Sodium and Water Balance

Flashcards covering the key concepts related to sodium and water balance, including regulation, measurement, disorders, and pre-analytical considerations.

Sodium and Water Regulation

The principle of sodium and water regulation.

Sodium Measurement Analytical Methods

Analytical methods for measuring sodium.

Preanalytical Errors in Sodium Measurement

Preanalytical errors associated with sodium measurement, including the electrolyte exclusion effect (pseudohyponatremia).

Hyponatremia and Hypernatremia

Hyponatremia (low sodium) and hypernatremia (high sodium).

Sodium (Na)

Major extracellular cation that maintains fluid distribution and osmotic pressure.

Renin-Angiotensin-Aldosterone System (RAAS)

System that controls sodium distribution, influenced by ACE inhibitors.

Antidiuretic Hormone (ADH)

Increases tubular permeability to water by insertion of aquaporins into the apical membrane of collecting ducts.

Most Common Method for Sodium Measurement

Ion selective electrode (ISE).

Indirect ISE Method

Dilution of the sample required; subject to pseudohyponatremia.

Direct ISE Method

No dilution of the sample; not affected by high lipid and protein concentrations.

Potentiometry

Measures changes in ion concentration.

Osmolality

Number of solute particles per kg of water.

Osmolarity

Concentration of an osmotic solution when measured in litres of the solution.

Hyponatremia Definition

Decreased plasma Na concentration (<130 – 135 mmol/L).

Hypernatremia Definition

Increased plasma Na concentration (>150 mmol/L).

Pseudohyponatremia

Falsely low measured Na in diluted sample using indirect ISE method due to increased non-aqueous components.

Electrolyte Exclusion Effect (EEE)

Exclusion of electrolytes from the fraction of total plasma volume that is occupied by non-aqueous components.

↓ Plasma Na concentration and Plasma osmolality is LOWER than the normal range

True hyponatremia.

Causes of Hyponatremia (Na Deficit)

Addison’s disease, diuretics, gastrointestinal loss, skin loss.

Causes of Hyponatremia (Water Excess)

Syndrome of inappropriate ADH secretion (SiADH), liver failure, congestive heart failure, renal failure.

Diuretics

Anti-hypertensive medications that promote Na excretion and water loss.

Causes of Hypernatremia (Na Gain)

Conn’s syndrome, Cushing’s syndrome, Sodium bicarbonate therapy, Sea water drowning.

Causes of Hypernatremia (Water Loss)

Not enough water intake, Dehydration, Water loss through diarrhoea, vomiting, bleeding or perspiration, Osmotic diuresis, Diabetes insipidus.

Diabetes Insipidus

A condition characterized by excessive thirst and frequent urination due to the body's inability to regulate fluid balance, often caused by insufficient ADH or resistance to ADH.

Syndrome of Inappropriate ADH Secretion (SIADH)

A syndrome characterized by the excessive release of antidiuretic hormone (ADH), leading to water retention and hyponatremia.

Conn’s Syndrome

A condition resulting from excessive aldosterone production by the adrenal glands, leading to sodium retention, potassium loss, and high blood pressure.

Cushing’s Syndrome

A hormonal disorder caused by prolonged exposure of the body's tissues to high levels of the hormone cortisol.

Addison’s Disease

A rare, chronic endocrine disorder in which the adrenal glands do not produce sufficient steroid hormones (cortisol and aldosterone).

Osmotic Diuresis

Increased urination due to the presence of certain substances in the small tubes of the kidneys, causing a decrease in water reabsorption back into the body.