[Tachyphylaxis in continuous epidural anaesthesia with bupivacaine 0.125% and 0.25% (author's transl)]

Based on the results in 105 patients under continual thoracic epidural analgesia differences in the dose response relationship of bolusinjections are found. While under bupivacaine 0.25% a decrease of the effectivity of additional bolusinjections can be stated, the dose response relationship does not change under bupivacaine 0.125%. Moreover the effectivity of bupivacaine 0.25% increases after an interruption of the local anaesthetic infusion. The pH-value of bupivacaine 0.25% was 6.0 and that of bupivacaine 0.125% 6.3. Even so the differences of the pH-values between the two solutions are rather small, a possible key to the problem of the dose response relationship, concerning tachyphylaxis, can be suggested. But further investigations have to show, whether the use of local anaesthetic solutions, being stable at pH-values of 7 to 8, makes the continuous epidural analgesia easier to handle for postoperative pain relief.