Dr.D Panda – Major Intra & Extra Cellular Electrolytes

MAJOR INTRA AND EXTRA CELLULAR ELECTROLYTES

There are a number of inorganic and organic ions present in the body fluids whose concentrations in various fluid compartments are ionically balanced by the help of osmotic pressure and pH in our body. The various fluid compartments of the body are; i) ii)

Intra-cellular fluid ( fluid present inside the cell – cytoplasm ) Extra-cellular fluid – (a) Interstitial fluid ( fluid present between the cells ) and (b) Plasma fluid ( fluid present within the blood vascular system ).

The intracellular compartment contains slightly less than two-thirds by volume of fluid where as the remaining third is distributed in the extracellular fluid.

The major electrolytes found in our body are; Sodium (Na+), Potassium (K+), Calcium (Ca++), Magnesium (Mg++), --Bicarbonate (HCO3 ), Chloride (Cl ), Phosphate (HPO4 ) and Sulphate (SO4 ) Out of the above electrolytes, the major cation in extracellular fluids is sodium and the major anion is chloride where as in intracellular fluid, the major cation is potassium and the major anion is phosphate. The electrolyte concentration in the body fluids of a healthy person is almost constant. But it becomes inbalanced only when the person undergoes surgery or remains ill or some other undesirable conditions for a prolonged period. Under such conditions, external administration of electrolyte replacement therapy is carried out.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

Composition of Body Fluids : A 70 kg male has 40-42 litres (approx..60% of body weight) of fluid in the following distribution; Intracellular fluid (ICF)

= 25 – 28 Litres (approx..40-45% of body weight)

Extracellular fluid (ECF) = 14-16 Litres [ Interstitial 10-12 Ltrs (12-15% of BW) and Intravascular 3-5 Ltrs (4-5% of BW) ] Total blood volume

= 5 Litres (2 litres consist of RBCs)

The three compartments (intracellular fluid, interstitial fluid and plasma or vascular fluid) are separated from each other by membranes that are permeable to water and many organic and inorganic solutes. They are nearly impermeable to macromolecules, i.e. proteins and selectively permeable to certain ions like Na+, K+ and Mg++. Hence, the fluid in each compartment is ionically balanced by maintaining this permeability criteria. Thus, sodium and chloride are found in plasma and interstitial fluids, while potassium, magnesium and phosphate are found in the intracellular fluid. Regulation of Sodium Balance : Influence of Aldosterone and Angiotensin II [Aldosterone is a steroid hormone (mineralocorticoid family) produced by the outer section (zona glomerulosa) of the adrenal cortex in the adrenal gland. Angiotensin is a peptide hormone that causes vasoconstriction and a subsequent increase in blood pressure. It is part of the renin-angiotensin system, which is a major target for drugs that lower blood pressure. Angiotensin also stimulates the release of aldosterone. Angiotensin is derived from the precursor molecule angiotensinogen, a serum globulin produced in the liver. Angiotensin I is formed by the action of renin on angiotensinogen. Angiotensin I is converted to Angiotensin II through removal of two C-terminal residues by the enzyme angiotensin-converting enzyme (ACE), primarily through ACE within the lungs (but also present in endothelial and kidney epithelial cells). Angiotensin II acts as an endocrine, autocrine/paracrine, and intracrine hormone.] When aldosterone secretion is high, nearly all the filtered sodium is reabsorbed in the distal convoluted tubule (distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting duct system, partly responsible for the regulation of potassium, sodium, calcium, and pH) and the collecting duct (collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter). The most important trigger for the release of aldosterone is the renin-angiotensin mechanism, initiated in response to sympathetic stimulation, decrease in filtrate osmolality, or decreased blood pressure.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

