Hyponatremia

Hyponatremia

 Hyponatremia is clinically defined as serum sodium < 135 mmol/L.

 Hyponatremia is the most common electrolyte abnormality.

 Symptoms of hyponatremia include nausea, vomiting, , muscle

weakness/cramps, headache, encephalopathy, and coma.

 Risk factors include advanced age, intensive athletic activity, and drugs

including thiazide diuretics, antidepressants, opioids, NSAIDs and Ecstacy.

 Treatment of asymptomatic patients consists of correction of the underlying

disorder, whereas IV saline should be used to correct symptomatic patients.

Hypovolemic Hyponatremia (thirst, dry mucus membranes, dry mouth) due to

total body sodium loss, with relatively smaller loss in body water.

 If Urine Sodium > 20 mEq/L, renal solute loss may be cause.

o Increased diuresis, leading to increased ADH secretion

-loop diuretics (bumetanide, furosemide, torsemide, etc.)

-osmotic diuretics (mannitol, isosorbide, etc.)

-glucosuria (DM1, DM2): treat underlying DM.

o Post-obstructive diuresis (POD) (sudden release of bladder

obstruction, with decrease in hydrostatic bladder pressure, causes

sudden increase in diuresis)

 Urine Sodium ≤ 20 meq/L indicates extrarenal solute loss from different

causes of dehydration. Common etiologies include:

o GI loss

o Hyperhidrosis (eg Exercise Associated Hyponatremia (EAH))

o Diarrhea

o Vomiting

Hypervolemic Hyponatremia (peripheral edema, ascites, SOB)

 Urine Sodium > 20 mEq/L

 Urine Sodium ≤ 20 meq/L Extrarenal solute loss

o Renal Failure

-Pre- renal (poor renal perfusion, HF, cirrhosis)

-Intrinsic

-Post- renal (obstruction)

o Post-obstruction (sudden release of bladder obstruction)

o Edematous Disorders

-HF

-Cirrhosis

-Nephrotic Syndrome

Euvolemic Hyponatremia (no edema, but with volume expansion in the body with

hyponatremia)

 Urine Sodium is usually > 20 mEq/L

o Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

-Causes: Pneumonia, Tumor, Guillaine Barre Syndrome, Encephalitis,

Head Trauma

o Endocrinopathies

-Glucocorticoid deficiency: Addison’s disease, congenital adrenal

hyperplasia, secondary, or tertiary adrenal insufficiency

-Hypothyroidism: decreased kidney function

o Potassium Depletion, can lead to dysfunction of potassium-sodium

pump in collecting duct and loss of sodium.

o Overhydration from polydipsia: although ADH is appropriately

suppressed in these patients, excessive drinking of water overwhelms

kidneys’ ability to excrete.

Also: Pseudohyponatremia or Isotonic Hyponatremia (laboratory artifact from

blood abnormalities, serum tonicity will be 280 – 295 mOsm/L)

-Hyperlipidemia (HLD)

-Hyperproteinemia (after strenuous exercise, in MM, etc)