Electrolytes (Major intra and extra cellular)

  • The body fluids are solutions of organic and inorganic solutes. The concentration balance of various components are maintained in order for the cell and tissues which have constant environment. There are various regulatory mechanisms which control pH, ionic balance, osmotic balance etc. in order for the body to maintain this internal environment.
  • There are a large no. of products, under the general heading replacement therapy which can be used by the physician, when the body is itself unable to correct electrolyte imbalance due to change in composition of its fluids.
  • These products includes electrolytes, blood products, acids and bases, carbohydrates, amino acids and proteins.

The three compartments in the body are:-

  • Intracellular fluid which accounts for 60-65% of body weight.
  • Interstitial fluid /tissue fluid which is a solution that surrounds the cell. It is responsible for 12-15% of body weight.
  • Plasma/vascular fluid (blood) which accounts for 4-5 % of body weight.

The term extracellular fluid [ECF] includes both interstitial and vascular fluid. Each fluid compartment has a distinct solute pattern. The solution in each compartment is ionically balanced. For example- NaCl, HCO3- are found in ECF while potassium, magnesium, PO43-, SO42- are found in ICF.


  1. Chloride (Cl) : ECF ion
    Responsible for maintaining proper hydration, osmotic pressure and normal anion – cation balance in ECF compartment.
    Food is the main source of chloride.
  2. Phosphate (PO₄³⁻) : Principle anion of ICF
    It is essential for proper Ca+2 Metabolism for normal bones and teeth development.
    It is a part of an important buffer system of body.
    It is the means of storing energy as ATP.
  3. Bicarbonate (HCO3) : It is present in ECF
    Along with Carbonic acid , it functions as buffer system of body. Its deficiency causes metabolic acidosis and leads to metabolic alkalosis.
  4. Sodium (Na+) : ECF
    It is responsible for maintaining normal hydration and osmotic pressure.
    Conditions causing low Na+ levels are:
    Extreme urine loss
    Metabolic acidosis
    Kidney damage
  5. Potassium (K+) : ICF
    It plays role during transmission of nerve impulses.
    Both excess and deficiency can be serious to the patient.
  6. Calcium (Ca+2) : ECF
    99% of body Ca is in bones. The remaining Ca is found in extracellular fluid components. functionally 99% of body Ca is supportive.
    The remaining ionic Ca is involved in neuro-hormonal functions blood clotting, muscles contraction and other biochemical process.
  7. Magnesium (Mg+2) : ICF
    50% of total body Mg+2 is combined with Ca+2 and Phosphates in bones . It is involved in many enzyme actions involving phosphate metabolism
    It is also important for protein synthesis and smooth functioning of neuromuscular system. ELECTROLYTES USED IN REPLACEMENT THEORY :
    Na replacement – NaCl
    K replacement – KCl
    Ca replacement – CaCl2
    Ca (gluconate)
    Mg replacement – MgSO4
    It contains 99% – 105% NaCl.
    In order to be isotonic , a salt solution should be 0.9% w/v.
    Preparation: Present in seawater in shallow panes ; for removing impurities like Na2SO4 ,MgCl2 , MgSO4 & CaCl2 .NaCl is dissolved in water and treated with lime and alum.

Properties : It occurs as colorless crystal or white crystalline powder and odorless
Highly soluble in water, little less soluble in glycerin.
Slightly soluble in alcohol.
Solutions may be sterilized by autoclaving or by filtration.
It gives the reactions of sodium and of Chlorine.
Assay : Modified Volhard’s method.
Titrate with standard solution of ammonium thiocyanate ferric alum/ferric ammonium sulphate.
End point – Appearance of permanent brick red color.
An acidified solution of sodium chloride (with HNO3) is treated with known excess ant of standard silver nitrate solution. The presence of nitrobenzene or dibutyl Phthalate silver nitrate will react quantitatively with NaCl.
The remaining unreacted AgNO3 is determined by Titration c standard solution of ammonium thiocyanate with ferric alum as an indicator.
Nitrobenzene or Dibutyl Phthalate is added to formulate the ppt. of AgCl otherwise filtration is required.

Each ml of 0.17 AgNO3 ≡ 0.005844g of NaCl.

NaCl +AgNO3 ⟶ NaNO3 + AgCl↓
AgNO3 +Nh4SCN ⟶ AgSCN + NH4NO3
NH4SCN + Fe+3 ⟶ Fe(SCN) Ferric thiocyanate (brick red)
Uses :
Used as an electrolyte replenisher.
Used in dehydration and sodium deficiency
Also used as an emetics.

POTASSIUM CHLORIDE : Potassium replacement theory
Preparation : It may be prepared by the action of HCl on K2CO3 or KHCO3
K2CO3 + HCl ⟶ KCl + CO2↑ +H2O
Properties : It occurs as colorless, crystal or white crystalline powder odorless, saline taste , soluble in water, less soluble in glycerol/glycerin, insoluble in alcohol.
Solution is neutral to litmus.
The solution in water gives the reaction of K+ and Cl
Uses :
1. Electrolyte replenisher
2. Used in potassium deficiency.

Official KCl preparation :

  • Effervescent KCl tablets
  • KCl mixture
  • injection
  • oral solution
  • KCl in dextrose injection.
  • KCl , KHCO3 , K+ citrate effervescent tablets
  • KCl glucose intravenous infusion (IV)
  • KCl ,NaCl, Glucose IV.
  • KCl , NaCl IV

CALCIUM GLUCONATE : [ C12H22CaO14·H2O] Calcium salt of gluconic acid.

solubility increases on heating. It is insoluble in alcohol. (PH = 6 to 7). Occurs white crystalline powder/ granules tasteless, odorless, soluble in water.
Preparation : It is prepared by reacting gluconic acid without CaCO3.