Regulation of Potassium Balance : Potassium is critical to the maintenance of the membrane potential of neurons and muscle cells, and is a buffer that compensates for shifts of hydrogen ions in or out of the cell. Potassium balance is chiefly regulated by renal mechanisms, which control the amount of potassium secreted into the filtrate. Blood plasma levels of potassium are the most important factor regulating potassium secretion. Aldosterone influences potassium secretion, since potassium secretion is simultaneously enhanced when sodium reabsorption increases. Regulation of Calcium and Phosphate Balance : Calcium ion levels are closely regulated by parathyroid hormone and calcitonin; about 98% is reabsorbed. Parathyroid hormone is released when blood calcium levels decline, and targets the bones, small intestine, and kidneys. Calcitonin is an antagonist to parathyroid hormone, and is released when blood calcium rises, targeting bone. Regulation of Anions : Chloride is the major anion reabsorbed with sodium, and helps maintain the osmotic pressure of the blood. Influence of Other Hormones : Estrogens are chemically similar to aldosterone, and enhance reabsorption of salt by the renal tubules. Progesterone promotes Na+ and water loss, apparently by antagonizing the effects of aldosterone. Glucocorticoids enhance tubular reabsorption of Na+, but also increase the glomerular filtration rate. At high levels reabsorption dominates, which promotes edema [ edema is a condition in which fluid gets accumulated in the interstitial space because of low osmotic pressure ].

Physiological Ions Some of the important functions being carried out by the electrolytes can be summarised as follows; i)

To control osmosis of water between various body compartments.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

ii) iii)

To maintain the acid-base balance required for normal cellular activities. To control the secretion of some hormones and neurotransmitters.

SODIUM (Na+) It is a most abundant extracellular ion which constitutes about 90% of extracellular cations. It is responsible for normal hydration and osmotic pressure. Normal plasma sodium content is 136-142 mEq/litre. The sodium level in the blood is controlled by aldosterone ( an antidiuretic hormone - ADH). Normally, kidney excretes the excess of sodium and regulate the sodium content in the body. The important functions carried out by sodium ions in our body are; a) It regulates the acid-base equilibrium in association with chloride and bicarbonate. b) Helps in maintaining osmotic pressure of various body fluids and thereby, protecting the body against excessive fluid loss. c) Preserves normal irritability of the muscles and permeability of the cells. d) Plays important role in transmission of nerve impulses.

Low sodium level (hyponatremia) in serum occurs due to the following conditions; i) ii) iii) iv)

Diarrhoea and vomiting. Excessive excretion of sodium in metabolic acidosis. Excessive urination as in case of diabetes insipidus. Decreased secretion of aldosterone (an antidiuretic hormone) in addison’s disease (chronic endocrine disorder in which the adrenal glands do not produce sufficient steroid hormones - glucocorticoids and often mineralocorticoids).

[ Difference between diabetes insipidus and diabetis mellitus - diabetes mellitus and diabetes insipidus are two entirely different conditions with unrelated mechanisms. Both cause production of large amounts of urine (polyuria) but the ‘diabetes insipidus’ is either a problem with the production of antidiuretic hormone (central diabetes insipidus) or kidney's response to antidiuretic hormone (nephrogenic diabetes insipidus), whereas ‘diabetes mellitus’ causes polyuria via a process called osmotic diuresis, due to the high blood sugar leaking into the urine and taking excess water along with it.] The symptoms of hyponatremia include muscular weakness, dizziness (a psycho-disorder of non-specific feeling of foolishness mostly due to insufficient blood supply to the brain), headache, hypotension, tachycardia (heart rate is more than normal – exceeds 100 beats per minute), etc. High sodium level (hypernatremia) in serum takes place due to the following conditions; i)

Severe dehydration. ii) Hyperadrenalism – abnormal functioning of adrenal gland (cushing’s syndrome - the signs and symptoms associated with prolonged

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

exposure to inappropriately high levels of the hormone cortisol), iii) Certain types of brain damage, iv) Excessive treatment with sodium salts. The symptoms of hypernatremia include excessive thirst, fatigue (feeling of tiredness), restlessness, agitation, coma (a state of unconsciousness lasting for more than six hours), etc.

