EFFECT OF INTRADERMAL INJECTION OF SALINE OR A LOCAL-ANESTHETIC AGENT ON SKIN BLOOD-FLOW - A METHODOLOGICAL STUDY IN MAN

The influence of intradermal needle insertion and fluid injection on skin blood flow was investigated using laser Doppler flowmetry. Seventeen healthy, young male volunteers participated. Four test sites on each forearm (volar surface) were used in a randomized, double-blind study. Recordings were made at 20, 40, 60 and in Group III also at 90 min after needle insertion or intradermal injection. In Group I (n = 6) different volumes of saline (0.05, 0.1, 0.2, 0.3 and 0.5 ml) were injected, producing an increase in flow, there being no differences between the various volumes. In Group II (n = 4) needle insertions were made using different needle sizes (20 G, 23 G and 30 G), the larger ones being impractical to use. Increases in flow were seen, and were somewhat higher for the larger needles. Group III (n = 12) was studied regarding the effects of three local anaesthetic agents on skin blood flow (0.1 ml, 30 G needle). Injection of bupivacaine 0.75% produced a marked increase in flow, similar to lidocaine 1% but apparently longer lasting. Bupivacaine 0.25% caused less increase in flow, similar to the flow seen with saline. Injections of ropivacaine 0.75% and 0.25%, i.e. in clinical concentrations, caused a decrease in blood flow, this being most marked after 0.25%, indicating a unique flow-decreasing effect of this new local anaesthetic drug.