Intra‐ and inter‐Individual variability in nerve block duration: A randomized cross‐over trial in the common peroneal nerve of healthy volunteers

Abstract

Background:The reported variation in nerve block duration is considerable. To individualize nerve block therapy, knowledge of the intra-vs inter-individual variability is essential. We investigated the relative contribution of these 2 parameters to the overall nerve block duration variability. Methods:With ethics committee approval, we conducted a randomized cross-over trial where 20 healthy volunteers received 8 common peroneal nerve blockades with lidocaine 0.5% on 4 consecutive days. Allocations were 5 mL to either the right or left side and 10 mL to the opposite side on day 1 and 2 and vice versa on day 3 and 4. With fixed needle entry and nerve target, we repeated local anaesthetic deposition for each blockade. The primary outcome was variation in duration of sensory nerve block defined as insensitivity to a cold stimulus. Data were analysed using linear mixed model regression. Results:The mean sensory block duration of 380 (95% CI = [342; 418]) minutes on day one was 55 [33; 77] minutes longer than on day two (P < .001), but there were no differences in mean duration between days 2, 3 and 4. The ratios with 2.5; 97.5 percentiles between inter-and intra-individual variation were 2.4 [0.8; 5.2] for the 5 mL blockades and 3.0 [0.9; 6.7] for the 10 mL blockades. The probabilities of inter-to intra-individual variation-ratios >1 were 96% and 97%. Conclusion: The intra-individual variability is a substantially minor contributor to the overall variability in sensory nerve block duration compared with the inter-individual variability.

Mechanisms of action of the erector spinae plane (ESP) block: a narrative review

“…[27][28][29] Interindividual and even intra-individual variation (i.e., different results are produced by the identical block technique performed at different times in the same individual) in neural sensitivity have been shown not just with fascial plane blocks (e.g., the TAP and ESP blocks) 21,[30][31][32] but also with discrete blocks of individual peripheral nerves in the upper and lower limbs. [33][34][35] Together with normal anatomical variation in the anastomotic interconnections between nerves and the course they follow, this may explain the significantly different patterns of cutaneous sensory loss observed in clinical practice. Finally, it must be noted that cutaneous sensory testing only reflects blockade of terminal nerve branches in the skin.…”