ACID-BASE EQUILIBRIUM

From Big Medical Encyclopedia

ACID-BASE EQUILIBRIUM (synonym: acid-base equilibrium, acid-base balance, acid-base state) — the relative constancy of hydrogen ion exponent (pH) of internal environment of an organism caused by combined action of buffer and some physiological systems, defining full value of metabolic turning into cells of an organism. Change of an indicator To. - y. the river and a number of the related sizes (e.g., an alkaline reserve) confirms disturbances of gas exchange and metabolic processes in an organism and degree of their weight.

Life activity of an organism first of all is connected with processes of tissue respiration which ensuring requires receipt of enough oxygen and removal of excess of the carbon dioxide gas which is formed as a result of numerous reactions of interstitial exchange. Transport of oxygen and carbon dioxide gas is carried out by blood, edges represents one of the most important internal environments of an organism, To. - y. by river a cut it is studied most in detail. Along with to-tami (donors of protons — hydrogen ions) blood contains also the bases (acceptors of protons) which ratio of concentration defines active reaction of blood. Quantitatively active reaction of liquids of an organism is characterized or the concentration of hydrogen ions (protons) expressed in mol/l or hydrogen ion exponent — a negative decimal logarithm of this concentration — pH (power Hydrogen — «force of hydrogen»). The ratio between concentration to - t and the bases can change depending on intensity of these or those processes of a metabolism in an organism, however only a certain range of fluctuations of pH of blood — from 7,37 to 7,44 with the average size of 7,38 — 7,40 meets standard. The sizes pH are lower 6,8 and higher than 7,8 are incompatible with life. The size pH is equal in erythrocytes 7,19 ± 0,02. In spite of the fact that fluctuations of a normal amount of pH seem very small, actually they make apprx. 12% of their average concentration. More considerable changes of the size pH of blood towards increase or decrease are connected with patol, disturbances of exchange. Dependence of an organism on constancy of active reaction of internal environment testifies to his need for rather effective systems of maintenance of relative constancy of concentration of hydrogen ions for an organism, in particular relative constancy of pH of blood.

Such systems in a human body three is a complex buffer systems (see), capable to be acceptors r donors of hydrogen ions without essential shifts of the size pH of the environment; respiratory system (lungs) and secretory system (kidneys).

Buffer systems of an organism

the Most important buffer system of an organism is the bicarbonate buffer system of blood consisting from coal to - you (H 2 CO 3 ) and its salts — sodium bicarbonate (NaHCO 3 ) or potassium (KHCO 3 ), HCO having the general ion 3 - . The most part of these ions is released at dissociation of bicarbonates and suppresses dissociation weak and fragile to - you are H 2 CO 3 , edges in solutions easily breaks up to water and carbon dioxide gas. Therefore in water solutions coal to - you take place the following balance: CO 2 + H 2 <>O-H 2 CO <-> H + + HCO 3 - . The size pH in solution can be expressed through a dissociation constant of carbonic acid (pKH 2 CO 3 ) and ion concentration [HCO 3 - ] and molecules not dissociated [H 2 CO 3 ]. This formula is known as Genderson's equation — Gasselbalkh:

Square brackets designate equilibrium concentrations of ions and not dissociated molecule. Since true concentration of not dissociated molecules H 2 CO 3 in blood it is insignificant and is in direct dependence on concentration of the dissolved carbon dioxide gas — CO 2 , it is more convenient to use that option of the equation, in Krom of pKH 2 CO 3 it is replaced with the seeming dissociation constant of H 2 CO 2 , considering the general concentration of the dissolved CO 2 in blood. Then instead of concentration [H 2 CO 3 ] in the equation pCO can be substituted 2 — partial pressure of CO 2 in an alveolar air:

where L — a solubility coefficient of CO 2 in a blood plasma, and 6,10 — the size, a constant for blood of the person at 38 °. The mechanism of action of this buffer system is that at receipt in blood of rather large numbers to - t hydrogen ions — H + to - t connect to ions of bicarbonate — HCO 3 - , forming slabodissotsiiruyushchy coal to - they are H 2 CO 3 . If in blood the quantity of the bases increases, then they, interacting with weak coal to - that, form water and ions of bicarbonate. At the same time there are no noticeable shifts in the size pH. The mechanism and other buffer system of blood — phosphatic is same. A role to - you in this system is played monosubstituted phosphate — NaH 2 PO4, and a role of salt — disubstituted Na phosphate 2 HPO 4 . The general ion in this system is the ion of HPO 4 - . Buffer capacity of this system is less since also it is less phosphates in blood, than bicarbonates.