POTASSIUM (K+) It is a most abundant cation in intracellular fluid whose concentration in ICF is about 23 times more than that of the extra cellular fluid (ECF). Normal plasma concentration of potassium is about 3.8 – 5.0 mEq/litre. Its daily requirement is about 1.5 to 4.5 gm.The sources of potassium in food are available from milk, certain vegetables, meat, whole grains, etc. It rapidly gets absorbed from the diet from G.I. tract and rapidly excreted through kidneys. Generally, its deficiency does not take place only except in certain pathological conditions. The excretion of potassium through kidney gets influenced by changes in acid-base balance and activity of adrenal cortex. Its important functions include; i) ii) iii)

iv) v)

Helps in contraction of cardiac muscles. Maintains electrolyte composition of various body fluids. Helps to regulate pH by exchange against hydrogen ions (Potassium interacts in very important ways with H+ ; the two share a reciprocal relationship. When H+ concentration is elevated in the ECF, as occurs in metabolic acidosis, H+ moves into the cell, and K+ moves out. This exchange allows H+ access to the intracellular protein buffers, which can minimize changes in pH. When H+ concentration is decreased (as in metabolic alkalosis), H+ moves out of the cell, and K+ moves in, which can result in a hypokalemic state.). Helps in transmission of nerve impulses. Takes part in many biochemical activities within the cells.

Elevated serum potassium level (hyperkalemia) is marked in the patients suffering from renal failure, advanced dehydration, addison’s disease, cardiac depression, CNS depression, etc. Hyperkalemia causes bradycardia, poor heart sound, peripheral vascular collapse (involves outlying arteries and veins in the body where they fail to maintain the supply of oxygen and other nutrients to the tissues and to remove the carbon dioxide and other metabolites from them), cardiac arrest, weakness of respiratory muscles, etc. Low serum potassium level (hypokalemia) is marked in the patients having malnutrition, gastro-intestinal losses in diarrhoea, metabolic alkalosis, heart diseases, etc.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

Hypokalemia causes changes in myocardial functions, flaccid and feeble muscles (soft and weak muscles), and low blood pressure.

CALCIUM (Ca++) It is mainly found in the bones and largely available in the extra-cellular fluid compartment. Its total availability in our body is about 20-22gms per kg of body weight and its daily requirement is about 0.8 to 1.0gm. The dietary sources of calcium are milk, cheese, green vegetables, eggs, fishes, etc. The normal calcium concentration in plasma is about 8.5 to 10.5 mg / 100ml out of which about 4.2 to 5.5 mg / 100ml are present in plasma proteins. The plasma calcium concentration is maintained by parathyroid hormone and calcitonin. A small quantity of calcium is complexed with citrate and phosphate and the remaining quantity is circulated in the blood stream in ionised form. This ionised calcium plays vital role in the functioning of nerves and muscles. Convulsions may take place due to less availability of ionised calcium and cardiac function disturbances may occur in case of high concentration of ionised calcium. The calcium is mainly excreted from our body through sweating, urination and faeces. Some important functions of calcium in our body includes; i) ii) iii) iv)

It hardens the bones by association with vitamin-D and phosphorus. Takes part in coagulation of blood. Involves in nerve impulse propagation and nerve contraction. Helps in releasing acetylcholine from preganglionic nerve terminals.

Low calcium level in our body (Hypocalcemia) is caused due to alkalosis, blood transfusions, renal failure, vitamin D deficiency, bypass surgery, intake of diuretic drugs, pancreatitis, etc. and the symptoms of calcium deficiency includes hypotension, general weakness, muscle spasms, heart failure, etc. High level of calcium (Hypercalcemia) is caused due to hyper-parathyroidism, Ca++ release from bones (osteo-tumors), excess Vitamin D, alkalosis, treatment with thiazide diuretics, etc. and the symptoms include hypotension, dehydration, polyuria, weakness, pancreatitis, renal stones, etc. MAGNESIUM (Mg++) It is the second most common intracellular electrolyte and is most abundant cation in our body. Its normal body content is about 24-26gms ( 12-13gms in bones along with phosphorus, 10-11gms in intracellular fluid and 0.25 - 0.30gms in extracellular fluid ). Its excretion through urine is very less (3.5 – 4.5 µmol / day).

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

Daily requirement of magnesium is about 350mg which can be supplemented from various foods like nuts, soyabeans, whole grains, sea foods, etc. Its main functions include; i) ii) iii)

Activates the enzymes which are involved in carbohydrate and protein metabolism. Takes part in neural transmission, myocardial functions and neuro-muscular activities. Required for operational activities of Na+/K+ - ATPase pump.

