Effect of Mannitol on Serum Osmolality and on Water and Electrolytes Excretion

ABSTRACT

The effect of mannitol on serum osmolality(Sosm) was studied in 13 patients with increased intracranial pressure(Group I ) and 14 normal men(GroupII ). All of the Patients in Gtoup I were given 0.5 g/kg dose of mannitol radipidly and blood samples for Sosm were taken at 30 rninutes intetvals for the first one hour and at hourly intervals for the next 5 hours after mannitol infusion. Seven of Group II(Iia) received 0.5 g /kg dose of mannitol and the other 7 ( II b) received 1.0 g / kg, Blood samples for Sosm and electrolytes were taken at the same intervals for the same duration as in Group I expept for additionai blood samples every 5 rninutes during the first 30 minutes. In Group I there was no significant rise in Sosm even 30 minutes after mannitol infusion. In Group Iia and Iib, a maximum increase of 6 mOsm / kg, 14 mOsm / kg was observed at about 5 minutes, 25 minutes after mannitol infusion respectiveiy, which returned to baseline in about 1 hour and 4 hours respectively. The 1.0g /kg dose of mannitol produced a significant and relatively persistent increase in Sosm probably enough to reduce the ICP, but at dose of 0.5 g / kg there was minimal increase in Sosm; which seemed to be insufficient to reduce the ICP significantly as claimed in previous reports that there must be a Sosm rise of at least 10 mOsm / kg to have a significant reduction in ICP. Also, to detemine the loss of water and electrolytes through urine after mannitol administration, the urine volume and electrolytes were measeured at 30 minutes intervals for the first one hour and then every hour thereafter for six hours in normal men(Group II). Water and electrolytes excretion rates and urinary sodium concentrations were calculated in each interval. The author believes that these data would be useful in estimating the amount of water and electrolytes that has to be replaced.