The most powerful buffer system of blood are proteins, especially hemoglobin (see). The dissociation constant of acid groups of hemoglobin changes depending on its oxygenation. At saturation of hemoglobin oxygen it becomes stronger to - that and increases receipt in blood of hydrogen ions; giving oxygen, hemoglobin becomes weaker to - that, its ability to connect hydrogen ions increases. In peripheral capillaries of a big circle of blood circulation hemoglobin of erythrocytes gives oxygen, and the product of fabric exchange — carbon dioxide gas comes to erythrocytes (CO 2 ). Under influence karboangidraza (see) carbon dioxide gas interacts with water, forming coal to - that (H 2 CO 3 ). Arising due to dissociation coal to - you surplus of hydrogen ions communicates the hemoglobin which gave oxygen, and HCO anions 3 - leave erythrocytes in plasma. In exchange for these anions ions of chlorine come to erythrocytes (Cl - ), for to-rogo a membrane of an erythrocyte of a pronitsayem, while an ion of sodium (Na + ), the second compound NaCl, remains in a liquid part of blood. Thanks to an exit of bicarbonate ions from erythrocytes the alkaline reserve of blood is recovered, thus the bicarbonate buffer system is closely connected with buffer system of erythrocytes.

The respiratory system

In capillaries of lungs comes unloading of buffer systems of blood from acid equivalents due to release of carbon dioxide gas. It is promoted substantially by transition of hemoglobin to oxyhemoglobin which thanks to the stronger acid properties forces out coal to - that from bicarbonates of blood. Carbon dioxide gas is emitted with expired air (see. Gas exchange ).

Though the respiratory system (lungs) considerably influences on To. - y. it is required to river, however a lung apprx. 1 — 3 min. to level shift To. - y. river in blood whereas buffer systems of blood for this purpose need only 30 sec. However value of the pulmonary mechanism consists that, emitting carbon dioxide gas to the environment, lungs quickly liquidate danger acidosis (see).

The renal diuresis

the Third mechanism participating in regulation of constancy of concentration of hydrogen ions in blood is a renal diuresis. Kidneys provide increase or decrease in concentration of bicarbonates in blood at corresponding changes of the size pH. Kidneys work more slowly, than lungs: to liquidate shift of pH in blood, it is necessary for them 10 — 20 hour. The main mechanism of maintenance of constant concentration of hydrogen ions from kidneys is the reabsorption of ions of sodium and secretion of hydrogen ions in renal tubules. In cells of renal tubules from coal to - you are formed bicarbonate therefore the alkaline reserve of blood increases. In a gleam of tubules, on the contrary, bicarbonates turn in coal to - that. In cells of tubules carbon dioxide gas under the influence of a karboangidraza connects to water, forming coal to - that, hydrogen ions a cut are allocated in a gleam of a tubule and connect to ions of bicarbonate there. At the same time the equivalent quantity of cations of Na+ comes to cells of renal tubules. H formed in a gleam of a tubule 2 CO 3 easily breaks up to CO 2 and H 2 O and in such look is brought out of an organism. This process promotes, except removal of excess of ions of H + , to saving of ions of sodium in an organism. Saving of sodium in an organism is promoted also by education in kidneys of ammonia as a result of oxidizing deamination of amino acids, to hl. obr. glutaminic (see. Deamination ). Ammonia instead of other cations is used in kidneys for neutralization and removal from an organism with urine to - t. A ratio between ion concentration of H + in urine and blood can make 800: 1, ability of kidneys to a conclusion of ions of H is so big + from an organism.