Excessive losses of dietary magnesium (Hypomagnesemia) takes place if the patient suffers from malabsorption, diarrhoea or chronic alcoholism. Hypomagnesemia is characterised by weakness, irritability, convulsions (rapid and repeated contraction and relaxation of body muscles resulting in uncontrolled shaking of body – epileptic seizures), confusion, anorexia (poor appetite), nausea (feeling of discomfort in upper stomach) and cardiac arrhythmias (functional abnormalities in myocardium). Under certain conditions like addison’s disease, acute diabetic acidosis, severe dehydration, or renal failure, the magnesium level increases (Hypermagnesemia) which is characterised by slurred speech (jumbling of words while talking – improper functioning of muscles which are used for talking), drowsiness, impaired muscular coordination, hypotension, cardiac arrest, etc. -

BICARBONATE ( HCO3 ) It is the second most prevalent anion in the extracellular fluid compartments. Alongwith carbonic acid, it acts as one of the most important buffer system in our body by maintaining the physiological acid – base balance.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

[ Major Concentrations of Electrolytes that Affect Acid – Base Balance ( m.Eq/ L.) ]

A lack of bicarbonate causes metabolic acidosis and an excess causes metabolic alkalosis. (Already discussed in previous chapter ) Metabolic acidosis is an ECF deficit of bicarbonate caused by conditions that result in a loss of bicarbonate or an increase in fixed acids. Metabolic alkalosis is an ECF excess of HC03 – caused by conditions resulting in excess base because of loss of H+, reabsorption of HC03 -,or loss of other ions (i.e., chloride, sodium). -

CHLORIDE ( Cl ) It is one of the major extracellular anion mostly responsible for maintaining proper hydration, osmotic pressure, and normal cation-anion balance in the vascular and interstitial fluid compartments. -

The chloride ion ( Cl ) also contributes to acid-base imbalance because it usually follows -

--

Na+ passively. An increase in Cl results in a decreased reabsorption of HC03 with Na+ in the renal tubules, which can result in a metabolic acidosis associated with hyperchloremia. -The reverse of this (increase in HC03 resulting in a decreased reabsorption of Cl with Na+) can result in a hypochloremic metabolic alkalosis. Food is the main source of chloride, with the anion being completely absorbed from the intestinal tract. Chloride is removed frm the blood by glomerular filtration and is reabsorbed by the kidney tubules. [Glomerular Filtration : In the kidney, a tubular structure called the nephron filters blood to form urine. At the beginning of the nephron, the glomerulus is a network (tuft) of capillaries

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

that performs the first step of filtering blood. The glomerulus is surrounded by Bowman's capsule. The blood plasma is filtered through the capillaries of the glomerulus into the Bowman's capsule. The Bowman's capsule empties the filtrate into a tubule that is also part of the nephron. A glomerulus receives its blood supply from an afferent arteriole of the renal circulation. Unlike most other capillary beds, the glomerulus drains into an efferent arteriole rather than a venule. The resistance of these arterioles results in high pressure within the glomerulus, aiding the process of ultrafiltration, where fluids and soluble materials in the blood are forced out of the capillaries and into Bowman's capsule. A glomerulus and its surrounding Bowman's capsule constitute a renal corpuscle, the basic filtration unit of the kidney. The rate at which blood is filtered through all of the glomeruli, and thus the measure of the overall renal function, is the glomerular filtration rate (GFR).] Hypochloremia is caused due to; i)

ii)

iii)

Salt-losing nephritis (inflammation of the kidney) alongwith chronic pyelonephritis (inflammation of the kidney and its pelvis), leading to a lack of tubular reabsorption of chloride. Metabolic acidosis (as found in diabetis mellitus and renal failure), causing either excessive production or diminished excretion of acids leading to the replacement of chloride by acetoacetate and phosphate. Prolonged vomiting with loss of chloride as gastric HCl.

