Minimum effective volume of ropivacaine 7.5 mg/ml for an ultrasound-guided infraclavicular brachial plexus block

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Abstract

Background

Ultrasound guidance has been shown to reduce the minimum effective volume (MEV) of local anaesthetics for several peripheral nerve blocks. Although the lateral sagittal infraclavicular block (LSIB) is a well-established anaesthesia method, MEV for this technique has not been established. Our aim with this study was to determine the MEV using ropivacaine 7.5 mg/ml for the LSIB method.

Methods

Twenty-five adult American Society of Anesthesiologists physical status I-II patients scheduled for hand surgery received an ultrasound-guided LSIB with ropivacaine 7.5 mg/ml. A successful block was defined as anaesthesia or analgesia for all five sensory nerves distal to the elbow, 30 min after local anaesthetic injection. The MEV for a successful block in 50% of the patients was determined by using the staircase up-and-down method introduced by Dixon and Massey. Logistic regression and probit transformation were applied to estimate the MEV for a successful block in 95% of the patients.

Results

The patients received ropivacaine 7.5 mg/ml volumes in the range of 12.5–30 ml. The MEVs in 50% and 95% of the patients were 19 ml [95% confidence interval (CI), 14–27] and 31 ml (95% CI, 18–45), respectively.

Conclusions

For surgery distal to the elbow, the MEV in 95% of patients for an ultrasound-guided LSIB with ropivacaine 7.5 mg/ml was estimated to be 31 ml (95% CI, 18–45 ml). Further studies should determine the factors that influence the volume of local anaesthetic required for a successful infraclavicular block.

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