Speed of secretion of ions of H + , Na exchanged for ions + or NH 4 + , in a certain measure depends on concentration of carbonic acid in extracellular liquid, i.e. in tubules of kidneys mechanisms closely intertwine water salt metabolism (see) and To. - y. river. In essence, it is two parties of the same process: intensity of a delay is stimulated in an organism of ions of sodium with increase in pH of blood, and reduction of pH of blood limits process of a reabsorption of ions of sodium in the renal canalicular device.

Definition of indicators of acid-base equilibrium in clinic

To. - y. the river is one of the major indicators homeostasis (see). It is estimated on the basis of the size pH, the partial pressure (tension) of carbon dioxide gas (pCO 2 ), concentration of true (urgent) and standard bicarbonates of blood (SB), concentration of the buffer bases — BB (English buffer base), surplus of the bases in whole blood — BE (English bases excess).

The size pH of blood decides by an electrometric (electrometric) method on use of pH-meters (see. Hydrogen ion exponent ). The clinic defines two pH values of blood: pH true (urgent) represents an indicator of pH of whole blood or plasma, pH metabolic designates the size pH of blood or plasma after its correlation with the size pCO 2 . At healthy faces of size of true and metabolic pH are equal. At a metabolic acidosis the size pH of metabolic is lower than the size pH of true. At respiratory acidosis the indicator of pH metabolic is higher than an indicator of pH true. At a metabolic alkalosis the size pH of metabolic is higher than the size pH true, and at respiratory, on the contrary, below. Other indicator characterizing To. - y. the river, is the partial pressure of carbon dioxide gas (pCO 2 ), i.e. its pressure over blood, at Krom occurred dissolution of CO 2 in blood. The number of the dissolved CO 2 calculate on the equation of P = L*pCO 2 , where P — the number of the dissolved CO 2 in mm/l, L — a solubility coefficient for carbon dioxide gas (so-called coefficient of Bohr), pCO 2 — partial pressure of carbon dioxide gas in mm of mercury. Size L at a temperature of 38 ° is equal in blood to 0,0301 mm/l. Therefore at pCO 2 , equal 40 mm of mercury., P — 0,0301*40 = 1,2 mm/l. If the number of the dissolved CO 2 it is expressed in percents by volume, for transfer of this indicator in mm/l use a formula

1 mm/l of CO 2 it is equal 2,226 about. % of CO 2 . In blood carbonic acid exists in the form of CO 2 , H 2 CO 3 and bicarbonate ion of HCO 3 - . Relation

As the number of the dissolved CO 2 makes 1,2 mm/l, that quantity of H 2 CO 3 at assessment of a state To. - y. the river in a wedge, practice practically loses the value. Size pCO 2 at healthy faces at rest fluctuates within 35,8 — 46,6 mm of mercury., averaging 40 mm of mercury. At pathology pCO value 2 fluctuates within 10 — 130 mm of mercury. At ventilating insufficiency of pCO 2 quite often about 140 — 150 mm of mercury increase. Increase in pCO 2 it is observed at respiratory acidosises and a metabolic alkalosis whereas decrease it happens at a respiratory alkalosis and a metabolic acidosis (see. Alkalosis , Acidosis ). At respiratory acidosises increase in pCO value 2 serves as an indicator of insufficiency of alveolar ventilation. In this case increase in pCO 2 is an origin of respiratory acidosis. At a metabolic alkalosis increase in pCO 2 is a compensatory factor: carbonic acid, collecting in blood, neutralizes in it surplus of the nonvolatile bases.

At a respiratory alkalosis reduction of pCO 2 results from a hyperventilation, leads edges to excess removal of carbonic acid from an organism and development of a respiratory alkalosis. At a metabolic acidosis decrease in pCO 2 also results from a hyperventilation, but, unlike a respiratory alkalosis, excess removal of carbonic acid in this case is kompensatorno directed to reduction of acidosis.

In a wedge, assessment of pCO 2 it is necessary to define not only its size, but also to find out fiziol, sense of the available shifts, in particular, it is necessary to solve, shifts of this indicator are causal or compensatory. At a respiratory alkalosis increase in the size pH of blood is combined with decrease in pCO 2 , and at metabolic — with increase in pCO 2 . At respiratory acidosis reduction of the size pH is followed by increase in pCO 2 , and at a metabolic acidosis, on the contrary, its decrease.

