title: Brief report: The sensitivity of motor responses for detecting catheter-nerve contact during ultrasound-guided femoral nerve blocks with stimulating catheters.
abstract: BACKGROUND
  We determined the sensitivity of motor responses evoked by stimulating catheters in determining catheter-nerve contact using ultrasonography as reference.
  
  
  METHODS
  Femoral nerves were contacted using stimulating catheters under ultrasonography scanning in 25 patients. The output current was increased from its minimum until quadriceps muscle contraction occurred. The sensitivity of the motor response in determining catheter-nerve contact was calculated using 0.5 mA as current threshold.
  
  
  RESULTS
  The current required for catheter stimulation to evoke a motor response ranged between 0.18 and 2.0 mA. Muscle contraction in response to 0.5 mA occurred in 16 of 25 subjects. The sensitivity of motor response for nerve stimulation was 64% (95% confidence interval: 0.43, 0.82).
  
  
  CONCLUSIONS
  The absence of muscle responses at a stimulating current≤0.5 mA does not necessarily indicate the absence of catheter-nerve contact.
authors.affiliation: Department of Anesthesiology, School of Medicine, Pontificia Universidad Católica de Chile, Marcoleta 367, 8330024, Santiago, Chile. fernando.altermatt@gmail.com
authors.forename: Fernando R
authors.initials: FR
authors.lastname: Altermatt
authors.forename: Marcia A
authors.initials: MA
authors.lastname: Corvetto
authors.forename: Camila
authors.initials: C
authors.lastname: Venegas
authors.forename: Ghislaine
authors.initials: G
authors.lastname: Echevarría
authors.forename: Pía
authors.initials: P
authors.lastname: Bravo
authors.forename: Juan C
authors.initials: JC
authors.lastname: De la Cuadra
authors.forename: Luis A
authors.initials: LA
authors.lastname: Irribarra
mesh_terms: D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology; D002045:Bupivacaine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D002404:Catheterization / Q000379:methods; D057785:Catheters; D004558:Electric Stimulation; D005260:Female; D005267:Femoral Nerve / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D007717:Knee / Q000601:surgery; D000077554:Levobupivacaine; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009339:Needles; D009407:Nerve Block / Q000295:instrumentation*; D019637:Orthopedic Procedures; D014463:Ultrasonography
chemical_list: D000779:Anesthetics, Local; D000077554:Levobupivacaine; D002045:Bupivacaine