Acute Oliguric Renal Failure / Raised ICP
Pregnancy: Use with caution — limited data; may be used for life-threatening indications (e.g., raised ICP) with specialist review
Mannitol (Osmotic Diuretic — Renal/Neurological)
Brand names: Osmofundin 15%, Mannitol 20%
Adult dose
Dose: Cerebral oedema/raised ICP: 0.25-2 g/kg IV over 15-30 minutes. Oliguria in ATN: 200-400 mL of 20% mannitol IV (test dose first). Perioperative prevention of AKI (major surgery): 0.5-1 g/kg IV.
Route: Intravenous infusion
Frequency: Every 6-8 hours (ICP control); single doses (AKI prevention)
Max: 200 g/day (ICP); monitor osmolality
Osmotic diuretic — not metabolised, freely filtered, not reabsorbed. Use large-bore IV access or central line — can precipitate in cold or low concentrations. WARM to 37 degrees C if crystallised. Must use filter (0.45 micron) for 20% solution.
Paediatric dose
Dose: 0.25-0.5 g/kg
Route: IV infusion over 15-30 minutes
Frequency: Every 6-8 hours for ICP
Max: 2 g/kg per dose
Neonates: seek specialist opinion — use caution due to osmotic shifts. BNFc for age-specific guidance.
Dose adjustments
Renal
CONTRAINDICATED in established oliguric AKI unresponsive to a test dose (mannitol accumulates and worsens fluid overload and hypernatraemia). If no urine output after a test dose of 200 mL 20% mannitol — do NOT continue.
Hepatic
No dose adjustment required
Paediatric weight-based calculator
Neonates: seek specialist opinion — use caution due to osmotic shifts. BNFc for age-specific guidance.
Clinical pearls
- The test dose principle: before committing to mannitol for oliguric renal failure, give 200 mL of 20% mannitol IV. If urine output does not increase within 2 hours — the kidney is not responding (established ATN) and further mannitol will accumulate, causing fluid overload and hypernatraemia. STOP.
- Osmolal gap monitoring: measure serum osmolality and calculated osmolality (2xNa + glucose + urea). Osmolal gap >10 mOsm/kg suggests mannitol accumulation — reduce or stop dosing.
- ICP management (neurosurgical): mannitol reduces ICP by extracting water from brain parenchyma via osmotic gradient. Target serum osmolality 310-320 mOsm/kg. Above 320 mOsm/kg, risk of paradoxical ICP rise and renal failure.
- Mannitol vs hypertonic saline for ICP: both reduce ICP acutely. Hypertonic saline (3-23.4%) is preferred in haemodynamically unstable patients, hypovolaemia, or when repeated doses needed. Mannitol causes initial hypotension followed by diuresis.
- Perioperative AKI prevention: mannitol is sometimes given before aortic cross-clamping or renal transplant reperfusion — evidence is modest, but maintains tubular flow during ischaemia-reperfusion.
Contraindications
- Established oliguric AKI unresponsive to test dose
- Severe dehydration
- Active intracranial bleeding (unless raised ICP concurrent)
- Severe pulmonary oedema/heart failure
- Hypersensitivity to mannitol
Side effects
- Fluid overload if oliguric (mannitol pulls water into intravascular space before renal clearance)
- Hypernatraemia (osmotic effect)
- Hyperosmolality (osmolal gap monitoring needed)
- Rebound ICP rise (rebound cerebral oedema with prolonged use)
- Hyponatraemia (dilutional — early)
- Acute pulmonary oedema
Interactions
- Lithium — mannitol increases lithium renal clearance (lowers levels)
- Nephrotoxic drugs — avoid during mannitol use in pre-renal/AKI settings
Monitoring
- Urine output (hourly)
- Serum osmolality and osmolal gap
- Serum sodium
- Fluid balance
- ICP monitoring (neurocritical care)
- Renal function (creatinine/eGFR)
Reference: BNFc; BNF 90; BNFc; NICE Head Injury Guidelines; Neurocritical Care Society ICP Guidelines; SPC Mannitol 20%. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators