Effects of hyperosmolality on the central nervous system and intracranial hemorrhage.

The relationship between hyperosmolality and intracranial hemorrhage as well as brain dysfunction was studied. Hyperosmolality was induced by continuous infusion of hyperosmotic solutions, such as 7% sodium bicarbonate (1,666 mOsm/1), 4.64% sodium chloride (1,666 mOsm/1), 20% glucose (about 1,200 mOsm/1), 20% mannitol (about 1,200 mOsm/1), and 10% glycerol with 0.9% sodium chloride and 5% fructose (about 2,000 mOsm/1). 1) Intracranial hemorrhage was observed without exception after the rabbits had died of hyperosmolality due to the infusion of these agents. The intracranial hemorrhage was mostly subdural hemorrhage in the subtentorial region. 2) The plasma osmolality just before death varied according to the agents administered and was lowest in the case of 7% sodium bicarbonate with a level of 441 mOsm/1. 3) The plasma osmolality in the case of 10% glycerol was higher than the case of 20% mannitol at the death. 4) The arousal reaction was suppressed by hyperosmotic solutions which contain sodium ions, and when the plasma osmolality surpassed 320 mOsm/1, dysfunction of the CNS began to appear. 5) The evoked muscular discharges caused by stimulation of the midbrain reticular formation were suppressed only by the administration of 7% sodium bicarbonate, so this result is related to alkalosis.