title: Effect of local anaesthetic volume (20 vs 5 ml) on the efficacy and respiratory consequences of ultrasound-guided interscalene brachial plexus block.
abstract: BACKGROUND
  Interscalene brachial plexus block (ISBPB) is an effective nerve block for shoulder surgery. However, a 100% incidence of phrenic nerve palsy limits the application of ISBPB for patients with limited pulmonary reserve. We examined the incidence of phrenic nerve palsy with a low-volume ISBPB compared with a standard-volume technique both guided by ultrasound.
  
  
  METHODS
  Forty patients undergoing shoulder surgery were randomized to receive an ultrasound-guided ISBPB of either 5 or 20 ml ropivacaine 0.5%. General anaesthesia was standardized. Both groups were assessed for respiratory function by sonographic diaphragmatic assessment and spirometry before and after receiving ISBPB, and after surgery. Motor and sensory block, pain, sleep quality, and analgesic consumption were additional outcomes. Statistical comparison of continuous variables was analysed using one-way analysis of variance and Student's t-test. Non-continuous variables were analysed using chi(2) tests. Statistical significance was assumed at P<0.05.
  
  
  RESULTS
  The incidence of diaphragmatic paralysis was significantly lower in the low-volume group compared with the standard-volume group (45% vs 100%). Reduction in forced expiratory volume in 1 s, forced vital capacity, and peak expiratory flow at 30 min after the block was also significantly less in the low-volume group. In addition, there was a significantly greater decrease in postoperative oxygen saturation in the standard-volume group (-5.85 vs -1.50, P=0.004) after surgery. There were no significant differences in pain scores, sleep quality, and total morphine consumption up to 24 h after surgery.
  
  
  CONCLUSIONS
  The use of low-volume ultrasound-guided ISBPB is associated with fewer respiratory and other complications with no change in postoperative analgesia compared with the standard-volume technique.
authors.affiliation: Department of Anesthesia, Sunnybrook Health Sciences Center, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario, Canada M4N 3M5.
authors.forename: S
authors.initials: S
authors.lastname: Riazi
authors.forename: N
authors.initials: N
authors.lastname: Carmichael
authors.forename: I
authors.initials: I
authors.lastname: Awad
authors.forename: R M
authors.initials: RM
authors.lastname: Holtby
authors.forename: C J L
authors.initials: CJ
authors.lastname: McCartney
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000701:Analgesics, Opioid / Q000008:administration & dosage; D000779:Anesthetics, Local / Q000008:administration & dosage* / Q000009:adverse effects; D001917:Brachial Plexus / Q000000981:diagnostic imaging*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage; D009407:Nerve Block / Q000009:adverse effects / Q000379:methods*; D010147:Pain Measurement / Q000379:methods; D010149:Postoperative Pain / Q000517:prevention & control; D010791:Phrenic Nerve / Q000293:injuries; D012131:Respiratory Insufficiency / Q000209:etiology / Q000517:prevention & control; D012133:Respiratory Paralysis / Q000209:etiology* / Q000517:prevention & control; D012785:Shoulder Joint / Q000601:surgery; D018084:Ultrasonography, Interventional / Q000379:methods*
chemical_list: D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D009020:Morphine