Hyperchloremia takes place due to dehydration, decreased renal blood flow found with congestive heart failure, severe renal damage, and excessive chloride intake. --

PHOSPHATE ( as HPO4 ) It is the principal anion of the intracellular fluid compartment. Normal plasma phosphate concentration is 1.7 – 2.6 mEq/L. Its various functions include; i) ii) iii) iv) v)

Essential for proper calcium metabolism. Essential for normal bone and tooth development since it is a component of hydroxyapatite (main calcium salt found in bones and teeth). The phosphoric acid anhydride linkage is the body’s means of storing ATP. Plays vital role in buffering systems of the body. Plays an important regulatory role in erythrocyte-glucose metabolism.

The main dietary sources of phosphate are milk products, whole grains, legumes, nuts, etc. Serum phosphate levels usually correlate with serum calcium values. When there is change in calcium concentration, the serum phosphate is also changes to either higher than normal (hyperphosphatemia) or lower than normal (hypophosphatemia). Hyperphosphatemia condition occurs due to hypervitaminosis D (which increases intestinal phosphate absorption alongwith calcium), renal failure (due to inability to excrete phosphate

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

into the urine), and hypoparathyroidism (lack of parathyroid hormone permits renal tubular reabsorption of phosphate and a rise in serum phosphate). The complication that arises due to hyperphosphatemia is the formation of phosphatic urinary calculi (kidney stone) which may cause kidney damage. Hypophosphatemia occurs due to vitamin D deficiency (rickets), hyperparathyroidism, lack of phosphate reabsorption by kidney tubule due to various infections and long-term therapy with aluminium hydroxide gel antacid. Hypophosphatemia causes marked alterations in erythrocyte metabolism, resulting in decreases in erythrocyte glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P), 2,3-diphosphoglycerate (2,3-DPG), 3-phosphoglyceric acid (3PG), phosphoenolpyruvate (PEP), and adenosyl triphosphate (ATP). --

SULPHATE (SO4 ) It is present in very minute quantities in both plasma and interstitial fluid (extracellular fluid). The main dietary sources of sulphate are animal and plant proteins having sulphur containing amino acids (cysteine and methionine – sulphate ions are derived from the metabolism of these amino acids). Its main functions include; i) ii)

Takes part in detoxification mechanism (particularly sulphur containing compounds) Very much helpful in tissue respiration [particularly –SH group (sulfhydryl/thiol group) containing compounds].

ACID – BASE BALANCE Acids (carbonic acid from carbon dioxide and lactic acid from anaerobic metabolism) are constantly being produced during metabolism. Since, most of the metabolic reactions occur only within a very narrow pH range (7.38 – 7.42), the body utililizes several efficient buffer systems. Body fluids have balanced quantities of acids and bases which are well regulated by complicated mechanisms. This balancing of acids and bases within the body is very much essential because the biochemical reactions taking place in the living systems are very sensitive to even small changes in acidity or alkalinity. For example, → Low pH value in the stomach provides an environment where enzyme pepsin functions well which is involved in the digestion of dietary proteins. → Saliva is having a pH range of 5.4 – 7.4 which provides the environment best suited for the functioning of ptyalin, an enzyme present in saliva which digests the carbohydrates.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

In this way, the pH of the various body fluids are naturally maintained within the required ranges, some of which are mentioned below; Body Fluids Gastric Juice Saliva Blood Urine Bile Semen

