Objectives: The objective of this study was to evaluate and compare the effect of lidocaine, mepivacaine, and bupivacaine on capillary blood flow in humans over therapeutic and subtherapeutic concentrations.
Methods: The effect of each treatment in eight unmedicated male volunteers was measured in a randomized, controlled, double-blind comparison. Each participant received subcutaneous injections (total, 14), at separate sites on the abdomen, consisting of 0.2 ml lidocaine (0.05%, 0.5%, 1%, and 2%), mepivacaine (0.05%, 0.5%, 1%, and 2%), bupivacaine (0.025%, 0.25%, 0.5%, and 0.75%), saline, or saline with epinephrine (5 micrograms/ml), and at an additional site a needle stick was performed and no injection made. Cutaneous blood flow was measured with a laser Doppler capillary perfusion monitor before and for 60 minutes after these interventions.
Results: The maximum increase in cutaneous blood flow was 277 +/- 141% to 511 +/- 136% (mean +/- SE) after lidocaine, 124 +/- 110% to 316 +/- 155% after mepivacaine, and 242 +/- 193% to 725 +/- 198% after bupivacaine. The increase in blood flow depended on local anesthetic concentration: low concentrations induced minimal changes, whereas higher concentrations caused great increases in cutaneous blood flow. Injection of saline or needle stick alone increased cutaneous blood flow 285 +/- 237% and 260 +/- 121%, respectively.
Conclusions: Our findings indicate that the trauma of needle stick or saline injection produces a significant increase in cutaneous capillary blood flow. Injection of clinically useful concentrations of bupivacaine and lidocaine produced even greater increases in capillary blood flow, indicating a vasodilatory effect. Injection of the lowest concentrations of lidocaine and bupivacaine caused flow to increase to a magnitude similar to that after injection of saline. In contrast, clinically useful concentrations of mepivacaine do not increase capillary blood flow to a greater extent than saline, and lower concentrations tend to blunt the increase in blood flow, indicating a mild vasoconstrictor effect.