Cutaneous blood flow following subcutaneous infiltration of lidocaine with and without the addition of adrenaline or ornipressin

: The addition of ornipressin to local anesthetics increases the duration of regional anesthesia. A dose of 0.1 unit/ml produces an increase in nerve block duration comparable to adrenaline 5 micrograms/ml. In order to suppress intraoperative bleeding higher concentrations of ornipressin have been used in infiltration anesthesia. This study was designed to examine whether an increase in ornipressin concentration above 0.1 unit/ml causes a further reduction in cutaneous blood flow. Twelve volunteers took part in the study. They received intracutaneous infiltrations of 4 ml lidocaine 0.5% in the volar aspects of both forearms (Fig. 1). The solution was either plain (= Lido) or contained adrenaline 5 micrograms/ml (Lido + A), or ornipressin 0.1 unit/ml (Lido + P1) or 0.2 unit/ml (Lido + P2). Blood flow was measured with a laser Doppler flowmeter; before the infiltration the skin was locally heated to 40 degrees C in order to obtain maximal perfusion (Flow 100); this temperature was maintained throughout the measuring period. The minimal flow after infiltration was calculated as a percentage of Flow 100. Lido caused a significant decrease in flow to 59 +/- 25% (M +/- SD). Lido + A, Lido + P1 and Lido + P2 caused further significant flow reductions, to 19 +/- 21%, 23 +/- 16% and 26 +/- 23%, respectively (Figs. 3, 4). The latency of maximal flow reduction did not differ between the four solutions (Fig. 5). The results show that in infiltration anesthesia an increase in ornipressin concentration above 0.1 unit/ml does not improve superficial vasoconstriction.