The third indicator characterizing To. - y. the river, is amount of true (urgent) and standard bicarbonates of blood. Any change of pCO 2 considerably affects absorption of carbon dioxide gas blood. Dependence of maintenance of CO 2 in blood from pCO 2 it is expressed to a curve of binding of carbonic acid. This curve binding of carbonic acid is graphically represented as follows: pCO 2 the quantity of percents by volume of carbonic acid in blood — on ordinate axis is postponed on abscissa axis, and. The curve of binding of carbonic acid is an indicator of size of an alkaline reserve of blood. The alkaline reserve of blood represents that number of CO 2 , a cut the blood plasma at pCO is capable to connect 2 , equal 40 mm of mercury. This size is similar to the size of standard bicarbonate (in mekv/l) on condition of full saturation of hemoglobin of blood oxygen (oxyhemoglobin = 100%) at a temperature of 38 °. True bicarbonates of blood represent concentration of HCOO anions 3 - (in mekv/l) in fiziol, conditions. At healthy faces the amount of true and standard bicarbonates is equal and makes apprx. 27 mekv/l or 60 about. % with fluctuations 23 — 33 mekv/l or respectively 52 — 73 about. %. At children these indicators lower and make respectively 21 — 27 mekv/l or 47 — 60 about. %. Concentration of bicarbonates of blood significantly increases at a metabolic alkalosis and to a lesser extent at respiratory acidosis. Decrease in concentration of bicarbonates is observed at a metabolic acidosis and a respiratory alkalosis. Diagnostic value of concentration of bicarbonates of blood consists first of all in establishment of respiratory or metabolic nature of disturbances To. - y. river. This indicator significantly changes at metabolic shifts and is insignificant at respiratory.

Definition of concentration of both true, and standard bicarbonates of blood is made by means of the nomograms constructed on the basis of Genderson's equation — Gasselbalkh, the best of which is Siggor-Andersen's nomogram.

For assessment To. - y. the river exists one more indicator — concentration of the buffer bases — Centuries. The quantity of B B at healthy faces at rest makes 44,4 mekv/l. In In the hl consists. obr. from bicarbonate anions and anions of protein. Change of size B B reflects extent of metabolic shifts. At metabolic frustration the VV level is sharply broken whereas at respiratory disturbances shifts of B B are insignificant. As fluctuations of size VV and at healthy faces are very considerable, the diagnostic value of this indicator is small. Often it is impossible to differentiate the nature of disturbance To. - y. river (metabolic or respiratory). Size VV in reference conditions (pH 7,38; pCO 2 40 mm of mercury.; -38 °) carries the name of the normal buffer bases (NBB). The indicator characterizing To. - y. the river, is also surplus of the buffer bases — VE. This indicator reflects the shift of the titrable buffer bases in relation to NBB. Definition of VE can be carried out by method of titration of blood under the actual conditions and after its reduction to reference conditions. This technique is very labor-consuming. In practice of VE is determined by Siggor-Andersen's nomogram. If VE is lowered, then the indicator gets a negative sign, at increase — positive. At rest at healthy faces of VE fluctuates from — 2,4 to + 2,3 mekv/l. At pathology of value of this indicator fluctuate within +30 — 30 mekv/l. The VE positive value indicates a shortcoming nonvolatile to - t or surplus of the bases, and negative value of an indicator — surplus nonvolatile to - t or deficit of the bases. The greatest shifts of VE are observed at metabolic disturbances To. - y. river. At a metabolic acidosis the indicator of VE has a negative sign (deficit of the buffer bases), and at a metabolic alkalosis surplus of the buffer bases is noted, and size VE has a positive sign. At respiratory shifts of VE changes slightly: at acidosis it is raised, and at an alkalosis — is reduced.

The indicator of VE is close to an indicator of true and standard bicarbonates. Distinction consists that VE reflects the shift of the buffer bases of buffer systems, and true bicarbonates — only bicarbonate ions.

