SummaryThe vasoactive properties of EMLA (eutectic mixture of local anaesthetic) and amethocaine were compared using Doppler colour ultrasound to measure vein diameter in 20 male volunteers. EMLA or amethocaine cream were applied over veins on the dorsum of the hand and vein diameter was measured prior to application of the preparations and at 1, 1.5 and 2 h after removal. Visual analogue scores for skin colour and vasodilatation were performed at 1 h. The results showed no significant difference in vein diameter between the EMLA and amethocaine groups. However, the amethocaine-treated hands were significantly more erythematous at 1 h (p`0.00002).Keywords Anaesthetics, local; topical, EMLA, amethocaine EMLA cream (Astra Pharmaceuticals), a eutectic mixture of the two amide local anaesthetics, lignocaine and prilocaine, is a topical local anaesthetic preparation for reducing the pain of intravenous cannulation. It is generally perceived that venous cannulation is more difficult after the application of EMLA cream due to local vasoconstriction. This has been substantiated by various studies; qualitative studies have assessed skin colour and skin blanching, and have blindly scored ease of cannulation [1][2][3]. More quantitative studies have measured local blood content using Doppler colour ultrasound and blood flow using laser Doppler flowmetry [4]. However, there have been no studies in which the diameter of superficial cutaneous veins deemed suitable for venous cannulation were measured directly, and therefore the effect of EMLA on venous diameter quantified.Strategies to reduce this vasoconstrictor action include combining EMLA with venodilators such as glyceral trinitrate (GTN) and removing EMLA for a period prior to venepuncture. The combination of EMLA and GTN has been shown to increase the ease of venepuncture [3, 5]. Removal of the EMLA at some time prior to venepuncture may also be effective in improving conditions for venous cannulation, but is limited by the short duration of topical anaesthesia provided by the EMLA cream.Amethocaine is an ester local anaesthetic which is now available as a topical preparation (Ametop, Smith and Nephew). It has been shown to provide more rapid and prolonged anaesthesia compared with EMLA [6, 7] and has also been reported to have a vasodilator action, which may be a direct action of the drug, or an indirect action due to histamine release. The vascular effects of amethocaine, however, have only been measured in an observational study in which dermal colour change was recorded [8]. We carried out a study to quantify and compare the vasoactive properties of EMLA and amethocaine cream, using Doppler colour ultrasound to measure venous diameter.
MethodsAfter obtaining local ethics committee approval, 20 healthy male volunteers were recruited, gave written informed consent and took part in the study. The volunteers attended on two separate occasions at b7-day intervals. The study was a double-blind crossover design, with Anaesthesia, 1999, 54, 466-482
466ᮊ 1998 Blackwel...