Definition and pathophysiology

• Due to an osmotic or a woter diuresis: almost always due to osmotic diuresis in inpatients Workup

• Perform a timed urine collection (6 h sufficient) and measure Uovn

• 24-h osmole excretion rate 24-h UOP (actual or estimate) x U^

>1000 mOsm d -* osmotic diuresis • 800 mOsm d water diuresis

Osmotic diuresis

• Etiologies

Glucose (uncontrolled diabetes mellitus) Mannitol

Urea: recovering ARF. T protein feeds, hypercatabolism (burns, steroids). Gl bleed NaCI administration

• Treatment: address underlying cause, replace free-water deficit and ongoing losses Water diuresis

• Etiologies: Dl (NaM™, >140) or 1° polydipsia (Na*™ <140)

see "Hypernatremia" above for list of causes of central and nephrogenic Dl

• Workup of Dl: Uo^ 300 (complete) or 300-600 (partial)

water deprivation test: deprive until P«*™ >295 and UOMn <300. then administer vasopressin (5U SC) or dDAVP (10 pig intranasal): Uotm ' by >50% central Dl Uoun unchanged nephrogenic Dl

• Treatment of Dl: see "Hypernatremia" above

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