Clinical value of indicators of acid-base equilibrium

Indicators To. - y. rubles, or in this case the acid-base state (ABS), are important a wedge, indicators of a homeostasis. Recognition of disturbances of KShchS is carried out in clinic by means of a number of indicators: pH of blood, pCO 2 , SB (standard bicarbonate, i.e. concentration of bicarbonate in the capillary blood oxygenated), VE (surplus of the bases), and also pH of urine and contents in it ketone bodies. If pCO 2 arterial blood confirms respiratory disturbances of KShchS, other indicators reflect metabolic disturbances. Lab. the data characterizing KShchS should be compared about a wedge, a picture of a disease. Development acidosis (see) and alkalosis (see) it is characterized by both respiratory, and metabolic disturbances To. - y. river; these states can pass one into another under certain conditions (inadequate therapy, etc.).

Respiratory acidosis arises at sharply reduced alveolar ventilation. It is observed in all cases of a delay in an organism of CO 2 , i.e. at hypercapnias (see), accompanying asphyxia, pneumonia, hypostasis, emphysema, an atelectasis of lungs, at poisoning with the drugs oppressing a respiratory center (barbiturates, morphine, phosphoric connections, etc.), the inadequate managed breath, pain after operations on bodies of chest and belly cavities.

Respiratory alkalosis arises at sharply strengthened ventilation of the lungs which is followed by bystry removal from an organism of CO 2 and development hypocapnies (see) — pCO 2 lower than 23 mm of mercury. It is observed at different types of an asthma, at inhalation of a light air at big height, at damage of a brain (an inflammation, an injury, a tumor), at a hyperthermia, at the inadequate managed breath.

Metabolic acidosis — the most frequent and severe form of disturbances of KShchS. It develops at starvation, heavy physical. to work, at diseases went. - kish. a path (a stenosis, fistulas, impassability of intestines, a ponosa), at the expressed hyperthyroidism, at poisonings to-tami (e.g., acetic, boric) and salicylates, at shocks (cardiogenic, traumatic, burn, operational, hemorrhagic), a collapse, koma (diabetic, azotemic, uraemic), at massive transfusions it is long the stored citrated blood. The metabolic acidosis at children since alkaline reserves at them are limited is especially hard shown. The metabolic acidosis can be complicated by respiratory. Damage of kidneys develops at disturbances of secretion of hydrogen ions and ammonia, and also a reabsorption of bicarbonate and sodium. Compensation happens first of all due to dilution excessive to - t the extracellular liquid (autogemodilyution) containing sodium bicarbonate. An active role is played by the proteins absorbing hydrogen ions in exchange for sodium and potassium in this connection can develop hyperpotassemia (see). An important compensatory role is played by a hyperventilation — at its easing the dekompensirovanny form of acidosis can develop. The role of kidneys is insignificant.

Metabolic alkalosis meets quite often at the diseases connected with reception of high doses of alkaline solutions (e.g., at heartburn); at introduction of large amounts of sodium bicarbonate (e.g., at a renal failure, at loss by an organism of chlorine — a gipokhloremichesky alkalosis); at a lack of plasma and blood cells of potassium (a gipokaliyemichesky alkalosis); as a result of oppression of reabsorbtsionny function of kidneys. This state is observed at vomitings, intestinal fistulas, toxicoses of pregnancy, supersecretion of steroid hormones etc.

KShchS at traumatic shock is characterized by a metabolic acidosis which can pass afterwards into a metabolic alkalosis that considerably worsens a state victim — dissociation of oxyhemoglobin is at a loss, it is broken microcirculation, develops hypopotassemia (see). Loss of large amounts of blood causes development of a metabolic acidosis. At burns as a result of a plasmorrhea, dehydration, a hypoproteinemia, disturbances of water and electrolytic balance the metabolic acidosis develops. At a hepatic coma the respiratory alkalosis takes place, then (in case of strengthening of circulator frustration) it Is replaced by a metabolic acidosis. At hron, the pulmonary diseases which are followed by a hyperventilation and consequently, and a hypocapny, the respiratory alkalosis which then is replaced by a metabolic acidosis develops.

