Intraneural injection of local anesthetic (LA) during peripheral nerve block performance has been found to be a rather common occurrence. We examined some of the variables recorded in an ongoing trial of intraneural vs. perineural injection of LA for sciatic nerve block.
Patients were randomly assigned to intra- or perineural injection of LA. Ultrasound images were evaluated by attending anesthesiologists and an independent investigator. Expansion of sciatic nerve diameters was measured as a ratio of post-injection over pre-injection values.
The incidence of unintended intraneural injection was 10% in this case series. Concordance between operators’ judgment and post-hoc evaluation of intraneural vs. perineural LA deposition was high (Cohen's kappa = 0.914). The mean maximum change in sciatic nerve diameter was 1.46 (1.14–1.78) after intraneural injection; 1.13 (0.99–1.26) after perineural injection.
In the controlled setting of a clinical trial, anesthesiologists showed higher ability to predict intraneural injection of LA using images alone than seen in observational data based on electrical stimulation.