title: Minimum effective volume of ropivacaine 7.5 mg/ml for an ultrasound-guided infraclavicular brachial plexus block.
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.
authors: Department of Anaesthesiology, University Hospital of North Norway, Tromsø, Norway. sandra.flohr-madsen@unn.no
authors: S
authors: S
authors: Flohr-Madsen
authors: L M
authors: LM
authors: Ytrebø
authors: S
authors: S
authors: Kregnes
authors: T
authors: T
authors: Wilsgaard
authors: Ø
authors: Ø
authors: Klaastad
mesh_terms: D000368:Aged; D000577:Amides / Q000008:administration & dosage*; D000779:Anesthetics, Local / Q000008:administration & dosage*; D001917:Brachial Plexus; D005260:Female; D006225:Hand / Q000601:surgery; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D000077212:Ropivacaine; D018084:Ultrasonography, Interventional
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine