The influence of diurnal rhythms in patients with intracranial hypertension: implications for management

Decompensation of brain injured patients during the night is common and has been attributed to the retention of CO2 during sleep. When CO2 is controlled, such nocturnal decompensation needs another explanation; consequently, the records of 21 consecutive patients with acute closed head injuries and increased intracranial pressure were reviewed. There were 185 separate episodes of intracranial hypertension (30 mm Hg or more for 10 minutes or more) in the 21 patients, 124 of which (67%) occurred between 4:00 a.m. and 9:00 a.m. (p less than 0.01). Intravenous pentobarbital (3 to 5 mg/kg) was effective in reducing the intracranial pressure (ICP) to normal levels during 104 of the 124 early morning episodes (84%), whereas mannitol was less effective (7 of 17; 41%). This suggests that an increase in brain blood volume directly related to diurnal rhythm is responsible for the increase in ICP. Severe bradycardia and systemic arterial hypertension were unreliable predictors of elevation in ICP. They preceded or accompanied less than one-fourth of the episodes.