This double-blind randomized study compared the effects of an epidural injection of lidocaine hydrochloride 2% (HCi) (Group 1,k alkalinized lidocaine 2o/0 (l ml NaHCO 3 per 10 ml of solution) injected either immediately (Group 2) or one hour after preparation (Group 3) in 45 parturients (n = 15 per group) scheduled for elective Caesarean section. Each patient received 16 ml of one of the three solutions. The mean p H values measured just before administration with a pH-meter PHM 64 Met-rohm AG

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... ere 6.77 for the HCI lidocaine 2% solution, 7.34 for the freshly alkalinized solution and 7.35 for the solution prepared one hour before injection. The median maximal sensory level (range) observed was T 3 (Ta-CT,~ T4 (Ts-C~) and T 4 (Te-C~), obtained after 19 Or 6 rain, 18 Or 8 min and 16-4-6 min respectively for each group. A motor block of grade 2 or 3 on the Bromage scale was obtained in I1, 10 and 14 patients respectively. No failure was observed although 3, 5, and 2 patients in Groups 1, 2, and 3 respectively required a supplementary bolus 20 min after the initial injection because of inadequate sensory level or pain at the operative site. In conclusion, this study shows that neither fresh alkalinization of 2% iidocaine nor the delay of one hour between preparation and injection of the alkalinized solution influences the onset or quality of epidural anaesthesia for elective Caesarean section. Cette &ude randomis~e, r~alisde en double-aveugle, ,a compar~ les effets anesth~siques de la lidoca'o~e HCI 2%, de son alca-linisation immediate ~ raison de 0,1 meq par ml, et d'un d~lai d'une heure entre la preparation de la solution alcalinis$e et son injection, en c~sarienne ~lective sous anesth6sie p&idurale continue chez 45 patientes. Chaque patiente a reffz une injection pdridurale de 16 ml de la solution correspond, ant au groupe auquel eile a ~t~ attribute. Les p H moyens mesur~s &aient 6.77 pour la lidoca~ne 2% seule, 7.34 pour la solution frafche-ment alcalinis~e et 7.35 pour la solution alca~nisde prdparde l'avance. La valeur m~diane (&endue) du niveau sensitif maximal ~tait ~ D 3 (D8-C7), D 4 (Ds-C~), et D 4 (D6-C ~ obtenu aprb, s 19 • 6 minutes, 18 or 8 min et 16 + 6 rain pour les trois groupe~ respectivement. Un bloc moteur de degrd 2 ou 3 selon l'$chelle de Bromage a ~t~ obtenu chez 1I, 10 et 14 patientes respectivement. En conclusion, les r~sultats de cette &ude indiquent d'une part que ralcalinisation de la lidocafne 2o/t~ et d'autre part qu'un d~lai d'u~ heure entre ralcalinisation de la solution et son injection n'influencent pas les caract&is-tiques d'une anesth~sie p~ridurale pour c$sarierme. Epidural anaesthesia is widely performed for Caesarean section. 1.2 The literature describes several factors influencing onset, duration and quality of epidural anaesthesia in obstetrics 3 among which the most important axe: dose of local anaesthetics, volume and concentration of so-lutiom, and additives. In 1910, L~iwcn 4 observed that the addition of sodium bicarbonate 0.5% to a 1% procaine solution enhanced local anaesthetic potency and reduced omct time. The proposed mechanism of action of sodium bicarbonate is an increase in the percentage of un-ionised molecules present in the local anaesthetic solution, thus facilitating their passage through biological membranesJ ,6 Clinical studies on alkalinization of local anaesthetic solutions have provided controversial results. Some authors 6-u report a faster onset and a better quality of sensory and CAN J ANAESTH 1995 / 42:12 / pp 1080-4