ADDITION OF BICARBONATE TO PLAIN BUPIVACAINE DOES NOT SIGNIFICANTLY ALTER THE ONSET OR DURATION OF PLEXUS ANESTHESIA

Background and Objectives. In an effort to elucidate further the effec t of alkalinization of bupivacaine on its anesthetic effect, a study w as undertaken using alkalinized and non-alkalinized bupivacaine for lu mbar plexus block and comparing the results with those obtained previo usly with brachial plexus block. Methods. Thirty consenting adult pati ents about to undergo lower extremity surgery under regional anesthesi a were selected for the study. All of the patients received an inguina l paravascular lumbar plexus block (''3-in-1 block''), along with a sc iatic block to allow the anticipated surgery to be carried out. The pa tients were divided into two groups, one receiving plain ''alkalinized '' 0.5% bupivacaine; the other receiving plain ''non-alkalinized'' 0.5 % bupivacaine. After each lumbar plexus block, the onset and duration of analgesia and anesthesia of the nerves derived from the lumbar plex us were determined by an independent investigator who was unaware of w hich solution had been administered. Results. There was no statistical ly significant difference between the two groups with respect to the o nset or duration of anesthesia and analgesia. Conclusions. The data ob tained in the present study indicate that alkalinization of non-epinep hrine-containing bupivacaine does not reduce the latency or increase t he duration of analgesia or anesthesia after lumbar plexus block. Sinc e most of the studies that do show such an effect of alkalinization we re carried out using epinephrine-containing bupivacaine, it is postula ted that in those studies alkalinization contributed to the decrease i n latency and increase in duration, not so much by providing an increa sed amount of local anesthetic in the free base form, but by reactivat ing epinephrine's vasoconstrictor activity, which is inactivated by a low pH.