Transient hyperaemic response to assess vascular reactivity of skin: effect of topical anaesthesia

Local anaesthetics affect blood vessels in various ways, depending upon the site of action and the drug used. There is controversy over the vascular effects of two widely used topical local anaesthetic agents, EMLA and Ametop. We used the transient hyperaemic response (THR) to the brief compression of the brachial artery to assess vascular reactivity of forearm skin after application of topical local anaesthesia.

Twenty healthy male volunteers were studied. Forearm blood flow-flux was measured using laser Doppler flowmetry, and the magnitude of the hyperaemic response to brachial artery occlusion for 20 s was recorded. Control cream, EMLA, or Ametop were applied and covered with an occlusive dressing for 60 min. Blood flow-flux and the hyperaemic response measurements were then repeated, with the laser Doppler probes sited over the areas of skin to which the local anaesthetic creams had been applied. Measurements were made at 60, 90, and 120 min after the application of the creams. The THR ratio (THRR) was calculated at each time point, defined as the net hyperaemic flow-flux divided by the baseline flow-flux.

At 60 min, Ametop caused a significantly greater increase in blood flow and decrease in THRR over control than EMLA [net increase of mean blood flow (SD) over control 95 (61) vs 2 (17) AU (P<0.001), net mean THRR decrease over control 1.33 (1.85) vs -0.34 (1.33) (P<0.02)].

The application of topical Ametop decreases microvascular tone and vasoreactivity of the forearm skin in healthy volunteers.