pH adjustment of mepivacaine decreases the incidence of tourniquet pain during axillary brachial plexus anaesthesia.

The effect of pH adjustment of mepivacaine on the incidence of tourniquet pain during axillary brachial plexus anaesthesia was studied. Thirty-nine patients scheduled for hand surgery, during which use of pneumatic tourniquet for longer than 60 min was planned, were randomized into two groups. Both received axillary brachial plexus block with 40 ml, 1.4% mepivacaine, 1:200,000 epinephrine. The study group had 4 ml sodium bicarbonate (1 mEq.ml-1) added (final pH 7.31), and the control group had 4 ml saline added (final pH 5.6). The incidence of tourniquet pain was determined from cases for which tourniquet inflation lasted longer than 60 min. Tourniquet; pain was defined as poorly localized and distinct from an inadequate axillary block by a blinded observer. More tourniquet pain occurred in the control group. The authors conclude that alkalinization of mepivacaine for axillary brachial plexus anaesthesia may be indicated in cases where use of pneumatic tourniquet for long periods is planned.