carbonic acid to toxic level happens within several minutes (or hours), at the person the state acute develops. Long stay in the atmosphere with moderately raised gas content brings to hron. G. Calculations show that at failure of rantsevy system of absorption of carbon dioxide gas in a space space suit in operating time of the astronaut on the surface of the Moon the toxic level of carbon dioxide gas in a pressure helmet will be reached in 1 — 2 min.
In a cabin of the spaceship like Apollo it can happen to three astronauts performing work, usual for them, more than for 7 hours after system crash of regeneration. In both cases emergence acute is possible. At smaller malfunctions in work of system of absorption of carbon dioxide gas in long flights premises for development hron are created.
G. in space flight is fraught with heavy complications and in connection with the «return» effect of carbonic acid (a wedge, its symptoms are opposite to direct action) since after transfer of breath into normal gas mixture of disturbance in an organism often not only do not weaken, but even amplify.
Content of carbon dioxide gas is within 0,8 — 1% (6 — 7,5 mm of mercury.) it is possible to consider tolerance level for short-term and long stay both in a cabin, and in a pressure helmet. If the astronaut has to work within several hours in a space suit, then the content of carbon dioxide gas in a pressure helmet shall not exceed 2% (15 mm of mercury.); though at the astronaut working capacity (short wind and exhaustion develop) decreases a little, work can be performed in full.
At the content of carbon dioxide gas in inhaled air to 3% (22,5 mm of mercury.) the astronaut can perform easy work within several hours, however at the same time the expressed short wind, a headache and other symptoms is observed; therefore increase in content of carbon dioxide gas in a pressure helmet of a space suit or in a cabin to 3% also needs to be considered as the situation which is subject to immediate elimination.
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H. I. Losev; V. A. Gologorsky (general rubbed.), And. H. Chernyakov (av. medical), V. M. Yurevich (instr. diagn.).