Symptomatic hyponatremia

Specialty: Endocrine and metabolic.

• water poisoning of endocrine origin
• symptomatic low plasma sodium
• symptomatic hypoosmolarity

Why it occurs

• Syndrome of Inappropriate Secretion of Antidiuretic Hormone or SIADH (autonomous and persistent release of vasopressin mediated by small cell lung tumors, disorders of the central nervous system, drugs or idiopathically)
• Primary or secondary adrenal insufficiency (cortisol deficiency suspends tonic inhibition of vasopressin secretion in the hypothalamus, increasing free water reabsorption)
• Severe hypothyroidism or myxedema coma (reduced cardiac output with decreased renal perfusion triggering non-osmotic release of ADH)
• Primary polydipsia (massive and compulsive intake of water that exceeds the maximum dilution capacity of the renal tubules, usually >12 liters per day)
• Use of thiazide diuretics (inhibition of the Na-Cl cotransporter in the distal convoluted tubule that promotes natriuresis with selective water retention mediated by ADH)

Initial workup

Immediate measurement of serum sodium and measured plasma osmolarity (to rule out pseudohyponatremia due to hypertriglyceridemia or severe hyperproteinemia); urinary osmolarity (values ​​>100 mOsm/kg suggest SIADH or adrenal insufficiency); urinary sodium concentration in isolated sample (>40 mEq/L is characteristic of SIADH in the presence of normal salt intake); basal plasma cortisol at 8:00 AM; TSH and free T4; and CT scan of the chest and brain to rule out underlying causes of SIADH.

Standard management

• 3% hypertonic saline solution — intravenous infusion calculated strictly according to the body sodium deficit in neurological emergency situations, with the objective of raising plasma sodium from 4 to 6 mEq/L in the first hours, limiting the correction to less than 8-10 mEq/L in 24 hours
• Hopperptan — selective antagonist of the V2 vasopressin receptor orally, indicated in euvolemic hyponatremia secondary to SIADH refractory to water restriction
• Sodium chloride in 1 gram tablets — administered orally along with strict water restriction in the long-term management of chronic SIADH
• Fludrocortisone — in case of hyponatremia due to salt loss of cerebral origin or primary adrenal insufficiency