title: Comparison of tissue distribution, phrenic nerve involvement, and epidural spread in standard- vs low-volume ultrasound-guided interscalene plexus block using contrast magnetic resonance imaging: a randomized, controlled trial.
abstract: BACKGROUND
  Ultrasound guidance allows for the use of much lower volumes of local anaesthetics for nerve blocks, which may be associated with less aberrant spread and fewer complications. This randomized, controlled study used contrast magnetic resonance imaging to view the differential-volume local anaesthetic distribution, and compared analgesic efficacy and respiratory impairment.
  
  
  METHODS
  Thirty patients undergoing shoulder surgery were randomized to receive ultrasound-guided interscalene block by a single, blinded operator with injection of ropivacaine 0.75% (either 20 or 5 ml) plus the contrast dye gadopentetate dimeglumine, followed by magnetic resonance imaging. The primary outcome was epidural spread. Secondary outcomes were central non-epidural spread, contralateral epidural spread, spread to the phrenic nerve, spirometry, ultrasound investigation of the diaphragm, block duration, pain scores during the first 24 h, time to first analgesic consumption, and total analgesic consumption.
  
  
  RESULTS
  All blocks provided fast onset and adequate intra- and postoperative analgesia, with no significant differences in pain scores at any time point. Epidural spread occurred in two subjects of each group (13.3%); however, spread to the intervertebral foramen and phrenic nerve and extensive i.m. local anaesthetic deposition were significantly more frequent in the 20 ml group. Diaphragmatic paralysis occurred twice as frequently (n=8 vs 4), and changes from baseline peak respiratory flow rate were larger [Δ=-2.66 (1.99 sd) vs -1.69 (2.0 sd) l min(-1)] in the 20 ml group.
  
  
  CONCLUSIONS
  This study demonstrates that interscalene block is associated with epidural spread irrespective of injection volume; however, less central (foraminal) and aberrant spread after low-volume injection may be associated with a more favourable risk profile.
  
  
  BACKGROUND
  This study was registered with the European Medicines Agency (Eudra-CT number 2013-004219-36) and with the US National Institutes' of Health registry and results base, clinicaltrials.gov (identifier NCT02175069).
authors: Department of Anaesthesiology, Perioperative Medicine and Intensive Care Medicine otto.stundner@gmail.com.
authors: O
authors: O
authors: Stundner
authors: Department of Radiology, Paracelsus Medical University, Müllner Hauptstrasse 48, 5020 Salzburg, Austria.
authors: M
authors: M
authors: Meissnitzer
authors: Department of Anaesthesiology, University of Michigan, 1500 E Medical Center Drive, Ann Arbor, MI, USA.
authors: C M
authors: CM
authors: Brummett
authors: Department of Anaesthesiology, University of Michigan, 1500 E Medical Center Drive, Ann Arbor, MI, USA.
authors: S
authors: S
authors: Moser
authors: Department of Radiology, Paracelsus Medical University, Müllner Hauptstrasse 48, 5020 Salzburg, Austria.
authors: R
authors: R
authors: Forstner
authors: Department of Anaesthesiology, Perioperative Medicine and Intensive Care Medicine.
authors: A
authors: A
authors: Koköfer
authors: Department of Anaesthesiology, Perioperative Medicine and Intensive Care Medicine.
authors: T
authors: T
authors: Danninger
authors: Department of Anaesthesiology, Perioperative Medicine and Intensive Care Medicine.
authors: P
authors: P
authors: Gerner
authors: Department of Anaesthesiology and Intensive Care Medicine, Trauma Hospital Salzburg, Doktor-Franz-Rehrl-Platz 5, 5010 Salzburg, Austria.
authors: L
authors: L
authors: Kirchmair
authors: Department of Anaesthesiology, Perioperative Medicine and Intensive Care Medicine.
authors: G
authors: G
authors: Fritsch
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000577:Amides / Q000493:pharmacokinetics; D000779:Anesthetics, Local / Q000493:pharmacokinetics*; D001917:Brachial Plexus / Q000000981:diagnostic imaging / Q000187:drug effects; D003287:Contrast Media; D004824:Epidural Space; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009407:Nerve Block; D010791:Phrenic Nerve / Q000187:drug effects*; D000077212:Ropivacaine; D012782:Shoulder / Q000601:surgery; D014018:Tissue Distribution; D018084:Ultrasonography, Interventional; D055815:Young Adult
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D003287:Contrast Media; D000077212:Ropivacaine; D019786:Gadolinium DTPA
keywords: anaesthetics, local; brachial plexus block; injections; intramuscular; magnetic resonance imaging; phrenic nerve