Owing to hron, renal failures there is also a metabolic acidosis. The peptic ulcer of a stomach which is followed by vomiting, hepatitis, pancreatitis, colitis is complicated by a metabolic acidosis; a pyloric stenosis — a metabolic alkalosis in connection with a hypochloraemia; intestinal impassability — a tissue acidosis as a result of disintegration of proteins, loss of sodium and dehydration; highly located outside fistulas — a metabolic alkalosis (loss of chlorides), low located — a metabolic acidosis (loss of alkalis). The diabetes mellitus is characterized by a diabetic metabolic acidosis: in blood ketone bodies, and in urine — acetone are defined. Treatment of disturbances To. - y. river — see. Alkalosis , Acidosis .

A technique of determination of the parameters characterizing acid-base equilibrium

Indicators To. - y. rubles are defined on the device micro-Astrup or domestic AZIV-1. At this technique only 0,1 ml of capillary blood are required. The analysis takes only 3 — 5 min. after capture of a blood sample. At the same time the sizes pH, pCO are defined 2 , standard and true bicarbonates, surplus of the buffer bases, the buffer bases and the general carbonic acid of a blood plasma, i.e. are investigated all parameters K. - y. river of blood (see tab. 1).

The blood of the patient taken in the glass capillary which is washed out by heparin solution is soaked up by the special device in a capillary of a glass electrode. This capillary with blood is entered into the camera of a calomel electrode with saturated solution of potassium chloride. Temperature of electrodes is maintained by the thermostat at the level of 37 °. Each blood sample is divided into 3 parts. pH is measured in one portion, two others are saturated in the ekvilibrovochny camera within 3 min. with mixes O 2 and CO 2 in advance famous structure. The last move in the camera from cylinders through humidifiers. In one of the cylinders pCO 2 it is lower than 40 mm of mercury., in another, on the contrary — above. In the analysis of each blood sample receive 3 pH values — at true, low and high pCO 2 .

Siggor-Andersen's Nomogram: points And yes In correspond to preset values of pCO 2  ; a point of F — the place of crossing of the perpendicular recovered from a point on abscissa axis, the corresponding size of urgent pH (7,135) with direct AV. The perpendicular lowered from a point of F on ordinate axis crosses it in the point characterizing an indicator of urgent pCO 2 (54 mm of mercury.). Points of intersection of the AV line and its continuations with schedules of standard bicarbonate (I), the buffer bases (II) and excess of the bases (III) — points of D, E and S — characterize specific sizes of these indicators at preset values of pCO 2 . On abscissa axis — indicators of urgent pH, on ordinate axis — indicators of urgent pCO 2 in mm of mercury.

By an ekvilibratsionny method of Astrup size of urgent pCO 2 determine by urgent pH and two other sizes pH at precisely set pCO 2 (above and below datum level) according to Siggor-Andersen's nomogram. On schedule (fig.) of a point And yes In, corresponding to two sizes pCO 2 (above and below datum level), connect a straight line. Through the point on an abscissa corresponding to the size of urgent pH draw the line parallel to ordinate, before crossing with direct AV and find a point of F. The perpendicular lowered from a point of F by ordinate hits the nail corresponding to the size of urgent pCO 2 . Points of intersection of the AV line and its continuations from a curve of standard bicarbonate and excess of the bases allow to define the corresponding indicators for the studied portion of blood.

More exact, but demanding special adaptation, direct definition of pCO is 2 by means of a special electrode; general maintenance of CO 2 in blood it is possible to determine by Van-Slayka's method, volume or manometrical (see. Van-Slayka methods ), by Conway's method (see. Conway method ) or automatic colorimetric method. Size of the general maintenance of CO 2 CO can be calculated by a formula 2 obshch = [HCO 3 - ] + pCO 2 • 0,0301 on the basis of data of pCO 2 and [HCO 3 - ] or according to Siggor-Andersen's nomogram in sizes pH and pCO 2 . An alkaline reserve (ability of blood to connect CO 2 ) define in the same ways, as the general carbonic acid, but in the conditions of an equilibration of plasma at pCO 2 , equal 40 mm of mercury. Siggor-Andersen's nomogram is most convenient for definition of an alkaline reserve.

