Electrolyte Imbalances In The Body Notes

Dehydration

Dehydration is a state of pure deprivation of water leading to sodium retention and hence a state of hypernatraemia. In other words, there is only loss of water without loss of sodium. Clinically, the patients present with intense thirst, mental confusion, fever, and oliguria.

Read And Learn More: General Pathology Notes

Etiology:

Pure water deficiency is less common than salt depletion but can occur in the following conditions:

• GI excretion:
  • Severe vomiting
  • Diarrhoea
  • Cholera
•  Renal excretion:
  • Acute renal failure in diuretic phase
  • Extensive use of diuretics
  • Endocrine diseases for example, Diabetes insipidus, Addison’s disease
•  Loss of blood and plasma:
  • Severe injuries, severe burns
  • During childbirth
• Loss through skin:
  • Excessive perspiration
  • Hyperthermia
• Accumulation in body cavities:
  • Sudden development of ascites
  • Acute intestinal obstruction with accumulation of fluid in the bowel.

Morphologic Features:

There are no particular pathological changes in organs, except in advanced cases when the organs are dark and shrunken. However, there are haematological and biochemical changes.

There is haemoconcentration as seen by increased PCV and raised haemoglobin. In the late stage, there is rise in blood urea and serum sodium. Renal shutdown and a state of shock may develop.

Overhydration

Overhydration is increased extracellular fluid volume due to pure water excess or water intoxication. Clinically, the patients present with disordered cerebral function for example, Nausea, Vomiting, Headache, Confusion and in severe cases convulsions, coma, and even death.

Etiology:

Overhydration is generally an induced condition and is encountered in the following situations:

• Excessive unmonitored intravascular infusion:
  • Normal saline (0.9% sodium chloride)
  • Ringer lactate
• Renal retention of sodium and water:
  • Congestive heart failure
  • Acute glomerulonephritis
  • Cirrhosis
  • Cushing’s syndrome
  • Chronic renal failure

Morphologic Features:

Sudden weight gain is a significant parameter of excess of fluid accumulation. Haematological and biochemical changes include the following:

• Reduced PCV.
• Reduced plasma electrolytes and lowered plasma proteins.

Derangements of Body Water:

Oedema is abnormal and excessive accumulation of free fluid in the interstitial tissue spaces and serous cavities.

Oedema may be localised when limited to an organ or limb, and generalised (anasarca or dropsy) when it is systemic in distribution, particularly noticeable in the subcutaneous tissues.

Depending upon fluid composition, oedema fluid may be transudate which is more often the case, such as in oedema of cardiac and renal disease, or exudate such as in inflammatory oedema.

Various mechanisms, operating singly or in combination, which produce oedema are:

• Decreased plasma oncotic pressure, increased capillary hydrostatic pressure, lymphatic obstruction, tissue factors (increased oncotic pressure of interstitial fluid, and decreased.
• Tissue tension), increased capillary permeability, and sodium and water retention.
• Generalised oedema of renal origin occurs in nephrotic syndrome, nephritic syndrome, and in renal failure due to acute tubular injury.
• Cardiac oedema is generalised and dependent type and develops in right-sided and congestive cardiac failure.
• Acute pulmonary oedema results from either the elevation of pulmonary hydrostatic pressure or from increased capillary permeability from various causes.
• In cerebral oedema, fluid-electrolyte exchange occurs at the blood-brain barrier because there are no lymphatics. Cerebral oedema can be vasogenic, cytotoxic and interstitial.
• Dehydration is pure deprivation of water leading to sodium retention and a state of hypernatraemia.
• Overhydration is increased extracellular fluid volume due to pure water excess or water intoxication.

Disturbances Of Electrolytes And PH Of Blood

Electrolyte Imbalance:

It may be recalled here that normally the concentration of electrolytes within the cell and in the plasma is different. Intracellular compartment has higher concentration of potassium, magnesium and phosphate ions than the blood, while extracellular fluid (including serum) has higher concentration of sodium, chloride, calcium and bicarbonate ions.

In health, for electrolyte homeostasis, the concentration of electrolytes in both these compartments should be within normal limits.

Normal serum levels of electrolytes are maintained in the body by a careful balance of 4 processes: Their

1. Intake
2. Absorption
3. Distribution and
4. Excretion.

Disturbance in any of these processes in diverse pathophysiologic states may cause electrolyte imbalance.

Among the important components in electrolyte imbalance, abnormalities in serum levels of sodium (hypo- and hypernatraemia), potassium (hypo- and hyperkalaemia), calcium (hypo- and hypercalcaemia) and magnesium (hypo- and hypermagnesaemia) are clinically more important.

A list of important clinical conditions producing abnormalities in sodium and potassium. While it is beyond the scope of this book to delve into the subject of electrolyte imbalances in detail.

