Objective: To determine the effect of out-of-hospital mannitol administration on systolic blood pressure (BP) in the head-injured multiple-trauma patient.Methods: This was a prospective, randomized, double-blind, placebo-controlled clinical trial involving a university-based helicopter air medical service and level-1 trauma center hospital. Endotracheally intubated head-trauma victims with Glasgow Coma Scale (GCS) scores c 12 were enrolled from November 22, 1991, to November 20, 1992, if evaluated by the participating aeromedical transport team within 6 hours of injury. Patients were excluded if they were e l 8 years old, had already received mannitol or another diuretic, were potentially pregnant, or were receiving CPR. All patients were intubated prior to study drug (mannitol [l g/ kg] or normal saline) use. Pulse and BP yere measured every 15 minutes for 2 hours following study drug administration.Results: A total of 44 patients were enrolled. After exclusion of 3 patients who did not meet all inclusion criteria, there were 20 patients in the mannitol group and 21 patients in the placebo group. The groups were similar at baseline in age, pulse, systolic BP (baseline mannitol: 124 t 47 mm Hg; placebo: 128 2 32 mm Hg), GCS score, and Injury Severity Scale score. Systolic BP did not change significantly throughout the observation period in either group. This study had 83% power to detect a mean systolic BP drop to <90 mm Hg. Conclusion:Out-of-hospital administration of mannitol did not significantly change systolic BP in this group of head-injured multigle-trauma patients.Key words: head injury; brain injury; mannitol; emergency medical services; patient transport; hemodynamics-blood pressure. I The most common cause of death in the UnitedStates among persons aged 1-44 years is injury. ~p -proximately 50% of all trauma deaths are due to head injury,' and there are about 19 head-injury deaths annually per ~00,000 U.S. residents.2 At the present time, the optimal treatment for severe head injury is unknown.One of the mechanisms for the high morbidity and mortality associated with head injury is a rise in intra- Center;