Devices for definition of acid-base equilibrium

the Main device for definition To. - y. the river is the pH-meter intended for electrochemical measurement of pH of the environment by means of glass ion-selective electrode (see). rn-Metr enters all modern analyzers K. - y. the river and blood gases which also the gas-selection electrode of Severinkhauz for direct definition of pCO enters 2 . Majority of modern analyzers K. - y. the river provides also direct measurement of pO 2 Wednesdays by means of the gas-selection electrode of Clark. Though pO 2 also is not a direct indicator To. - y. the river, its measurement gives the chance more precisely to calculate VE, and also to estimate the reason and the nature of changes To. - y. river. Important advantage of modern methods of a research K. - y. the river is speed of the analysis and a possibility of use of microamounts of capillary blood instead of arterial (compliance of their indicators is proved for all states at which there is no essential disturbance of peripheric circulation).

The domestic medical industry AZIV-2 is issued. It is intended for direct measurement of the size pH and partial pressure of oxygen (pO 2 ) at a research K. - y. river in blood samples and others biol, liquids. The device has unitized construction, consists of pH-meter and the block of a tonometer with primary converters and is placed on a mobile table. rn-Metr provides: two ranges of measurement of pH — from 4 to 9 units of pH with absolute error of measurement + 0,1 units of pH and from 6,8 to 7,8 units of pH with absolute error of measurement + 0,02 units of pH; three ranges of measurement of pO 2 — from 0 to 100 mm of mercury. with the main error brought to an upper limit of measurement + 2,5%, from 0 to 200 mm of mercury. with a margin error + 2,5% and from 0 to 1000 mm of mercury. with a margin error + 5%. Inclusion of pH-meter and choice of required ranges of measurement of pH and pO 2 are made by means of the keyboard switch. The block of a tonometer consists of a glass ion-selective electrode of pH, a reference electrode and primary pO converter 2 . Here the thermostat and the electroblock which automatically switches-off the vibrator serving for saturation of a blood sample as gas mixtures belong. The system of thermostating provides maintenance of set-point temperature of the thermostat 37 + 0,2 °, primary pO converter 2 , glass electrode and reference electrode. Temperature of blood samples at a tonometrirovaniye is maintained by a constant thanks to immersion of vessels in vessels directly in the thermostat. The gas system is intended for supply of the gas mixtures moistened and warmed up to 37 ° in vessels in which the equilibration of blood with these mixes, and in the camera of primary pO converter is made 2 — for graduation. Gas mixtures in cylinders shall have such structures. Gas I: CO 2 — 4 ± 0,2%, O 2 — 21 ± 0,2%, the rest — N 2  ; gas II: CO 2 — 8 ± 0,2%, 02 — 21 ± 0,2%, the rest — N 2 . Primary pO converter 2 and electrodes for measurement of pH are connected directly to the instrument sockets of pH-meter located on its back wall and designated according to «pO 2  », «pH -ism.  » and «pH vsp.  ». Definition of pCO 2 it is made by an indirect method of interpolation with use of the nomogram of Siggor-Andersen. Are determined by the nomogram as well metabolic indicators To. - y. river. The volume of test necessary for the analysis does not exceed 0,04 ml at measurement of pH and 0,2 ml at measurement of pO 2 .

A gas analyzer of AVL-937-S of the Swiss firm «AVL» for definition To. - y. the river has electrodes for direct measurement of pH, pCO 2 and pO 2 in a blood sample only 0,02 — 0,04 ml. The computer which is a part of the device automatically counts and gives out in the printed look, in addition to the sizes pH, pCO 2 and pO 2 , as well sizes BE, BB, standard bicarbonate, general content of carbon dioxide gas, indicator of hemoglobin (%Hb) and oxygen saturation of blood. Electrode of pO 2 represents compound wire system. It is distinguished by very high sensitivity and accuracy of measurements with the broad range of pO 2 , what is reached thanks to small oxygen absorption by an electrode. There is an automatic signaling device of failure of electrodes. One of the main advantages of the device is existence of system of mixing and calibration of gases. The feeding gases represent the free air given by the compressor with automatic pressure retention in a receiver and standard carbon dioxide gas from a cylinder. Thus, need to have special cylinders with calibration gases that very much simplifies service of the device disappears. Also need of use free from O disappears 2 gases or liquids for the purpose of zero calibration of an electrode of pO 2 .

