Hyponatremia

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Hyponatremia
Hyponatremia is defined as serum sodium below 135 mmol/L
It represents excess water relative to sodium in the body
Symptoms typically appear when sodium drops below 125 mmol/L

Pathophysiology
Hyponatremia occurs due to disruption in sodium and water balance
Kidneys regulate sodium and water excretion under hormonal influence
Excess water relative to sodium leads to decreased serum sodium concentration

Causes of Hyponatremia
Increased water intake (e.g., psychiatric conditions, endurance sports)
Decreased water excretion (e.g., CHF, cirrhosis, renal failure)
Excessive sodium loss (e.g., diuretics, vomiting, diarrhea)
Hormonal imbalances (e.g., SIADH)
Certain medications (e.g., thiazide diuretics)

Clinical Presentation
Mild Hyponatremia (Na above 125 mmol/L):
Non-specific symptoms: fatigue, weakness, muscle cramps
Severe Hyponatremia (Na below 120 mmol/L):
CNS symptoms: confusion, agitation, delirium, seizures
Rate of sodium decline influences symptom severity

Diagnosis
Thorough history and physical examination
Laboratory investigations:
Serum sodium, serum osmolality
Urine sodium and osmolality
Additional tests based on suspected etiology
Stepwise approach: assess osmolality, volume status, and urine studies

Management
Consider severity of symptoms and volume status
Address underlying cause
Severe symptomatic hyponatremia: hypertonic saline (3%)
Mild-moderate asymptomatic hyponatremia: fluid restriction
SIADH: consider ADH inhibitors (e.g., demeclocycline, vaptans)

Prognosis
Depends on underlying cause, severity, and correction rate
Mild, chronic hyponatremia generally has good prognosis
Severe, acute hyponatremia can lead to significant complications
Overly rapid correction of chronic hyponatremia is may cause osmotic demyelination syndrome (central pontine demyelinosis).
Close monitoring during treatment is crucial
Some patients may require long-term management