Disorders of Sodium and water metabolism

Dr. Yahya Ibn Ilias

Alterations in Sodium Concentration

The normal serum sodium ranges from 135 to 145 mEq/L (135 to 145 mmol/L).

Serum sodium values, expressed in mEq/L, reflect the conc

entration or dilution of sodium by water, rather than its absolute value.

Because sodium and its attendant anions account for 90% to 95% of the osmolality of the ECF (normal range, 275 to 295 mOsm/kg).

Changes in serum sodium generally are accompanied by changes in serum osmolality.

Usually, water and sodium disorders are divided into three categories, based on the change of serum Na+ concentration :

Hyponatremia

Hypernatremia

Water disorder with a normal Na+ level

Hyponatremia

Hyponatremia represents a serum sodium concentration below 135 mEq/L (135 mmol/L).

Is considered severe when the serum level is below 125 mEq/L.

Hyponatremia

Hypovolumic Hyponatremia

Hyponatremia with lower volume of ECF.

As a result serum Na conc. and plasma osmotic pressure decreased.

Etiology and pathogenesis

Decrease serum Na concentration can result either by Renal or Extrarenal pathways.

Na+ loss by renal pathway :

1. Chronic use of diuretics.

2. Adrenocortical insufficiency

3. Renal tubulointerstitial disease.

4. Renal tubular acidosis.

Extrarenal pathway

1. GI tract : Excessive fluid loss e.g. severe diarrohea or vomiting.

2. Accumulation of body fluid in third space.

Alteration of metabolism and function

Hypovolumic Hyponatremia characterized with a ECF, results in Shock, BP , circulatory failure.

Na conc. in ECF causes shifting of water to ICF resulting in cellular swelling.

Kidney induced Na loss will cause a high concentration of urinary Na, while extrarenal Na loss results in lower level of Urinary Na.

In Hypovolumic Hyponatremia ECF is lowered……

What about Thirst Sensation ??

Treatment

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Hypervolumic Hyponatremia

Hypervolemic hyponatremia occurs when extracellular Na is normal or even slightly elevated, but ECF is greatly elevated.

Often represents sign of clinical hypervolemia, such as pitting edema or ascites.

Serum Na conc. , Plasma osmotic pressure.

Etiology and pathogenesis

Excessive water gain

Decrease water loss:- Most commonly induced by ARF. Besides CHF, Hepatic cirrhosis , and excessive ADH secretion.

Alteration of metabolism and function

ECF , blood ….. ??

ECF osmolality may result cellular swelling.

Swelling of brain cell may cause headache, nausea, vomiting, mental confusion etc.

Treatment

???

Hypervolemic hyponatremia

Dilutional Hyponatremia

ECF osmolality, cellular swelling

In brain, may cause of death

Water intoxication

Euvolemic hyponatremia

Euvolemic hyponatremia is characterized with decreased serum Na conc. and plasma osmotic pressure and an almost normal ECF volume.

It is often induced by SIADH.

SIADH

Syndrome of Inappropriate ADH release

Urinary excretion of water requires suppression of the antidiuretic hormone (ADH), which is released by the pituitary, and acts on the kidneys to conserve water.

If the ADH is not suppressed, normal water intake results in water retention and diluted ECF sodium concentration.

This is the most common cause of euvolemic hyponatremia.

Causes of SIADH

Carcinoma: Tumors are the most common condition associated with SIADH. Lung tumors (small cell type) most frequently associated with this syndrome.

Nonmalignant lung disease e.g. TB, Lung abscess, Pneumonia has also

been associated with SIADH.

Medication use. Antipsychotic drugs, antidepressants, anticonvulsants, narcotics, and angiotensin-converting enzyme inhibitors are among the various classes of drugs that can cause SIADH by causing inappropriate release of vasopressin.

CNS disorders: Such as trauma, infection, and hydrocephalus may causes SIADH. These conditions are caused by alteration of the usual signaling pathway from the hypothalamus and brainstem, which regulate pituitary release of vasopressin.

Hypernatremia

Hypernatremia represents a serum sodium concentration avobe 145 mEq/L (145 mmol/L).

An increase in serum sodium concentration is almost always a reflection of water loss rather than sodium gain.

Hypovolumic Hypernatremia

AKA hypertonic dehydration.

Deficit of both water and sodium, with greater loss of water.

Most common form of hypernatremia.

Hypernatremia is characterized by hypertonicity of the ECF and almost always causes cellular dehydration.

Etiology and pathogenesis

Decrease water gain

- Normally, water deficit stimulates thirst and increases water intake. Therefore, hypernatremia is more likely to occur in infants and in persons who cannot express their thirst or obtain water to drink.

Excessive water output

- Hypernatremia can also be induced by elevated blood protein or glucose level (Osmotic diuresis).

Treatment

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Hypervolumic Hypernatremia

Hypervolumic Hypernatremia means a co-existing of ECF volume increase and hypernatremia, which involve in augmented sodium and water gain, and primary sodium retention.

Etiology and pathogenesis

Too much administration of NaCO3 solution for treatment of severe metabolic acidosis or excessive addition of hypertonic solution.

Primary hyperaldesteronism or Cushing syndrome causes increase sodium and water reabsorption by kidney which in turn causes a high serum sodium conc. and expanded ECF.

Alteration of metabolism and function

Hypervolumic Hypernatremia causes hyperosmolality of ECF followed by cellular dehydration.

This may result in a dysfunction of CNS.

Treatment

???

Euvolemic hypernatremia

AKA essential hypernatremia.

Characterized with increased serum Na conc. And almost normal ECF volume.

Etiology and pathogenesis

Decreased total body water; normal or near-normal total body sodium concentration and ECF volume.

Most common when a patient does not maintain adequate water intake despite ongoing water losses, e.g insensible skin losses, respiratory losses etc.

Treatment

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Disorder of K+ metabolism

Potassium is the second most abundant cation in the body and the major cation in the ICF compartment.

Approximately 98% of body potassium is contained within body cells, with an intracellular concentration of 140 to 150 mEq/L.

The potassium content of ECF (3.5 to 5.0 mEq/L) is considerably less.

As the major intracellular cation, It is involved in a wide range of body functions, including the maintenance of the osmotic integrity of cells, acid-base balance, and the kidney’s ability to concentrate urine.

Potassium also plays a critical role in conducting nerve impulses and the excitability of skeletal, cardiac, and smooth muscle.

Hypokalemia

Hypokalemia refers to the condition in which the concentration of potassium (K+) in the blood is lower than its normal limits.

Etiology and pathogenesis

1. Abnormality of transcellular distribution :

Alkalosis : H+ moves out of the cell while Na and K move into the cell to maintain electrochemical balance during alkalosis, which may cause hypokalemia.

Others : Adrenalin, insulin increase cellular intake of K and lead to hypokalemia.

2. Inadequate intake.

3. Excessive loss by diuretics, excess mineralocorticoid.

4. Non renal K+ loss by excessive diarrhea , vomiting.

ECG changes

Most persons with a serum potassium level of less than 3.0 mEq/L demonstrate electrocardiographic (ECG) changes typical of hypokalemia.

These changes include prolongation of the PR interval, depression of the ST segment, flattening of the T wave, and appearance of a prominent U wave.

ECG findings in hypokalemia

Treatment

Hypokalemia caused by potassium deficit is treated by increasing the intake of foods high in potassium content.

Oral potassium supplements are prescribed for persons wh

ose intake of potassium is insufficient in relation to losses.

Potassium may be given intravenously when the oral route is not tolerated or when rapid replacement is needed.

Magnesium deficiency may impair potassium correction; in such cases, magnesium replacement is indicated.