RESUMEN
Background: The currently best-established ultrasound-guided lumbar plexus block (LPB) techniques use a paravertebral location of the probe, such as the lumbar ultrasound trident (LUT). However, paravertebral ultrasound scanning can provide inadequate sonographic visibility of the lumbar plexus in some patients. The ultrasound-guided shamrock LPB technique allows real-time sonographic viewing of the lumbar plexus, various anatomical landmarks, advancement of the needle, and spread of local anaesthetic injectate in most patients. We aimed to compare block procedure outcomes, effectiveness, and safety of the shamrock vs LUT. Methods: Twenty healthy men underwent ultrasound-guided shamrock and LUT LPBs (2% lidocaineadrenaline 20 ml, with 1 ml diluted contrast added) in a blinded randomized crossover study. The primary outcome was block procedure time. Secondary outcomes were procedural discomfort, number of needle insertions, injectate spread assessed with magnetic resonance imaging, sensorimotor effects, and lidocaine pharmacokinetics. Results: The shamrock LPB procedure was faster than LUT (238 [sd 74] vs 334 [156] s; P=0.009), more comfortable {numeric rating scale 010: 3 [interquartile range (IQR) 24] vs 4 [36]; P=0.03}, and required fewer needle insertions (2 [IQR 13] vs 6 [212]; P=0.003). Perineural injectate spread seen with magnetic resonance imaging was similar between the groups and consistent with motor and sensory mapping. Zero/20 (0%) and 1/19 (5%) subjects had epidural spread after shamrock and LUT (P=1.00), respectively. The lidocaine pharmacokinetics were similar between the groups. Conclusions: Shamrock was faster, more comfortable, and equally effective compared with LUT. Clinical trial registration: NCT02255591