Skin blood flow after intradermal injection of ropivacaine in various concentrations with and without epinephrine evaluated by laser Doppler flowmetry.

BACKGROUND AND OBJECTIVES

Skin blood flow changes after intradermal injection of ropivacaine in various concentrations with or without epinephrine were investigated using laser Doppler flowmetry.

METHODS

Twenty-three non-smoking, healthy, young male volunteers participated. Four test sites were used on each forearm (volar surface) in a randomized, double-blind study. Recordings were made at 20, 40, 60, and 90 minutes after intradermal injection (0.1 ml, 30-gauge needle). Injections of saline and 1% lidocaine and an untreated area served as controls. In Series 1, various concentrations of ropivacaine (1%, 0.5%, 0.375%, 0.125%, and 0.063%) were injected.

RESULTS

The data from this series showed a dose-response relationship: 1% ropivacaine provoked an increase in skin blood flow similar to saline; 0.5% and weaker concentrations of ropivacaine showed a reduction in flow compared to saline, this being more pronounced with the weakest solutions (0.125% and 0.063%). In Series 2, injection of 1:200,000 (5 micrograms/ml) epinephrine alone and injections of ropivacaine in various concentrations (1%, 0.5%, and 0.25%) with addition of epinephrine were carried out. Injection of epinephrine alone showed a flow almost as low as at the untreated control sites. Ropivacaine epinephrine injections were followed by a lower skin blood flow compared to saline, but the flow was significantly larger compared to the effect of epinephrine itself at the 20-minute recording.

CONCLUSION

The combination of ropivacaine and adrenaline did not accentuate but instead diminished the vasoconstrictive effect of epinephrine.