[The effects of carbonation on 2% mepivacaine in epidural anesthesia]

To evaluate the clinical effects of 2% carbonated mepivacaine in arthroscopic surgery of the knee.

Thirty patients were enrolled in this prospective, double-blind study, and randomly assigned to two groups to receive 2% mepivacaine plus saline (group I, n = 15) or 2% mepivacaine plus bicarbonate soda. The alkalinized solution was prepared by adding 0.1 mEq of 8.4% bicarbonate soda to each ml of 2% mepivacaine. A total volume of 16 ml of the mixture assigned was injected through an epidural catheter. Variables recorded were time until sensory blockade, maximum cephalad spread, number of marked dermatomes, regression time, degree of motor blockade and time until start of surgery.

Fewer marked dermatomes were observed in group II than in group I after 5 minutes (6.5 +/- 3.3 versus 9.3 +/- 2.8), after 15 minutes (1.5 +/- 1 versus 3 +/- 2.2), at 20 minutes (1 +/- 1.1 versus 1.8 +/- 0.9) and after 25 minutes (0.4 +/- 0.7 versus 1.2 +/- 1.2) (p < 0.05). We observed no significant differences in time until start of analgesia, maximum cephalad spread of sensory blockade or degree of sensory blockade.

Alkalinization of 2% mepivacaine delivered epidurally improves the quality of blockade, decreasing time until start of surgery. However, the slight clinical significance of these results does not appear to justify general application.