title: Ultrasound-guided continuous interscalene block: the influence of local anesthetic background delivery method on postoperative analgesia after shoulder surgery: a randomized trial.
abstract: BACKGROUND
  Automated bolus delivery has recently been shown to reduce local anesthetic consumption and improve analgesia, compared with continuous infusion, in continuous sciatic and epidural block. However, there are few data on the influence of local anesthetic delivery method on local anesthetic consumption following interscalene blockade. This randomized, double-blind trial was designed to determine whether hourly automated perineural boluses (4 mL) of local anesthesia delivered with patient-controlled pro re nata (PRN, on demand) boluses would result in a reduction in total local anesthesia consumption during continuous interscalene blockade after shoulder surgery compared with continuous perineural infusion (4 mL/h) plus patient-controlled PRN boluses.
  
  
  METHODS
  One hundred one patients undergoing major shoulder surgery under general anesthesia with ultrasound-guided continuous interscalene block were randomly assigned to receive 0.2% ropivacaine via interscalene end-hole catheter either by continuous infusion 4 mL/h (n = 50) or as automated bolus 4 mL/h (n = 51). Both delivery methods were combined with 5 mL PRN boluses of 0.2% ropivacaine with a lockout time of 30 minutes. Postoperative number of PRN boluses, 24- and 48-hour local anesthetic consumption, pain scores, rescue analgesia (morphine), and adverse events were recorded.
  
  
  RESULTS
  There were no significant differences in either the number of PRN ropivacaine boluses or total 48 hour local anesthetic consumption between the groups (18.5 [11-25.2] PRN boluses in the continuous infusion group vs 17 [8.5-29] PRN boluses in the automated bolus group). Postoperative pain was similar in both groups; on day 2, the median average pain score was 4 (2-6) in the continuous infusion group versus 3 (2-5) in the automated bolus group (P = 0.54). Nor were any statistically significant intergroup differences observed with respect to morphine rescue, incidence of adverse events, or patient satisfaction.
  
  
  CONCLUSIONS
  In continuous interscalene blockade under ultrasound guidance after shoulder surgery, automated boluses of local anesthetic combined with PRN boluses did not provide any reduction in local anesthetic consumption or rescue analgesia, compared with continuous infusion combined with PRN boluses.
authors.affiliation: From the *Department of Anesthesiology, University Hospital of Geneva, Geneva; and †Department of Anesthesiology, Hospital de la Tour, Meyrin, Switzerland.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Hamdani
authors.forename: Olivier
authors.initials: O
authors.lastname: Chassot
authors.forename: Roxane
authors.initials: R
authors.lastname: Fournier
mesh_terms: D000328:Adult; D000368:Aged; D000577:Amides / Q000008:administration & dosage / Q000627:therapeutic use; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects / Q000627:therapeutic use*; D003422:Critical Care / Q000379:methods; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000009:adverse effects / Q000379:methods*; D010149:Postoperative Pain / Q000188:drug therapy*; D017060:Patient Satisfaction; D000077212:Ropivacaine; D012782:Shoulder / Q000601:surgery*; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional / Q000379:methods*
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine