title: Optimal volume of local anaesthetic for adductor canal block: using the continual reassessment method to estimate ED95.
abstract: BACKGROUND
  Theoretically, the ideal volume of local anaesthetic for adductor canal block (ACB) would ensure sufficient filling of the canal and avoid proximal spread to the femoral triangle. In this dose-finding study, we aimed to investigate the minimal effective volume for an ACB needed to fill the adductor canal distally in at least 95% of patients (ED95).
  
  
  METHODS
  We performed a blinded trial, enrolling 40 healthy men. All subjects received an ACB with lidocaine 1%. Volumes were assigned sequentially to the subjects using the continual reassessment method followed by Bayesian analysis to determine the ED95. Distal filling of the adductor canal was assessed by magnetic resonance imaging (primary outcome). Secondary outcomes were the effect of volume on proximal spread to the femoral triangle (also assessed by magnetic resonance imaging), quadriceps muscle weakness (decrease by ≥25% from baseline) and sensory block.
  
  
  RESULTS
  The ED95 was 20 ml, with an estimated probability of sufficiently filling the canal of 95.1% (95% credibility interval: 0.91-0.98). Proximal spread to the femoral triangle was seen in 0/4 (0%), 7/12 (58%), 4/8 (50%), and 8/16 (50%) subjects with the 5, 10, 15, and 20 ml doses, respectively (P=0.25). Seven subjects had a reduction in muscle strength, but there was no difference between groups (P=0.85).
  
  
  CONCLUSIONS
  For an ACB, the dose closest to the ED95 needed to fill the adductor canal distally was 20 ml. There was no significant correlation between volume and proximal spread or muscle strength.
  
  
  BACKGROUND
  NCT02033356.
authors.affiliation: Department of Anaesthesia 4231, Centre of Head and Orthopaedics, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark pia.therese.jaeger@regionh.dk.
authors.forename: P
authors.initials: P
authors.lastname: Jæger
authors.affiliation: Department of Anaesthesia.
authors.forename: M T
authors.initials: MT
authors.lastname: Jenstrup
authors.affiliation: Department of Anaesthesia.
authors.forename: J
authors.initials: J
authors.lastname: Lund
authors.affiliation: The Research Unit for General Practice and Section of General Practice, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: V
authors.initials: V
authors.lastname: Siersma
authors.affiliation: Department of Radiology, Aleris-Hamlet Hospitals Copenhagen, Copenhagen, Denmark.
authors.forename: V
authors.initials: V
authors.lastname: Brøndum
authors.affiliation: Department of Anaesthesia 4231, Centre of Head and Orthopaedics, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark.
authors.forename: K L
authors.initials: KL
authors.lastname: Hilsted
authors.affiliation: Department of Anaesthesia 4231, Centre of Head and Orthopaedics, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen Ø, Denmark.
authors.forename: J B
authors.initials: JB
authors.lastname: Dahl
mesh_terms: D000293:Adolescent; D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D006801:Humans; D008012:Lidocaine / Q000008:administration & dosage* / Q000493:pharmacokinetics / Q000494:pharmacology; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D053580:Muscle Strength / Q000187:drug effects; D009407:Nerve Block / Q000009:adverse effects / Q000379:methods*; D011446:Prospective Studies; D055815:Young Adult
chemical_list: D000779:Anesthetics, Local; D008012:Lidocaine
keywords: anaesthetics, local; knee; muscle strength; nerve block