pH Ranges 1.5 – 3.5 5.4 – 7.5 7.4 – 7.5 4.5 – 8.0 6.0 – 8.5 7.2 – 7.6

The pH of the body fluids are always maintained due to presence of various buffer systems in our body. Two of the major buffer systems in the body are bicarbonate/carbonic acid (HCO3/H2CO3) found in the plasma and kidneys and monohydrogen phosphate / dihydrogen phosphate (HPO4-2/H2PO4-) found in the cells and kidneys. Also, the haemoglobin(Hb) buffer system present in the red blood cells is the most effective single system for buffering the carbonic acid produced during metabolic processes. The main function of the buffer system is to prevent drastic changes in the pH values in the blood. However, it can be effective only when there exists some mechanisms by which excess acid or alkali can be excreted out of the body. This function is mainly carried out by the lungs and the kidneys. When respiration gets decreased, the accumulated carbon dioxide combines with water to form carbonic acid which then dissociates to release hydrogen ions and results in acidosis. CO2 + H2O → H2CO3 → H+ + HCO3 Similarly, if there is over breathing, excessive excretion of carbon dioxide takes place which leads to alkalosis. The electrolytes control the fluid imbalances in our body and apart from that, they also play a vital role in regulating the body’s acid-base balance. This balance is mainly maintained by controlling the H+ concentration in the extra-cellular fluid (normal pH range – 7.35 to 7.45) of the body. Various Buffer Systems of Body : ( I ) Carbonic acid – Bicarbonate Buffer system It is an important buffer system (occurs in plasma and kidneys) for regulating blood pH. If there is excess of H+ ion in the blood, the bicarbonate ion accepts the H+ ion to form carbonic acid and this carbonic acid further dissociates to yield carbon dioxide and water molecule. H+ + HCO3 - → H2CO3 → Strong acid

Weak base

H2O + CO2

Carbonic acid (weak acid)

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

When, there is shortage of H+ ion, the carbonic acid (another component of buffer system) ionises to release more H+ ions to maintain the pH. →

H2CO3 Carbonic acid (weak acid)

H+

HCO3 -

+

Strong acid

Weak base

Our normal metabolism process gives rise to more acids than bases. But the blood made more acidic. Therfore, the body needs more bicarbonate salt than it needs carbonic acid. (II) Phosphate Buffer System The phosphate concentration is more in the intra-cellular fluid and so, phosphate buffer system is considered to be an important regulator of pH in the cytosol. This buffer system is mainly present in the cells and kidneys. As we know, this buffer system consists of monohydrogen phosphate (HPO4-2) / dihydrogen phosphate (H2PO4-) anions, acts in a similar manner as that of carbonic acid – bicarbonate buffer system. If there is occurance of an excess of H+ ion in the presence of strong acid, the monohydrogen phosphate ion acts as a weak base by accepting the proton. HCl

Na2HPO4 → NaCl + NaH2PO4

+

Strong acid

Weak base

Salt

Weak acid

When there is presence of a strong base, the dihydrogen phosphate ion acts as a weak acid and is able to neutralise the alkaline condition. NaOH + NaH2PO4 Strong base

→ H2O + Na2HPO4

Weak acid

Weak Base

(III) Protein (Haemoglobin) Buffer System It is the most abundant buffer system in the cells and plasma. Proteins are composed of amino acids which do have atleast one carboxyl group (COOH) and one amino group (NH2). When there is occurance of excess H+ ions, the amino group acts as a base and accepts the proton. R R │

│

HOOC ─ C ─ NH2 + H+ │ H

→ HOOC

─ C ─ NH3+ │ H

While the free carboxyl group can release protons so as to neutralise an alkaline condition. R │ H2N ─ C ─ COOH │ H

R │

→

H2N ─ C ─ COO │ H

-

+ H+

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

Thus, protein is able to serve both the functions of acid and base components of a buffer system because of its amphoteric nature. At physiological pH, histidines and cysteine are considered to be the most important amino acid buffers. As haemoglobin (protein) is composed of 37 histidines in its structure, it acts as an effective physiological buffer. When CO2 enters the erythrocytes from the body cells, it rapidly combines with water to form carbonic acid in the presence of the enzyme, carbonic anhydrase. If there occurs a shortage of H+ ions in erythrocytes, the carbonic acid gets dissociated into H+ and HCO3- ions. The bicarbonate ion in plasma alongwith the plasma carbonic acid now behaves as an efficient buffer system. Breathing also plays an important role in maintaining the pH of the body fluids. CO2 + H2O

↔ H2CO3 ↔ H+

+ HCO3 –

Metabolic Acidosis & Metabolic Alkalosis The pH of normal blood ranges between 7.35 to 7.45. When the pH of blood falls below 7.35, the condition is known as metabolic acidosis, while when the pH of blood is higher than 7.45, it is known as metabolic alkalosis. Both the conditions are considered to be the primary disorders of bicarbonate (HCO3-) concentration. The metabolic acidosis takes place due to loss of HCO3- ions which may occur due to severe diarrhoea or renal dysfunction. The condition results in depression of central nervous system. The treatment of metabolic acidosis is made by administration of intravenous injection of NaHCO3. Excessive vomiting of gastric contents causes a substantial loss of hydrochloric acid and it is a cause of metabolic alkalosis. Other causes may include endocrine disorders, excessive intake of alkaline drugs, use of certain diuretics, etc. Its principal effect is the overexcitability of the CNS. Treatment of metabolic alkalosis involves the fluid therapy to replace chloride, potassium and other electrolyte deficiencies.

ELECTROLYTES USED IN REPLACEMENT THERAPY Under normal physiological conditions, the various body mechanisms are able to maintain the electrolyte balance. But under certain conditions like prolonged fever, severe vomiting or diarrhoea, there is severe loss of water and electrolytes and there is imbalance of electrolyte concentration. This loss of electrolytes can be compensated by oral / parenteral administration of appropriate concentration of required electrolytes, which is termed as replacement therapy.

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

There are two types of electrolyte solutions being used for replacement therapy, i.e. electrolyte solution for initial replacement and solution for subsequent replacement. i)

Electrolyte solution for initial replacement therapy :

It is a preparation of various electrolytes resembling the composition of electrolytes of extracellular fluid which is administered in emergency cases. The normal composition of this kind of preparations are; Sodium Chloride Bicarbonate Potassium Calcium Magnesium ii)

– 130-150 mEq/L – 98-110 mEq/L – 28-55 mEq/L – 4-12 mEq/L – 3-5 mEq/L – 2-3 mEq/L

Electrolyte solution for subsequent replacement therapy :

This type of preparation is used for subsequent treatment of electrolyte replacement as required to compensate the electrolyte losses. The normal composition of this kind of preparations are; Sodium Chloride Bicarbonate Potassium Calcium Magnesium Phosphate

– 40-120 mEq/L – 30-105 mEq/L – 16-53 mEq/L – 16-35 mEq/L – 10-15 mEq/L – 3-6 mEq/L – 0-3 mEq/L

Apart from the above combination of electrolytes preparations, some individual electrolyte preparations are also available for compensatory replacement therapy of particular electrolyte losses. Those are ; For Sodium Replacement – Sodium chloride tablets, sodium chloride solution, sodium chloride injection, sodium chloride and dextrose tablets, sodium chloride and dextrose injection, mannitol and sodium chloride injection, fructose and sodium chloride injection, Ringer’s injection (containing 147mEq/L of Na, 4 mEq/L of K, 4.5 mEq/L of Ca and 155.5 mEq/L of Cl) and Lactated Ringer’s injection (containing 130mEq/L of Na, 4 mEq/L of K, 2.7 mEq/L of Ca, 109.7 mEq/L of Cl and 27mEq/L of Lactate).

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Dr.D Panda – Major Intra & Extra Cellular Electrolytes

For Potassium Replacement – Potassium chloride tablets, Potassium chloride injection, Ringer’s injection, Lactated Ringer’s injection, Potassium gluconate tablets, Potassium gluconate Elixir, etc. For Calcium Replacement - Ringer’s injection, Lactated Ringer’s injection, Calcium gluconate tablets, Calcium gluconate injection, Calcium lactate tablets, etc.

ORAL REHYDRATION SALTS (ORS) These preparations are the mixtures of electrolytes in various compositions available in the market in powder forms, used for oral replacement therapy. Mostly, the following three formulations of ORS (approved by WHO and UNICEF) are available in the market.

Ingredients Sodium chloride Potassium chloride Sodium bicarbonate Sodium Citrate Anhyd. Glucose

Formulation - I (For 1 ltr solution) 3.5 gm 1.5 gm 2.5 gm 20.0 gm

Formulation - II (For 1 ltr solution) 3.5 gm 1.5 gm 2.9 gm 20.0 gm

Formulation - III (For 1 ltr solution) 2.6 gm 1.5 gm 2.9 gm 13.5 gm

Formulations I and II were existing since long but the formulation – III has been recently approved by WHO and UNICEF after a long clinical trial. In Formulation – III, the quantity of Sodium chloride and glucose has been reduced to increase its osmolarity so that the formulation can help in reducing the frequency of stool as well as diarrhoea.

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