Equimolar doses of mannitol and hypertonic saline in the treatment of increased intracranial pressure.

OBJECTIVE: To compare the effects of equimolar doses of 20% mannitol solution and of 7.45% hypertonic saline solution (HSS) in the treatment of patients with sustained elevated intracranial pressure (ICP).

DESIGN: Parallel, randomized, controlled trial.

SETTING: Two intensive care units in a university hospital.

PATIENTS: A total of 20 stable patients with a sustained ICP of >20 mm Hg secondary to traumatic brain injury (n = 17) or stroke (n = 3).

INTERVENTIONS: A single equimolar infusion (255 mOsm dose) of either 231 mL of 20% mannitol (mannitol group; n = 10 patients) or 100 mL of 7.45% hypertonic saline (HSS group; n = 10 patients) during 20 mins of administration.

MEASUREMENTS: ICP, arterial blood pressure, cerebral perfusion pressure, blood flow velocities of middle cerebral artery using continuous transcranial Doppler, brain tissue oxygen tension, serum sodium and osmolality, and urine output during a study period of 120 mins.

MAIN RESULTS: The two treatments equally and durably reduced ICP during the experiment. At 60 mins after the start of the infusion, ICP was reduced by 45% +/- 19% of baseline values (mean +/- sd) in the mannitol group vs. 35% +/- 14% of baseline values in the HSS group. Cerebral perfusion pressure and diastolic and mean blood flow velocities were durably increased in the mannitol group, resulting in lower values of pulsatility index at the different times of the experiment (p < .01 vs. HSS). No major changes in brain tissue oxygen tension were found after each treatment. Mannitol caused a significantly greater increase in urine output (p < .05) than HSS, although there was no difference in the vascular filling requirement between the two treatments. HSS caused a significant elevation of serum sodium and chloride at 120 mins after the start of the infusion (p < .01).

CONCLUSIONS: A single equimolar infusion of 20% mannitol is as effective as 7.45% HSS in decreasing ICP in patients with brain injury. Mannitol exerts additional effects on brain circulation through a possible improvement in blood rheology. Pretreatment factors, such as serum sodium, systemic hemodynamics, and brain hemodynamics, thus should be considered when choosing between mannitol and HSS for patients with increased ICP.