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).

• Nocturnal polyuria (NP), characterized by overproduction of urine at night (more than 20%-33% of total 24-hour urine volume depending on age). It can be caused by intake, urological, nephrological, hormonal, sleep, and cardiovascular factors.

Causes

Common causes

• The most common causes of polyuria are:
  • Psychogenic polydipsia
  • Diabetes insipidus DI (central and nephrogenic)
  • Chronic kidney disease (CKD)
  • Uncontrolled diabetes mellitus (DM)

• Nocturnal Polyuria (NP) can be caused by different medical conditions including:
  • Congestive heart failure (CHF)
  • Diabetes mellitus (DM)
  • Obstructive sleep apnea (OSA)
  • Peripheral edema
  • Excessive nighttime fluid intake
  • Abnormalities in antidiuretic hormone arginine vasopressin (AVP) secretion can cause overproduction of urine at night
  • Nocturnal Polyuria Syndrome, in the absence of any medical condition, it can be due to impaired circadian release of Arginine vasopressin(AVP).

Diagnosis

• Water deprivation test combined with desmopressin administration is the diagnostic gold standard, it differentiates between the causes of the polyuria‐polydipsia syndrome.

• The c‐terminal portion of the larger precursor peptide of Arginine Vasopressin AVP (co-peptin), has been evaluated in the setting of polyuria‐polydipsia syndrome, can be useful for the differential diagnosis.

Management

Diagnostic Approach

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