title: Unilateral spinal block for outpatient knee arthroscopy: a dose-finding study.
abstract: OBJECTIVE
  To evaluate the onset time, success rate, and recovery profile of unilateral spinal anesthesia produced with 4 mg, 6 mg, and 8 mg of 0.5% hyperbaric bupivacaine.
  
  
  METHODS
  Prospective, randomized, blinded study.
  
  
  METHODS
  Outpatient anesthesia unit at a University Hospital.
  
  
  METHODS
  90 ASA physical status I and II outpatients, who were scheduled for elective knee arthroscopy.
  
  
  METHODS
  After standard intravenous midazolam premedication (0.05 mg/kg) and crystalloid infusion (7 mL/kg) were given, patients were placed in the lateral decubitus position on the operative side, and randomly allocated to receive spinal block with either 4 mg (Group 4, n = 30), 6 mg (Group 6, n = 30), or 8 mg (Group 8, n = 30) of 0.5% hyperbaric bupivacaine injected slowly (3 mL/min) with the needle orifice directed toward the dependent side using a 25-gauge Whitacre needle. The lateral decubitus position was maintained for 15 minutes.
  
  
  RESULTS
  The onset time of surgical block was 13 +/- 5 minutes in Group 4 and 10 +/- 4 minutes in Group 6 (p = 0.006), and 9 +/- 4 minutes in Group 8 (p = 0.002). The maximum level of sensory block on the operative and nonoperative sides was, respectively, T(10) (T(12)-T(6)) and / (/-L(2)) in Group 4 (p = 0.0005), T(8) (T(12)-T(6)) and / (/-L(5)) in Group 6 (p = 0.0005), and T(7) (T(12)-T(5)) and / (/-T(10)) in Group 8 (p = 0.0005). A strictly unilateral sensory block was observed in 27 Group 4 patients (90%), 28 Group 6 patients (93%) and 23 Group 8 patients (77%) (p = 0.28). Complete unilateral motor block was observed in 29 Group 4 patients (97%), 28 Group 6 patients (93%), and 28 Group 8 patients (93%) (p = 0.80). No failed blocks were reported. Complete regression of spinal anesthesia required 71 +/- 20 minutes in Group 4 (range: 40 to 110 min), 82 +/- 25 minutes in Group 6 (range: 30 to 160 min), and 97 +/- 37 minutes in Group 8 (range: 50 to 120 min) (p = 0.003).
  
  
  CONCLUSIONS
  Hyperbaric bupivacaine 4 mg injected slowly through pencil-point directional needles in patients who are maintained in the lateral decubitus position for 15 minutes provided a surgical block that was mostly restricted to the operative side and adequate to perform knee arthroscopy, with a faster recovery profile than when a 6 mg or 8 mg dose was used.
mesh_terms: D000328:Adult; D000556:Ambulatory Surgical Procedures; D000762:Anesthesia Recovery Period; D000775:Anesthesia, Spinal; D000779:Anesthetics, Local / Q000008:administration & dosage; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000627:therapeutic use; D001182:Arthroscopy; D002045:Bupivacaine / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007022:Hypotension / Q000139:chemically induced; D007660:Ketoprofen / Q000627:therapeutic use; D007717:Knee / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010149:Postoperative Pain / Q000188:drug therapy; D011446:Prospective Studies; D016896:Treatment Outcome
chemical_list: D000779:Anesthetics, Local; D000894:Anti-Inflammatory Agents, Non-Steroidal; D007660:Ketoprofen; D002045:Bupivacaine