Mannitol in severe traumatic brain injury
Level II: mannitol is effective for control of Traumatic Intracranial Hypertension (note: current information did not allow recommendations regarding hypertonic saline to be made)
● intermittent boluses may be more effective than continuous infusion
● effective doses range from 0.25–1 gm/kg body weight
● avoid hypotension (SBP < 90mm Hg) which may result from the diuretic effect of mannitol, which can lead to ↓ circulating fluid volume
● indications: signs of transtentorial herniation or progressive neurological deterioration not attributable to systemic pathology
● euvolemia should be maintained (hypovolemia should be avoided) by fluid replacement. An indwelling urinary catheter is essential
● serum osmolarity should be kept < 320 mOsm when there is concern about renal failure
No controlled clinical trial has been conducted to show the benefits of mannitol over placebo.
The exact mechanism(s) by which mannitol provides its beneficial effects is still controversial, but probably includes some combination of the following
1. lowering ICP
a) immediate plasma expansion: reduces the hematocrit and blood viscosity (improved rheology) which increases CBF and O2 delivery. This reduces ICP within a few minutes, and is most marked in patients with CPP < 70mm Hg
With bolus administration, onset of ICP lowering effect occurs in 1–5 minutes; peaks at 20–60 minutes.When urgent reduction of ICP is needed, an initial dose of 1 gm/kg should be given over 30 minutes.When long-term reduction of ICP is intended, the infusion time should be lengthened to 60 minutes and the dose reduced (e.g. 0.25–0.5 gm/kg q 6 hrs). A large previous dose reduces the effectiveness of subsequent doses72; thus it is desirable to use the smallest effective dose (small frequent doses may be preferable, e.g. 0.25 mg/kg q 2–3 hrs; also results in fewer peaks as mannitol “troughs” are smoothed out). Titrating to ICP (instead of dosing at regular intervals) results in less mannitol being given.
The effectiveness of mannitol may be synergistically enhanced when combined with the use of loop acting diuretics (e.g. furosemide,), and alternating these medications has been suggested.