Shamrock lumbar plexus block: A dose-finding study

Authors: Sauter A et al

European Journal of Anaesthesiology 32 (11), 764-70 (Nov 2015)

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.