Paradoxically, increased urine output (polyuria) can cause dehydration and electrolyte disturbances, rather than just result from them.
Pathophysiology
- Osmotic diuresis: Glucose (uncontrolled diabetes), mannitol, urea (high protein/tube feeds) → water follows solute.
- Water diuresis: Diabetes insipidus (central/nephrogenic), psychogenic polydipsia, post‑obstructive diuresis.
- Pharmacologic: Diuretics (loop, thiazide, osmotic), SGLT2 inhibitors, lithium.
Consequences
- Dehydration: Thirst, dry mucous membranes, orthostatic hypotension, tachycardia, reduced skin turgor.
- Electrolyte losses: Na⁺ (hyponatremia or hypernatremia depending on replacement), K⁺ (hypokalemia → arrhythmias, weakness), Mg²⁺, Ca²⁺, phosphate.
- Renal impairment: Pre‑renal AKI from volume depletion.
Evaluation
- 24‑hr urine volume, osmolality, electrolytes.
- Serum osmolality, glucose, calcium, TSH.
- Water deprivation test (for DI).
Management
Treat underlying cause; replace fluid/electrolyte losses guided by labs and clinical status. Monitor for overcorrection (especially in hypernatremia).