A few general principles are as under:

• Electrolyte imbalance in a given case may result from one or more conditions.
• Resultant abnormal serum level of more than one electrolyte may be linked to each other for example, In abnormality in serum levels of sodium and potassium; calcium and phosphate.
• Generally, the reflection of biochemical serum electrolyte levels is in the form of metabolic syndrome and clinical features rather than morphological findings in organs.
• Clinical manifestations of a particular electrolyte imbalance are related to its pathophysiologic role in that organ or tissue.

pH OF BLOOD:

During metabolism of cells, carbon dioxide and metabolic acids are produced. CO combines with water to form carbonic acid. The role of the bicarbonate buffering system in the extracellular compartment has already been stated above.

In order to have acid-base homeostasis to maintain blood pH of 7.4, both carbonic acid and metabolic acids must be excreted from the body via lungs (for CO₂) and kidneys (for metabolic acids).

Thus, the pH of blood depends upon 2 principal factors: serum concentration of bicarbonate; and partial pressure of CO₂ that determines the concentration of carbonic acid.

The disorders of the pH of the blood are due to acid-base imbalance—it is termed as acidosis when blood pH is below 7.4 and alkalosis when blood pH is above 7.4.

Acidosis and alkalosis may be due to metabolic causes or due to ventilator function of the lungs:

• Alterations in the blood bicarbonate levels are metabolic acidosis and alkalosis.
• Alterations in Pco₂ (which depends upon the ventilatory function of the lungs) are respiratory acidosis and alkalosis.
• Abnormalities in acid-base homeostasis produce diverse clinical manifestations due to pathophysiologic derangements as under:

Metabolic Acidosis:

A fall in the blood pH due to metabolic component is brought about by fall of bicarbonate level and excess of H+ ions in the blood. This occurs in the following situations:

• Production of large amounts of lactic acid (lactic acidosis) for example, In vigorous exercise, shock.
• Uncontrolled diabetes mellitus (diabetic ketoacidosis).
• Starvation.
• Chronic renal failure.
• Therapeutic administration of ammonium chloride or acetazolamide (Diamox).

Electrolyte imbalances of sodium and potassium:

High blood levels of H⁺ ions in metabolic acidosis stimulate the respiratory centre so that the breathing is deep and rapid (air hunger or Kussmaul’s respiration). There is fall in the plasma bicarbonate levels.

Metabolic Alkalosis:

A rise in the blood pH due to rise in the bicarbonate levels of plasma and loss of H⁺ ions is called metabolic alkalosis.

This is seen in the following conditions:

• Severe and prolonged vomitings. Administration of alkaline salts like sodium bicarbonate.
• Hypokalaemia such as in Cushing’s syndrome, increased secretion of aldosterone.

Clinically, metabolic alkalosis is characterised by depression of respiration, depressed renal function with uraemia and increased bicarbonate excretion in the urine. The blood level of bicarbonate is elevated.

Respiratory Acidosis:

A fall in the blood pH occurring due to raised Pco₂ consequent to hypoventilation of lungs (CO₂ retention) causes respiratory acidosis.

This can occur in the following circumstances:

• Air obstruction as occurs in chronic bronchitis, emphysema, asthma.
• Restricted thoracic movement for example, In pleural effusion, ascites, pregnancy, kyphoscoliosis.
• Impaired neuromuscular function for example in, Poliomyelitis, Polyneuritis.

Clinically, there is peripheral vasodilatation and raised intracranial pressure.

If there is severe CO₂ retention, patients may develop confusion, drowsiness and coma. The arterial Pco2 level is raised.

Respiratory Alkalosis:

A rise in the blood pH occurring due to lowered Pco2 consequent to hyperventilation of the lungs (excess removal of CO₂) is called respiratory alkalosis.

This occurs in the following conditions:

• Hysterical overbreathing.
• Working at high temperatures.
• At high altitude.
• Meningitis, encephalitis.
• Salicylate intoxication.

Clinically, the patients with respiratory alkalosis are characterised by peripheral vasoconstriction and consequent pallor, lightheadedness and tetany. The arterial Pco₂ is lowered.

Disturbances of Electrolytes and pH of Blood:

Normal serum levels of electrolytes are maintained in the body by a careful balance of 4 processes: their intake, absorption, distribution and excretion. The pH of blood depends upon serum concentration of bicarbonate and partial pressure of CO₂.

Metabolic acidosis is a fall in the blood pH (below 7.4) due to fall of bicarbonate level and excess of H⁺ ions in the blood, while a rise in the blood pH (above 7.4) due to rise in bicarbonate levels of plasma and loss of H⁺ ions is called metabolic alkalosis.

Raised Pco ₂consequent to hypoventilation of lungs (CO₂ retention) causes respiratory acidosis, while a lowered Pco₂ consequent to hyperventilation of the lungs (excess removal of CO₂) is called respiratory alkalosis.