Intracranial hypertension and cerebrospinal fluid production in dogs: effects of furosemide.

A method using chronically prepared, anesthetized dogs was devised for studying the effects of treatments of intracranial hypertension induced by applying a reversible extradural mass lesion while simultaneously measuring production of cerebrospinal fluid. This was measured with a ventricular-cisternal perfusion technique in which the rate of cisternal outflow could be controlled by a pump and matched to the inflow, allowing intracranial pressure to fluctuate despite simultaneous measurement of cerebrospinal fluid formation. Elevations of intracranial pressure to the range 20 to 35 Torr were induced and maintained during perfusion, but elevations above 35 Torr would not permit continued perfusion. At normal intracranial pressure, 10 Torr or less, rates of cerebrospinal fluid formation were the same whether the outflow controlling pump or free outflow was used. Formation of cerebrospinal fluid decreased progressively as intracranial pressure increased above 20 Torr. It also decreased with time after the start of perfusion during the course of 5 h, but returned to the initial range during the control phase of subsequent experiments in the same animal. Furosemide, 3 mg kg-1, i.v., had no significant effect on rate of formation but did induce a small decrease in ICP in time-controlled experiments in which i.v. fluid replacement limited net fluid losses to 20 ml kg-1 with no change in mean arterial or central venous pressures.