Superior effect of hypertonic saline over mannitol to attenuate cerebral edema in a rabbit bacterial meningitis model

Objective: Adjunctive therapies that reduce the cerebral edema in bacterial meningitis include osmotic agents. There is a lack of information comparing mannitol vs. hypertonic saline as an osmotic agent for adjunctive therapy of bacterial meningitis. We attempted to elucidate the impact of hypertonic saline in cerebral edema in the setting of bacterial meningitis as well as to explore potential mechanisms of action. Design: Randomized controlled in vivo study. Setting: University research laboratory. Subjects: Rabbits. Interventions: A rabbit model of bacterial meningitis was used comparing 3% hypertonic saline with 20% mannitol as adjunctive therapy. Measurements and Main Results: Adjunctive 3% hypertonic saline treatment persistently elevated mean arterial pressure as compared with the model or ampicillin group (p <.01). Although both 20% mannitol and 3% hypertonic saline efficiently elevated serum osmolality for almost 5 hrs (p <.01), 20% mannitol lowered intracranial pressure for only a short time (< 2 hrs) and did not elevate cerebral perfusion pressure. Three percent hypertonic saline treatment efficiently lowered intracranial pressure and elevated cerebral perfusion pressure for almost 5 hrs (p<. 01). Furthermore, 3% hypertonic saline treatment efficiently elevated serum Na+ concentration for > 5 hrs (p <.01). Three percent hypertonic saline treatment was superior to 20% mannitol in lowering leukocyte number and protein content in cerebrospinal fluid (p <.01). Three percent hypertonic saline treatment reduced water content and Evans blue incorporation in the brain (p <.01). Three percent hypertonic saline treatment inhibited aquaporin 4 expression (p <.01) and attenuated pathologic brain damage more efficiently compared with adjuvant 20% mannitol treatment (p <.01). Conclusions: Adjunctive 3% hypertonic saline treatment significantly elevated mean arterial pressure, reduced intracranial pressure, greatly improved cerebral perfusion pressure, inhibited brain aquaporin 4 expression, reduced cerebral edema, and attenuated brain damage with a superior effect over 20% mannitol in a rabbit bacterial meningitis model. (Crit Care Med 2011; 39: 1467-1473)