THE RELATIONSHIP OF TACHYPHYLAXIS IN EPIDURAL ANESTHESIA AND CSF pH CHANGE

本研究旨在阐明硬膜外麻醉中快速反应的作用机制。假设反复使用大剂量局麻药可使脑脊液pH升高，导致脑脊液pH调节失败，导致脑脊液pH升高，从而阻止局麻药分子的非统一形式经硬膜流入。然后可能发生突然的快速反应。虽然，我们证明细胞外灌注普鲁卡因导致小龙虾巨轴突pHi仅增加1-4 mM，但硬膜外给予2-5%普鲁卡因溶液不影响大鼠脑脊液pH。并且由于硬膜外导管在大鼠硬膜外腔内难以固定，我们无法在大鼠身上实现稳定的硬膜外麻醉，因此在大鼠身上没有观察到速敏反应的证据。对于硬膜外普鲁卡因对脑脊液pH值没有影响，我们认为可能是由于大鼠脑脊液体积过大，不受硬膜外小剂量普鲁卡因的影响，或者是硬膜外普鲁卡因流入量没有我们预期的那么大。

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.