Effects of Ion Concentrations
Hypernatremia increases the sodium concentration proportionately
in cerebrospinal fluid (CSF) and increases the halothane MAC in dogs by as much as
43%.[5]
Conversely, hyponatremia dilutes the CSF
sodium level and reduces the halothane MAC.[5]
Hyperkalemia in dogs does
not alter the CSF potassium level or MAC. Calcium infusions in dogs increase serum
and CSF calcium levels by 2.6 and 1.3 times, respectively, without influencing the
halothane MAC.[16]
A fivefold increase in serum
magnesium is associated with a 12% increase in CSF magnesium concentrations in dogs
and does not alter the halothane MAC.[16]
In rats,
a 10-fold increase in plasma magnesium concentration above control levels decreases
the halothane MAC by approximately 60%.[17]
Alterations
in anion concentrations by infusion of hydrochloric acid or sodium bicarbonate have
little influence on MAC despite marked changes in arterial pH.[5]
These effects of temperature, pressure, aging, and ion concentrations
may be used to test the various models of anesthetic action. Any valid theory of
anesthetic action must account for the influence of these physical and physiologic
parameters on anesthetic requirement.
