The estimation of minimum effective volume of 0.5% ropivacaine in ultrasound-guided interscalene brachial plexus nerve block: A clinical trial.

Background And Aims: Interscalene brachial plexus block (ISB) is the most commonly used mode of anesthesia for upper limb surgeries. Higher volume of local anesthetic used in ISB is associated with increased incidence of side effects, particularly phrenic nerve palsy. The aim of this study was to determine the minimum effective volume of 0.5% ropivacaine in 90% patients (MEV90) in ISB.

Material And Methods: With target of 45 successful cases, phase 1 clinical trial was conducted based on the principles of biased coin design up-and-down method. After obtaining Ethical Committee's approval and patient's consent, patients with American Society of Anesthesiologist physical status (ASA PS) I and II, aged 18-60 years of either sex, undergoing upper arm surgery were recruited into the study until 45 successful cases. A 7 ml of 0.5% ropivacaine was used as starting dose, with patients receiving a higher or lower dose depending on previous patient's response. R package, SPSS 23, and Microsoft Excel were used for statistical analysis.

Results: MEV90 of 0.5% ropivacaine for ISB was determined as 8.64 ml [confidence interval (CI) 95%, 8.28-9.02 ml]. Time for onset of sensory block and motor block was 5 min (5-15 min) and 10 min (5-20 min), respectively, while duration of analgesia was observed as 8.2 (4.8-12.5) h.

Conclusions: This study observes that surgical anesthesia can be accomplished with 8.64 ml (95% CI: 8.28-9.02 ml) of 0.5% ropivacaine with ultrasound-guided ISB with multiple injection technique, without clinical deterioration in block onset and duration of analgesia.