Madsen MH, Christiansen CB, Mølleskov E, et al. - Since the documented variation in nerve block duration is noteworthy and given the importance of knowledge of the intra- vs inter-individual variability in order to individualize nerve block therapy, researchers compared the contribution of these 2 parameters to the overall nerve block duration variability in this randomized cross-over trial with 20 healthy volunteers. The participants were administered 8 common peroneal nerve blockades with lidocaine 0.5% on 4 consecutive days. Variation in the span of sensory nerve block (defined as insensitivity to a cold stimulus) was assessed as the primary outcome. Experts noted that on day one vs day two, the mean sensory block duration of 380 minutes was 55 minutes longer, but no differences were evident in mean duration between days 2, 3 and 4. The probabilities of inter- to intra-individual variation-ratios > 1 were estimated to be 96% and 97%. Findings highlighted a substantially minor contribution of intra-individual variability vs inter-individual variability to the overall variability in sensory nerve block duration.