Water, sodium and potassium

Overview Introduction Distribution of body fluids Electrolytes Major electrolyte imbalances

Introduction To be in balance, the quantities of fluids and electrolytes leaving the body should be equal to the amounts taken in. Electrolytes are molecules that release ions in water. Anything that alters the concentrations of electrolytes will also alter the concentration of water, and vice versa.

Distribution of body fluids Fluids occur in compartments (intracellular and extracellular compartments) in the body, and the movement of water and electrolytes between these compartments is regulated. Fluid Compartments The average adult female is 52% water by weight, while a male is 63% water, the difference due to the female's additional adipose tissue.

Electrolytes Na+: most abundant electrolyte in the body. K+ : essential for normal nerve impulse. Cl-: Regulates osmotic pressure and assists in regulating acid base balance. Ca2+: usually combined with phosphorus to form the mineral salts of bone and teeth, promotes nerve impulses, muscle contraction/relaxation.

Electrolytes Mg +: Plays a role in carbohydrate and protein metabolism, storage and use of intracellular energy and neural transmission. Important in the functioning of the heart, nerves and muscle.

Electrolyte distribution

MAJOR ELECTROLYTE IMBALANCES Hyponatremia (sodium deficit < 130mEq/L) Hypernatremia (sodium excess >145mEq/L) Hypokalemia (potassium deficit <3.5mEq/L) Hyperkalemia (potassium excess >5.1mEq/L)

SODIUM/CHLORIDE IMBALANCES Regulated by the kidneys Influenced by the hormone aldosterone Na is responsible for water retention and serum osmolality level Chloride ion frequently appears with the sodium ion Normal Na = 135-145 mEq/L Chloride 95-108 mEq/L Na and CL are concentrated in ECF

Osmolality Is the osmotic pressure of blood. It measures the amount of solute concentration per unit of total volume of a particular solution. The normal values in serum are 280 to 295 mOsm/L.

Serum osmolality may be increased with: Dehydration Diabetes Hyperglycemia Hypernatremia Ingestion of ethanol, methanol, or ethylene glycol Kidney damage Mannitol therapy Shock

Serum osmolality may be decreased with: excess hydration Hypernatremia Inappropriate ADH Secretion

Hyponatremia Excessive sodium loss or H2O gain A normal sodium level is between 135 and 145 (mEq/L). Hyponatremia occurs when the sodium in your blood falls below 135 mEq/L.

Causes of Hyponatremia Prolonged diuretic therapy Excessive diaphoresis Insufficient Na intake GI losses – suctioning, laxatives, vomiting Administration of hypotonic fluids Compulsive water drinking Labor induction with oxytocin Cystic fibrosis alcoholism

Clinical manifestations Headache Faintness Confusion Muscle cramping/twitching Increased weight Convulsions

Types of hyponatremia 
The imbalance between sodium and water in your blood may occur in three primary ways: In hypervolemic hyponatremia, your body has too much water and sodium but the water gain is greater. Hypervolemic hyponatremia is commonly the result of kidney failure, heart failure or liver failure. In euvolemic hyponatremia, your water level is too high. This condition is commonly due to chronic health conditions, cancer or certain medications. In hypovolemic hyponatremia, you have too little water and sodium but the sodium loss is greater. This may occur, for example, when exercising in the heat without replenishing your fluid electrolytes or with marked blood loss.

Test yourself Osmolality 260 mmol/L (280 -296 mmol/L) A 63-year-old man had a persistent chest infection, for the previous 2 months. There were no signs of dehydration or oedema. Examination of blood yielded the following results: What is the most likely cause of low sodium and osmolality? Na+ 118 mmol/L (135- 145mmol/L) Osmolality 260 mmol/L (280 -296 mmol/L) Urine Na+ 74 mmol/L Urine osmolality 625 mmol/kg

Test yourself _____is the most common extracellular cation, while _____ is the most abundant intracellular cation. Sodium; Ca++ K+; Na+ Sodium; potassium K+; Ca++

Test yourself When serum sodium is low , it means Total body sodium is low Total body sodium is high Total body sodium is normal Any of the above

Test yourself The imbalance known as ____________ can be caused by certain diuretic medications. Hyponatremia Hyperatremia Hypokalemia hyperkalemia

Test yourself Serum sodium is 130 with serum osmolality of 300 mOsm/kg. Most likely it is inappropriate ADH secretion Diabetic ketoacidosis Uremia Ethanol intoxication

Hypernatremia Occurs with excess loss of H2O or excessive retention of Na Can lead to death if not treated

Causes of Hypernatremia Vomiting/diarrhea Diaphoresis Inadequate ADH Some drugs Hypertonic fluids/tube feedings Major burns

Types of Hypernatremia

Hypokalemia Hypokalemia is defined as potassium level less than 3.5 mEq/L Moderate hypokalemia is a serum level of 2.5 - 3 mEq/L. Severe hypokalemia is defined as a level less than 2.5 mEq/L.

What causes hypokalemia? GI losses (vomiting and diarrhea) Renal losses Drugs (diuretics and corticosteroids) Alkalosis

Hyperkalemia Is the commonest and most serious electrolyte emergency encountered in clinical practice.

Causes Renal failure Mineralocorticoid deficiency Acidosis Potassium release from damaged cells

Match column A with the correct answer from B Cl- Most abundant negative electrolyte in intracellular fluid Na+ Most abundant positive electrolyte in intracellular fluid K+ Least abundant positive electrolyte in extracellular fluid Mg++ Most abundant positive electrolyte in extracellular fluid HPO4-- Most abundant negative electrolyte in extracellular fluid

Hyperkalemia is defined as a) reduction of plasma calcium level. b) increase in plasma potassium level. c) increase in plasma sodium level. d) decrease in plasma potassium level

Test Yourself A 55 year old man, was trapped for 7 hours in railway accident. He sustained severe multiple injuries. The following biochemical results were obtained on admission: Na+ = 141 mmo/l K+ = 8.1 mmo/l What is the diagnosis?

References Marshall, W. and Bangert, S. (2008). Clinical chemistry (6th ed.). Edinburgh, London: Mosby Elsevier. ISBN 0723434557 (chapter 2) Gaw, A. et al. (2004). Clinical Biochemistry (3rd ed.) Beckett, G. et al. (2008). Clinical Biochemistry (8th ed.) Bishop., et al. (2000). Clinical Chemistry (4th ed.) http://www.japi.org/december_2008/R-1.html