title: Opening injection pressure consistently detects needle-nerve contact during ultrasound-guided interscalene brachial plexus block.
abstract: BACKGROUND
  Needle trauma may cause neuropathy after nerve blockade. Even without injection, nerve injury can result from forceful needle-nerve contact (NNC). High opening injection pressures (OIPs) have been associated with intrafascicular needle tip placement and nerve damage; however, the relationship between OIP and NNC is unclear. The authors conducted a prospective, observational study to define this relationship.
  
  
  METHODS
  Sixteen patients scheduled for shoulder surgery under interscalene block were enrolled if they had clear ultrasound images of the brachial plexus roots. A 22-gauge stimulating needle was inserted within 1 mm of the root, and 1-ml D5W injected at 10 ml/min by using an automated pump. OIP was monitored using an in-line pressure manometer and injections aborted if 15 psi or greater. The needle was advanced to displace the nerve slightly (NNC), and the procedure repeated. Occurrence of evoked motor response and paresthesia were recorded.
  
  
  RESULTS
  Fifteen patients had at least one clearly visible root. OIP at 1 mm distance from the nerve was less than 15 psi (mean peak pressure 8.2 ± 2.4 psi) and the 1-ml injection could be completed in all but two cases (3%). In contrast, OIP during NNC was 15 psi or greater (mean peak pressure 20.9 ± 3.7 psi) in 35 of 36 injections. Aborting the injection when OIP reached 15 psi prevented commencement of injection in all cases of NNC except one.
  
  
  CONCLUSIONS
  High OIP (≥15 psi) consistently detected NNC, suggesting that injection pressure monitoring may be useful in preventing injection against nerve roots during interscalene block.
authors.affiliation: From the Department of Anesthesiology, St. Luke's-Roosevelt Hospital Center, New York, New York (J.C.G. and A.R.); Department of Anesthesiology, Kaiser Permanente Santa Clara Medical Center, Santa Clara, California (J.J.C.); and Department of Anesthesiology, Bronx-Lebanon Hospital Center, Bronx, New York (E.L.).
authors.forename: Jeff C
authors.initials: JC
authors.lastname: Gadsden
authors.forename: Jason J
authors.initials: JJ
authors.lastname: Choi
authors.forename: Emily
authors.initials: E
authors.lastname: Lin
authors.forename: Allegra
authors.initials: A
authors.lastname: Robinson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001917:Brachial Plexus / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007267:Injections / Q000295:instrumentation / Q000379:methods; D008297:Male; D008875:Middle Aged; D009339:Needles; D009407:Nerve Block / Q000295:instrumentation / Q000379:methods*; D011312:Pressure; D011446:Prospective Studies; D018084:Ultrasonography, Interventional / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult