CAFFEINE-HALOTHANE ACCURACY IN MH TESTING

The accuracy and stability of caffeine and halothane concentrations in liquid Krebs medium were examined. Caffeine-Krebs Ringer's solution i n incremental concentrations from 0.25 to 10 mM (N=8 for each concentr ation) was serially assayed over a three-year period. Storage was at 4 degrees C. For serial testing of halothane during a five month period , halothane 1% or 3% in carbogen was bubbled through a Krebs solution, contained in muscle baths, either using a roller pump (to eliminate v aporizer back pressure) or using carbogen at a line pressure of 4-6 lb s/in(2) (27-41 kPa). Halothane in Krebs was asssyed by high pressure l iquid chromatography. Caffeine concentrations did not van for 20 weeks . From then, through 60 weeks, concentrations less than 2 mM steadily diminished; after that, through 156 weeks, only 4, 8, and 10 mM were s table. When compared to the halothane concentration in gas entering th e muscle baths, halothane concentration in Krebs was predictable regar dless of method delivery, as long as a gas analyzer indicated the prop er concentration. We conclude that caffeine solutions are stable for 2 0 weeks when refrigerated, and for three years at concentrations 4 mM or greater.