The most modern device for definition To. - y. the river and blood gases the ABL 2 Acid-Base Laboratory device of the Danish firm «Radiometer» is. It has all listed above advantages. Besides, all process of the analysis — from the moment of receipt in the device of a microprobe of blood before obtaining digital information on all major sizes K. - y. the river and blood gases on the standard form — it is completely automated. The device is considered a sample of ergonomically perfect device.

Diagnosis of disturbances of acid-base equilibrium

in the Main way of diagnosis of disturbances To. - y. the river of an organism is a blood analysis one of the methods described above. The analysis of others biol, substrates (urine, erythrocytes, cerebrospinal liquid) is for this purpose undertaken less often. Changes of indicators To. - y. the rubles of blood corresponding a nek-eye (simple) disturbances To. - y. rubles, are presented in tab. 2. Apparently from the table, the sizes pH, pCO in itself 2 and VE not always give the chance to differentiate a number of disturbances To. - y. river E.g., decrease in pCO 2 and VE at a normal amount of pH can take place both at the compensated metabolic acidosis, and at the compensated respiratory alkalosis.

An essential lack of widespread methods of assessment To. - y. the river of an organism consists in an identification To. - y. river of in vitro blood (at a lab. a research) and in vivo (in a complete organism). In some cases this identification leads to essential mistakes in diagnosis of disturbances To. - y. river. So, e.g., at a respiratory acidosis of in vivo the ions of bicarbonate which are formed preferential in blood partially pass into intersticial liquid that, naturally, there cannot be in vitro. At a lab. a blood analysis this process is expressed by decrease in VE and formally interpreted as a metabolic acidosis though increase in contents nonvolatile to - t in an organism (including and in blood) at a respiratory acidosis does not happen. For the similar reasons compensatory reactions at disturbances To. - y. rubles (e.g., strengthening of ions of bicarbonate in plasma owing to activation of their reabsorption in renal tubules at a respiratory acidosis) look as patol, processes (in this case as a metabolic alkalosis).

Difficulties of this sort were substantially overcome by introduction of new criteria of a metabolic component K. - y. river (VE of extracellular liquid, and also partly concentration of bicarbonate of plasma) and studying of quantitative dependences between indicators To. - y. river of blood at various accurately certain disturbances To. - y. river of an organism. So, e.g., the data characterizing an acute respiratory acidosis were received at short-term inhalation of the gas mixtures supporting CO 2 , or so-called diffusion breath; hron, the respiratory alkalosis comes to light at people, is long living in conditions of highlands; hron, a metabolic acidosis — at patients with a renal failure or dekompensirovanny diabetes; hron, a respiratory acidosis — at patients with pulmonary insufficiency etc.

Results of similar researches allowed to define borders of changes of indicators To. - y. river, the most probable at the disturbance given it. However at all importance of results of a research K. - y. river of blood (especially in dynamics of a disease) crucial importance for diagnosis of disturbances To. - y. the river gets comparison them with data a wedge, researches.


Table 1. INDICATORS of ACID-BASE EQUILIBRIUM of the ORGANISM AND THEIR NORMAL AMOUNTS (according to F. I. Komarov and soavt., 1976)


Table 2. INDICATORS of ACID-BASE EQUILIBRIUM of BLOOD AT SIMPLE FORMS of ITS DISTURBANCES (DIAGRAMMATIC REPRESENTATION)


Symbols: &&&& nbsp;nbsp;#8595;nbsp;— &&&снижение;nbsp;#8593;nbsp;— increase;   = normal amount; the number of arrows corresponds to degree (or expressivenesses) changes of acid-base equilibrium.



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V. M. Bogolyubov; Ya. A. Rudayev (rubbed.), V. M. Yurevich (tekhn.).

Яндекс.Метрика