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During the routine care of neurosurgical patients with obstructive hydrocephalus, periodic drainage of the ventricles has been necessary for the relief from intracranial pressure in a number of cases. It has been noted repeatedly that in the early morning the symptoms of pressure develop much more slowly, and, furthermore, that after longer periods of time, drainage of the ventricles yields less fluid than at other times during the day. This has been observed so constantly that at present it is customary to allow these patients to go from midnight until 8 or 9 a. m. without drainage. Even then the intracranial pressure and the quantity of fluid obtained is less than after a four to six hour interval during the later part of the morning or evening.
The most striking illustration of this diurnal and nocturnal variation in the formation of ventricular fluid was given by a patient in whom
HART D. CEREBROSPINAL FLUIDNORMAL VARIATIONS IN THE RATE OF FORMATION. Arch Surg. 1927;15(6):943–957. doi:10.1001/archsurg.1927.01130240116009