Ropivacaine in ultrasound-guided femoral nerve block: what is the minimal effective anaesthetic concentration (EC90)?

Authors: Taha AM et al

Abstract

The objective of this study was to estimate the minimal effective anaesthetic concentrations of ropivacaine required to block the femoral nerve in 90% of patients.

Forty-five patients who had knee surgery received ultrasound-guided femoral nerve block using 15 ml ropivacaine. The ropivacaine concentration given to a patient relied on the efficacy of the block in the previous patient, using the biased-coin design up-down sequential method.

In the event of successful block, the next patient was randomly assigned to receive either the same ropivacaine concentration or a concentration 0.02% w/v less.

In the event of a failed block, the next patient received a concentration 0.02% w/v higher.

Successful block was defined as complete sensory and motor block before surgery together with pain-free surgery. The minimal effective ropivacaine concentration was estimated to be 0.167% w/v (95% CI 0.14-0.184%). Perineural injection of 15 ml ropivacaine 0.167% w/v under ultrasound guidance can provide successful femoral nerve block in 90% of patients.