Polyuria resident survival guide

Overview

• Polyuria is defined as urine output more than 2 L/24 hours, or 30 ml/kg/24 hours. There are 3 pathophysiologic causes of polyuria: increased thirst (idiopathic, psychogenic polydepsia, hypothalamic disease, and medications), central diabetes insipidus (DI) (decreased secretion of arginine vasopressin (AVP)), and nephrogenic diabetes insipidus (DI) (renal resistance to AVP).

Causes

Common causes

The most common causes of polyuria are: psychogenic polydipsia, diabetes insipidus (central and nephrogenic), chronic kidney disease and uncontrolled diabetes mellitus.

Approach to polyuria

Polyuria ❑ 24-hour urine volume >3L ❑ 24-hour urine volume >50 ml/kg

Urine Osmolality >300mosmol

Urine Osmolality <300mosmol

Solute diuresis ❑ Glucose ❑ Mannitol ❑ Contrast media ❑ High protein intake ❑ Diuretics ❑ Medullary cystic disease ❑ Resolving ATN ❑ Resolving obstruction

Water diuresis ❑ Primary polydipsia ❑ Diabetes inspidous

Water restriction test OR administration of hypertonic saline 0.05 mL/kg/min for 2 h

Water restriction test ❑ Overnight fluid restriction should be avoided ❑ Recommend the patient to stop drinking 2-3 hours before coming to clinic ❑ Meaure urine volume every hour ❑ Measure urine osmolality every hour ❑ Measure plasma sodium concentration every 2 hours ❑ Measure plasma osmolality every 2 hours

Test endpoints in adults: ❑ Urine osmolality reaches normal value (above 600 mosmol/kg) ❑ The urine osmolality is stable for 2 or 3 successive hourly measurements despite a rising plasma osmolality ❑ Plasma osmolality >295-300 mosmol/kg ❑ Plasma sodium is 145 or higher

Treatment

Cranial diabetes insipidus:

• Cranial DI can be managed by desmopressin orally or Intranasal (rarely used).
• Partial DI can be treated with a single nocturnal dose to prevent sleep loss due to nocturia, but complete DI requires 2-4 daily doses.

Nephrogenic diabetes insipidus:

• Withdrawal of lithium therapy usually leads to reversal of lithium-induced diabetes insipid. It can persist for years after lithium withdrawal, usually indicating that the patient has developed interstitial nephritis secondary to lithium.
• Thiazide diuretics reduce urine output by up to 50%, and indomethacin has also been used. Results are frequently unsatisfactory, treatment is directed at sufficient fluid intake to replace urinary losses.