160. Syndrome of impaired diuresis - etiology, pathogenesis, clinical manifestations.

Syndrome of Impaired Diuresis

(Also known as Oliguria Syndromes / Water Retention Disorders)

✅ Definition

Syndrome of impaired diuresis refers to a failure to adequately excrete water via urine, leading to fluid retention, dilutional hyponatremia, and possible volume overload. It occurs due to renal or hormonal dysregulation of water balance.

✅ Etiology

✅ Pathogenesis

1. 1 Reduced free water excretion due to either:

• Inappropriate ADH secretion (e.g., SIADH), or
• Impaired renal ability to dilute urine (e.g., CKD).

2. Water retention → dilutional hyponatremia (low plasma sodium).
3. Expansion of extracellular fluid volume → possible edema, pulmonary congestion, or hypertension.
4. Low serum osmolality with inappropriately concentrated urine (in SIADH especially).
5. In renal causes, impaired tubular response or nephron loss reduces the capacity to concentrate or dilute urine properly.

✅ Clinical Manifestations

✅ Notes:

• In SIADH, ADH is secreted despite normal or low plasma osmolality → euvolemic hyponatremia.
• In CHF or cirrhosis, there is perceived hypovolemia due to low effective circulating volume → compensatory ADH secretion → water retention.

✅ Summary Table

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