Background: Chloroprocaine is a fast-acting local anesthetic, whereas bupivacaine is a long-acting one. They have been coadministered with limited success. The objective of this study was to determine the effect of additives on the efficacy of regional blockade using chloroprocaine followed by bupivacaine.

Methods: Four groups of Sprague-Dawley rats, 20 each, were administered chloroprocaine followed by bupivacaine to induce sciatic nerve blockade. Group 1 received chloroprocaine with isotonic sodium chloride solution followed by bupivacaine and was used as a control. Group 2 received chloroprocaine with isotonic sodium chloride solution and epinephrine followed by bupivacaine with epinephrine. Group 3 received chloroprocaine with sodium bicarbonate followed by bupivacaine, and group 4 received chloroprocaine with sodium bicarbonate and epinephrine followed by bupivacaine with epinephrine. The time to onset and duration of anesthesia were measured for all 4 groups.

Results: The block using chloroprocaine followed by bupivacaine in group 1 had an onset of 2.5 mins (SD, 0.4 mins) and duration of 104 mins (SD, 16 mins). Adding epinephrine to both chloroprocaine and bupivacaine (group 2) did not significantly change the onset (2.8 mins [SD, 1.3 mins]; P = 0.35) or duration (110 mins [SD, 25 mins]; P = 0.23). With group 3, adding bicarbonate to chloroprocaine hastened the onset (1.2 mins [SD, 0.4 mins]; P < 0.0001) and shortened the duration (87 mins [SD, 13 mins]; P = 0.008). In group 4, adding bicarbonate and epinephrine to chloroprocaine and epinephrine to bupivacaine hastened the onset (1.4 mins [SD, 0.4 mins]; P < 0.0001) and increased the duration (130 mins [SD, 23 mins]; P < 0.0001).

Conclusions: Sodium bicarbonate plus epinephrine shortens the onset and prolongs the duration of a chloroprocaine-bupivacaine sciatic block in Sprague-Dawley rats.