Skin blood flow changes in response to intradermal injection of bupivacaine and levobupivacaine, assessed by laser Doppler imaging

Background and objectives: The vascular effects of local anesthetics are im portant determinants of their therapeutic activity. Drugs that vasoconstric t have the potential clinical advantages of limited systemic uptake and pro longed duration of effect. The aim of this study was to assess quantitative ly the cutaneous vasoactivity of racemic bupivacaine and one of its enantio mers, levobupivacaine. Methods: Four concentrations of each drug (0.1 mt each of 0.125%, 0.25%, 0. 5%, and 0.75%), as well as normal saline, were injected intradermally into randomly assigned sites on the forearms of 10 volunteers. We measured skin blood perfusion using laser Doppler imaging before injection and at 2.5, 10 , 20, 40, 60, and 90 minutes thereafter. Results: Both drugs produced a rapid, dose-dependent increase in skin perfu sion (P < .001). Saline also caused an increase in perfusion, although less sustained. By 40 minutes, most responses had returned to baseline levels. However, after this time, perfusion continued to decrease, below baseline, for both bupivacaine and levobupivacaine. The exception to this was 0.75% b upivacaine, the response to which was significantly higher than the same co ncentration of levobupivacaine over this later period (P < .05). Conclusions: Bupivacaine and levobupivacaine both have a biphasic effect on skin microvessels. The vasoconstriction observed after 40 minutes may occu r when the quantity of drug remaining at the administration site has decrea sed to a lower level. The continued vasodilatation caused by bupivacaine is more difficult to interpret. The results suggest that these local anesthet ics cause vasodilatation at high dr,scs and vasoconstriction at lower, subc linical doses. This hypothesis and the clinical relevance of these effects warrant further investigation.