This is a prospective cohort based observational study including 40 patients admitted in the adult ICU at our center diagnosed as either a case of TBI/ acute stroke/ intracranial hemorrhages with a mean screening ONSD of more than 5mm under mannitol osmotherapy. ONSD were measured by a high frequency linear array probe (\>10 Hz) at the time of screening. Mannitol was then administered at doses prescribed by the treating physician over 20-30 minutes via a dedicated intravenous line. ONSDs were measured again at 30, 60 and 120 minutes after completion of administration of mannitol. Demographic data, baseline ventilator parameters of patients on mechanical ventilation, GCS and mean arterial pressure at each time points were recorded. Comparison of variables at these time points were made.