title: Effects of age on minimum effective volume of local anesthetic for ultrasound-guided supraclavicular brachial plexus block.
abstract: BACKGROUND
  Involutional changes of peripheral nervous system occur with aging. The aim of the study was to determine the minimum effective volume of local anesthetic required to offer an effective ultrasound-guided supraclavicular brachial plexus block in 50% of middle-aged (< 50 years) and elderly (> 65 years) patients. We hypothesized reduced minimum effective volume of local anesthetic in elderly patients.
  
  
  METHODS
  Middle-aged (n = 22) and elderly (n = 22) patients undergoing upper limb surgery received an ultrasound-guided supraclavicular brachial plexus block. Structural analysis of the brachial plexus in supraclavicular region was obtained by measuring the cross-sectional area. The prospective, observer-blinded study method is a previously validated step-up/step-down sequence model where the local anesthetic volume for the next patient is determined by the outcome of the previous block. The starting volume was 30 ml (50 : 50 mixture, 0.5%wt/vol levobupivacaine, 2%wt/vol lidocaine). The minimum effective volume of local anesthetic was determined using Dixon and Masey method.
  
  
  RESULTS
  The minimum effective local anesthetic volume significantly differed between middle-aged and elderly [23.0 ml, 95% confidence interval (CI) 13.7-32.3 vs. 11.9 ml, 95% CI 9.3-14.6; 95% CI of the difference 1.6-20.6, P = 0.027]. The cross-sectional area of brachial plexus was 0.95 ± 0.15 in middle-aged and 0.51 ± 0.06 cm(2) in elderly patients (P < 0.001).
  
  
  CONCLUSIONS
  Within the present study, we report a reduced minimum effective anesthetic volume for ultrasound-guided supraclavicular block in elderly patients. Additionally, smaller cross-sectional surface area of brachial plexus in the supraclavicular region was observed.
authors.affiliation: Department of Anesthesiology and Intensive Care, University Hospital Merkur, Zagreb, Croatia. jadranka.pavicic-saric@st.t-com.hr
authors.forename: Jadranka
authors.initials: J
authors.lastname: Pavičić Šarić
authors.forename: Vinko
authors.initials: V
authors.lastname: Vidjak
authors.forename: Katarina
authors.initials: K
authors.lastname: Tomulić
authors.forename: Jelena
authors.initials: J
authors.lastname: Zenko
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000494:pharmacology; D001132:Arm / Q000000981:diagnostic imaging / Q000601:surgery; D001917:Brachial Plexus / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000254:growth & development; D002045:Bupivacaine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D005260:Female; D006801:Humans; D000077554:Levobupivacaine; D008012:Lidocaine / Q000008:administration & dosage* / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D011446:Prospective Studies; D012782:Shoulder / Q000000981:diagnostic imaging; D016037:Single-Blind Method; D018084:Ultrasonography, Interventional
chemical_list: D000779:Anesthetics, Local; D004338:Drug Combinations; D008012:Lidocaine; D000077554:Levobupivacaine; D002045:Bupivacaine