Serious condition which can arise after relief of bilateral renal obstruction or solitary kidney obstruction with potential for severe dehydration and electrolyte disturbances (hypo and hyperkalaemia, hyponatraemia, hypomagnesaemia)
Risk factors:
- Renal impairment secondary to bilateral obstruction or solitary kidney obstruction
- Fluid overload
Definitions vary:
- > 200 mL / hr urine output for consecutive hours (2 – 4)
- > 3 L urine output / day
Physiological diuresis:
- Response to the fluid overload state – removal of the accumulated fluid and solutes which have built up during renal obstruction
- Usually resolves within 48 hours
Pathological diuresis:
- Ongoing salt and water loss beyond homeostasis – dysfunction of the tubules with inappropriate salt and water handling
- Inability to generate solute gradient in the tubules
- Excess urea and sodium in the tubules prevents water reabsorption
- Inability to maintain solute gradient in the tubules
- Excess medullary blood flow
- Increased endogenous production of ANP
- Poor response / decreased sensitivity of the collecting duct to respond to ADH
Management:
- Strict urine output monitoring and fluid balance monitoring
- Close BP monitoring including postural BPs
- Daily weights and fluid status assessments
- Daily or BD bloods and electrolytes
- Most cases are self-limiting
- If diuresis confirmed options are:
- Oral replacement in a mentally competent patient
- If can’t keep up orally – IV replacement with half normal saline at last hour’s output minus 200, or 50 %