Brain sodium, potassium, and osmolality: effects on anesthetic requirement.

We determined the effects of hyperkalemia, hypernatremia, hyperosmolality and hypo-osmolality on halothane requirement (MAC) in dogs. Hyperkalemia did not change cerebrospinal fluid potassium or MAC. Hypernatremia proportionately increased cerebrospinal fluid sodium and osmolality. MAC concomitantly increased 43%. Serum hyperosmolality achieved by administration of 12 and 25% dextrose increased cerebrospinal fluid osmolality without appreciably altering cerebrospinal fluid sodium or MAC. Infusion of 5% dextraose produced hypo-osmolality of blood and cerebrospinal fluid. Cerebrospinal fluid sodium was diluted and MAC was reduced by 24%.