Mannitol

Non-reabsorbable sugar -> osmotic diuretic

inhibits water reabsportion in proximal convuluted tubule (mainly), as well as thing descending loop and collecting ducts

Water loss>>electrolyte loss

Clinical uses:

  • early oliguria
  • early brain edema
  • postischemic acute renal failure
  • Neurosurgical anesthesia for good operating conditions

Retention of mannitol –> further volume expansion –> pulmonary edema in CHF patients.

Half life 100 minutes, with 15 minute onset to ICP reduction.

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Image courtesy of Pinterest

Intra-operative Use

I/O use for rapid reduction of brain volume.

Dose = 0.25g/kg (some evidence this works but doesn’t last as long) to infusion¬†of 100g for all. 1g/kg also used.

Infusion always, if given too fast –> hyperosmolarity –> vasodilatory effect –> brain engorgement –> increase ICP

Concerns regarding entering the parenchyma, or whether it is effective only if BBB is preserved, make some reluctant to use – best to give a test dose. If it decreases ICP / improves surgical field, then repeat.

Theoretical ‘acceptable’ upper limit of osmolarity 320 mOsm/L, but evidence is “soft” and incrimental doses of 12.5g used until no longer see a clinical response.

From Miller’s Anesthesia 2015 ch70, Anesthesia for Neurosurgery; and Pharmacology and Physiology for Anesthesia: Foundations and Clinical Application 2013.

 

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