Assay : Principle : Complexometric titration
Titration: Standard solution of disodium edetate [EDTA]
Indicator: Mordant black II

NOTE : 1. Strong ammonia solution as buffer is used.
2. Known volume of standard Magnesium sulphate is added.


The assay is based on CT. A known volume of MgSO4 is added to make the end point sharp.
MgSO4 also forms a similar complex without EDTA . This Titration is carried but in the presence of buffer. End point is change of color from red to blue. METHOD :

  • An accurately weighted amount of sample is dissolved in warm water on cooling.
  • known volume of standard MgSO4 solution is added.
  • Strong NH3 solution is also added.
  • Mixture is titrated with standard solution of disodium edetate using Mordant black II as indicator from the volume of standard EDTA required.
  • subtract the volume of the magnesium sulphate solution added.

EQUIVALENT FACTOR: 1 ml of the remainder of 0.05M EDTA is ≋ 0.02242g of Ca gluconate

USES: It is used as Ca replenished/treat its deficiency.


Thermal administration of fluid that contains a suitable combination of carbohydrates and electrolytes is known as oral rehydration therapy (ORT)
This combination is dispensed in water and solution obtained and the combination is called oral rehydration salt.
ORS (WHO) contains:

  • NaCl⟶3.5g
  • KCl ⟶1.5g
  • Sodium glucose ⟶ 20g
  • For solution in 1 L of water.
  • In acute diarrhea loss of water and electrolytes can lead to significant dehydration and metabolic imbalance which can lead to fatal results specially in infants.
  • If a solution containing suitable concentration of glucose and NaCl is administered orally. Absorption of both Na+ and water is greatly increased due to the action of glucose as a carrier Molecule in the transport of sodium together with water from the intestine. Starches and sucrose also have similar effect as they release glucose in the intestine.
  • There are following 2 basic treatment phases with O.R.T. :
  • Rehydration phase –
  • It involves replacement of fluid and electrolytes lost to Diarrhoea and vomiting.
  • Maintenance phase –
  • It involves replacement of losses due to diarrhea, vomiting and
  • Ophthalmic Loss due to respiration sweating and urination which are especially high in infants.

Each packet of 35g contains :

  • NaCl (1.25g)
  • KCl (1.5g)
  • Sodium citrate (2.9g)
  • Anhydrous Dextrose (27.0g)
  • Other excipients which are dissolved in 1L water and supplies electrolytes as:
  • Na+ ( 5 meq/L)
  • K+ (20 meq/L)
  • Citrate (30 meq/L)
  • Cl- (4 meq/L)
  • Dextrose (150 mmol/ L)
  • This ORS is used in case of diarrhea, vomiting , muscles weakness.
  • Also used by athletes and industrial workers to replace fluid losses.
  • The powder is stored in dry place away from moisture.

Physiological Acid–Base balance:

  • Body uses different means to maintain Physiological balance. Acids are constantly being produced during metabolism. Eg:- H2CO3 from CO2 and lactic acid from anaerobic metabolism.
  • Since most metabolic reactions take place only within a very narrow PH range i.e. 7.38-7.42, the body utilizes several efficient buffer system. Eg:- Bicarbonate – Carbonic acid buffer system which is found in plasma and kidneys and the Di/Monohydration phosphate buffer system found in the cell and kidney
  • In RBC hemoglobin is present which is the most effective single buffer system for buffering the H2CO3 produced during metabolic process.
  • Mechanism by which PH is maintained:
  • Respiratory control:- Affects the management of blood PH when respiratory center is stimulated , it alters the rate of respiration. It affects the rate of removal of Carbon dioxide from body fluid which leads to change in PH of blood by the formation of (HCO3)and (CO3)-2.
  • Renal mechanism:-
  • Absorption of certain ions and removal of others by the kidney controls the Ph of blood .Due to a variety of reasons the body acids level may increase and alkali level decrease.
  • (Below normal producing acidosis) or the acid level; may decrease and or alkali level increase above normal, producing alkalosis.
  • The term acidosis and alkalosis refers to the PH dropping slightly below 7.38 or increasing slightly above 7.42 respectively.
  • If the body can restore the PH back to 7.35 -7.45 by alteration in respiration and kidney function , it is referred to as compensated metabolic acidosis or alkalosis
  • If after the body takes corrective actions and the buffer values are not filled back to their normal ranges it is known as uncompensated acidosis or alkalosis.

Following are the principle disorders of acid-base balance:-

  • Respiratory acidosis : Due to potentiation of CO2 in body.
  • Respiratory alkalosis : Due to excessive loss of CO2
  • Metabolic acidosis : Due to failure to excrete acid by kidneys or due to formation of excessive acidic metabolites or due to conditions like diarrhea and vomiting.
  • Metabolic alkalosis : when the PH is above the defined (normal) PH range ( PH shift towards alkaline side)
  • Electrolyte used to treat metabolic acidosis :
  • Sodium acetate
  • Potassium acetate
  • NaHCO3
  • KHCO3
  • Sodium citrate
  • Potassium citrate
  • Sodium lactate
  • Electrolyte treats metabolic alkalosis:
  • Ammonium chloride.