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hyponatremia

Hyponatremia

Key concepts

● definition:serum[Na+]<135mEq/L.

Common etiologies:

○ SIADH: hypotonic hyponatremia (efective serum osmol<275mOsm/L) within appropriately high urinary concentration (urine osmol>100 mOsm/L) and euvolemia or hypervolemia.

○ Cerebral salt wasting (CSW): similar to SIADH but with extracellular fluid volume depletion due to renal sodium loss (urinary Na > 20 mEq/L).

● minimum W/U: serum [Na+], serum osmolality, urine osmolality, clinical assessment of volume status. If volume status is high or low: urinary [Na+] TSH (to R/O hypothyroidism).

● treatment: based on acuity, severity, symptoms & etiology; as appropriate.

● risk of overly rapid correction: osmotic demyelination (including central pontine myelinolysis).

Definition

Hyponatremia, is low sodium concentration in the blood, the most common electrolyte abnormality in clinical medicine 1).

Generally defined as a serum sodium level of less than 135 mEq/L and is considered severe when the serum sodium level is below 125 mEq/L.

Classification and Differential diagnosis

[Na+] <135 mEq/L=mild, <130=moderate, <125=severe hyponatremia.

Syndrome of inappropriate antidiuretic hormone secretion is the most common type of hyponatremia 2).

Cerebral salt wasting syndrome.

Etiology

Clinical features

Due to slow compensatory mechanisms in the brain, a gradual decline in serum sodium is better tolerated than a rapid drop. Symptoms of mild ([Na]<130 mEq/L) or gradual hyponatremia include: anorexia, headache, difficulty concentrating, irritability, dysgeusia and muscle weakness. Severe hyponatremia (<125 mEq/L) or a rapid drop (>0.5 mEq/hr) can cause neuromuscular excitability, cerebral edema, muscle twitching and cramps, nausea/vomiting, confusion, seizures, respiratory arrest and possibly permanent neurologic injury, coma or death.

1)
Thompson CJ. Hyponatraemia: new associations and new treatments. European journal of endocrinology / European Federation of Endocrine Societies. 2010;162 Suppl 1:S1-3.
2)
Ellison DH, Berl T. Clinical practice. The syndrome of inappropriate antidiuresis. N Engl J Med. 2007 May 17;356(20):2064-72. Review. PubMed PMID: 17507705.
hyponatremia.txt · Last modified: 2018/12/13 14:06 by administrador