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Ovid: Oxford Handbook of Acute Medicine

Editors: Ramrakha, Punit S.; Moore, Kevin P. Title: Oxford Handbook of Acute Medicine, 2nd Edition Copyright ©1997,2004 Oxford University Press (Copyright 1997, 2004 by Punit S Ramrakha and Kevin P Moore) > Table of Contents > Chapter 9 – Endocrine emergencies > Polyuria Polyuria Definition: >3 litres urine per day. Presentation

  • Confusion (hyponatraemia or dehydration)
  • Coma
  • Proteinuria on screening
  • Depression or other psychiatric manifestations
  • Renal stones.

Causes

  • Excessive fluid intake
  • Endocrine dysfunction (DM, diabetes insipidus, hypercalcaemia)
  • Hypokalaemia
  • Intrinsic renal disease (polycystic kidneys, analgesic nephropathy, medullary cystic disease, amyloidosis) or renal recovery from ATN. Post obstructive, e.g. after catheterization of patient in chronic retention. Post renal artery angioplasty
  • Drugs (frusemide, alcohol, lithium, amphotericin B, vinblastine, demeclocycline, cisplatinum).

History

  • Duration and severity (nocturia, frequency, water consumption at night)
  • FH of diabetes mellitus, polycystic kidneys, renal calculi
  • Drug history (diuretics, analgesics, lithium, etc., see above)
  • Renal calculi (hypercalcaemia)
  • Weakness (low potassium), depression (hypercalcaemia)
  • Psychiatric history
  • Endocrine history (menses, sexual function, lactation, pubic hair)
  • Other significant pathology (e.g. causes of amyloid).

Investigations

  • U&Es (renal disease, hypokalaemia)
  • Glucose
  • Calcium, phosphate, and alkaline phosphatase
  • Plasma and urine osmolality [a U:P osmolality of <1.0 indicates diabetes insipidus, intrinsic renal disease (incl. ↓K+), or hysterical drinking]
  • AXR (nephrocalcinosis)
  • Lithium levels if appropriate
  • Dipstick protein and quantitation if indicated.

Management

  • Assess fluid status (JVP, BP, postural drop, weight charts, CVP).
  • Strict fluid balance and daily weights.
  • Insert central line to monitor the CVP.
  • Measure urinary sodium and potassium (random samples will give an indication of the loss of sodium or potassium initially, and if losses are great, accurate timed samples of <6 hours are possible).
  • P.603

  • Replace fluid losses as appropriate to maintain a normal homeostasis, using combinations of saline and dextrose.
  • Monitor potassium, calcium, phosphate, and magnesium daily or twice daily if necessary.
  • If lithium toxicity is present, see P820.
  • Avoid chasing fluids. At some point a clinical judgement has to be made to stop replacing urinary losses with iv fluids to allow the patient to reach their ‘normal equilibrium’. Once the patient is optimally hydrated then avoid replacing fluids iv to allow physiological homeostasis to occur.
  • If diabetes insipidus suspected, arrange water deprivation test (see below).

Water deprivation test

  • Stop all drugs the day before the test; no smoking or caffeine
  • Supervise the patient carefully to prevent surreptitious drinking
  • Empty the bladder after a light breakfast. No further fluids po
  • Weigh the patient at time 0, 4, 5, 6, 7, 8 hours into the test (stop the test if >3% of body weight is lost)
  • Measure serum osmolality at 30 minutes, 4 hours, and hourly till end of the test (check that the plasma osmolality rises to >290mosmol/kg to confirm an adequate stimulus for ADH release)
  • Collect urine hourly and measure the volume and osmolality (the volume should decrease and the osmolality rise; stop test if urine osmolality >800mosmol/kg as DI is excluded)
  • If polyuria continues, give desmopressin 20mcg intranasally at 8 hours
  • Allow fluids po (water) after 8 hours. Continue to measure urine osmolality hourly for a further 4 hours

Interpretation

  • Normal response: urine osmolality rises to >800mosmol/kg with a small rise after desmopressin
  • Cranial DI: urine osmolality remains low (>400mosmol/kg) andincreases by >50% after desmopressin
  • Nephrogenic DI: urine osmolality remains low (<400mosmol/kg) andonly rises a little (<45%) with desmopressin
  • Psychogenic polydipsia: urine osmolality rises (>400mosmol/kg) but istypically less than the normal response

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