The effect of topically applied anaesthetics (EMLA® cream) on thresholds to thermode and argon laser stimulation

Abstract

The cold and warmth thresholds to thermode stimulation and the sensory and pain thresholds to argon laser stimulation were determined before and after topical application of EMLA (Eutectic Mixture of Local Anaesthetics) cream. The sensory threshold to argon laser stimulation and warmth threshold to thermode stimulation are both described in terms of warmth or faint heat. The sensory threshold persisted for more than 80 min of EMLA application, whereas the warmth and cold thresholds were detectable after 105 min in half the volunteers. Pain evoked by strong laser pulses was abolished after 80 min of cream application. The analgetic effect of topically applied lidocaine/prilocaine, evaluated by the cutaneous thermal and pain threshold, is compatible with the idea that topical application of EMLA cream blocks free nerve endings rather than the nerve fibres, and induces a sequence of sensory loss which, in some respects, differs from that typically observed after perineural application of local anaesthetics. The effect of topically applied anaesthetics is influenced by a number of thermodynamical, anatomical, and physiological factors in the skin.