title: High Opening Injection Pressure Is Associated With Needle-Nerve and Needle-Fascia Contact During Femoral Nerve Block.
abstract: OBJECTIVE
  High opening injection pressures (OIPs) have been shown to predict sustained needle tip contact with the roots of the brachial plexus. Such roots have a uniquely high ratio of fascicular versus connective tissue. It is unknown if this relationship is preserved during multifascicular nerve blockade. We hypothesized that OIP can predict needle-nerve contact during femoral nerve block, as well as detect needle contact with the fascia iliaca.
  
  
  METHODS
  Twenty adults scheduled for femoral block were recruited. Using ultrasound, a 22-gauge needle was sequentially placed in 4 locations: indenting the fascia iliaca, advanced through the fascia iliaca while lateral to the nerve, slightly indenting the femoral nerve, and withdrawn from the nerve 1 mm. At each location, the OIP required to initiate an injection of 1 mL D5W (5% dextrose in water) at 10 mL/min was recorded. Blinded investigators performed evaluations and aborted injections when an OIP of 15 psi was reached.
  
  
  RESULTS
  Opening injection pressure was 15 psi or greater for 90% and 100% of cases when the needle indented the femoral nerve and fascia iliaca, respectively. Opening injection pressure was less than 15 psi for all 20 patients when the needle was withdrawn 1 mm from the nerve as well as at the subfascial position (McNemar χ2 P < 0.001).
  
  
  CONCLUSIONS
  Opening injection pressure greater than 15 psi was associated with a block needle tip position slightly indenting the epineurium of the femoral nerve (90%) and the fascia iliaca (100%). Needle tip positions not indenting these structures were associated with OIP of less than 15 psi (100%).
authors.affiliation: From the *Department of Anesthesiology, Duke University, Durham, NC; †Department of Anesthesiology, St Luke's-Roosevelt Hospital, New York, NY; ‡Wellington Regional Hospital, Wellington, New Zealand; and §New York University, New York, NY.
authors.forename: Jeff
authors.initials: J
authors.lastname: Gadsden
authors.forename: Malikah
authors.initials: M
authors.lastname: Latmore
authors.forename: D Matt
authors.initials: DM
authors.lastname: Levine
authors.forename: Allegra
authors.initials: A
authors.lastname: Robinson
mesh_terms: D000328:Adult; D000368:Aged; D001340:Autonomic Nerve Block / Q000295:instrumentation / Q000379:methods*; D017558:Elective Surgical Procedures / Q000295:instrumentation / Q000379:methods; D005205:Fascia / Q000000981:diagnostic imaging*; D005260:Female; D005267:Femoral Nerve / Q000000981:diagnostic imaging*; D006801:Humans; D007267:Injections / Q000009:adverse effects; D008297:Male; D008365:Manometry / Q000379:methods; D008875:Middle Aged; D009339:Needles; D011312:Pressure / Q000009:adverse effects; D018084:Ultrasonography, Interventional / Q000295:instrumentation / Q000379:methods