THE RELATIONSHIP OF TACHYPHYLAXIS IN EPIDURAL ANESTHESIA AND CSF pH CHANGE

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This study was carried out to elucidate the mechanism of tachyphylaxis in clinical epidural anesthesia. The hypothesis was that repetitive administration of large dose local anesthetics may increase csf pH will cause failure in csf pH regulation, result in csf pH increase, which prevent transdural influx of unionized forms of local anesthetic molecule. Then abrupt tachyphylaxis may take place.Although, we demonstrated that extracellular procaine perfusion resulted in pHi increase in crayfish giant axon with only 1-4 mM,epidurally administered 2-5% procaine solution did not affect csf pH in rat. And, because of difficulty in settlement of epidural catheter in rat epidural space, we could not achieve stable epidural anesthesia in rats, so no evidence of tachypylaxis was observed in rats.As to the fact that no effect of epidural procaine on csf pH,we considered that the rat csf volume is too large to be affected by epidurally administered small dose of procaine, or transdural procaine influx is not so large as we expected.