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Published on: January 31, 2025
The Shamrock lumbar plexus block: A dose-finding study
Axel R Sauter1, Kyrre Ullensvang, Geir Niemi
1From the Division of Emergencies and Critical Care, Department of Anaesthesiology, Oslo University Hospital Rikshospitalet (ARS, KU, GN, LR), Department of Anaesthesiology, Lovisenberg Diakonale Hospital, Oslo, Norway (HTL), Department of Anaesthesia and Intensive Care Medicine, Aarhus University Hospital, Aarhus (TFB), Department of Anaesthesia and Intensive Care Medicine, Roskilde Hospital, University of Copenhagen, Copenhagen, Denmark (JB), and Oslo Centre for Biostatistics and Epidemiology, Research Support Services, Oslo University Hospital, Oslo, Norway (AHP).
Background:
The Shamrock technique is a new method for ultrasound-guided lumbar plexus blockade. Data on the optimal local anaesthetic dose are not available.
Objective:
The objective of this study is to estimate the effective dose of ropivacaine 0.5% for a Shamrock lumbar plexus block.
Design:
A prospective dose-finding study using Dixon's up-and-down sequential method.
Setting:
University Hospital Orthopaedic Anaesthesia Unit.
Intervention:
Shamrock lumbar plexus block performance and block assessment were scheduled preoperatively. Ropivacaine 0.5% was titrated with the Dixon and Massey up-and-down method using a stepwise change of 5 ml in each consecutive patient. Combined blocks of the femoral, the lateral femoral cutaneous and the obturator nerve were prerequisite for a successful lumbar plexus block.
Patients:
Thirty patients scheduled for lower limb orthopaedic surgery completed the study.
Main Outcome Measures:
The minimum effective anaesthetic volume of ropivacaine 0.5% (ED50) to achieve a successful Shamrock lumbar plexus block in 50% of the patients. Further analysis of the data was performed with a logistic regression model to calculate ED95 and to estimate the effective doses for a sensory lumbar plexus block not requiring a motor block of the femoral nerve.
Results:
The Dixon and Massay estimate of the ED50 was 20.4 [95% confidence interval (95% CI) 13.9 to 30.0] ml ropivacaine 0.5%. The logistic regression estimate of the ED95 was 36.0 (95% CI 19.7 to 52.2) ml ropivacaine 0.5%. For a sensory lumbar plexus block, the ED50 was 17.1 (95% CI 12.3 to 21.9) ml and the ED95 was 25.8 (95% CI 18.6 to 33.1) ml.
Conclusion:
A volume of 20.4 ml ropivacaine 0.5% provided a successful Shamrock lumbar plexus block in 50% of the patients. A volume of 36.0 ml would be successful in 95% of the patients.
Trial Registration:
ClinicalTrials.gov identifier NCT01956617.
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