title: Peripheral nerve stimulation under ultrasonographic control to determine the needle-to-nerve relationship.
abstract: OBJECTIVE
  To determine the needle-to-nerve distances during electrical nerve location in dogs at different currents and pulse duration using a peripheral nerve stimulator (PNS) under ultrasound control (US), and the minimal electrical thresholds (MET) necessary to obtain a motor response (MR) after achieving needle-to-nerve contact.
  
  
  METHODS
  Prospective in vivo experimental trial in a clinical setting
  
  
  METHODS
  Thirty dogs, scheduled for locoregional anaesthesia of the sciatic nerve.
  
  
  METHODS
  Needle-to-nerve distance was measured ultrasonographically after obtaining the MR of sciatic nerve with 2, 1 and 0.5 mA and pulse duration 0.1 ms (NS0.1). Thereafter the needle was placed in contact with the nerve and MET was determined. The procedure was repeated with 0.3 ms (NS0.3). Finally the needle was reintroduced to contact the sciatic nerve guided only by US, thus MET-US was determined. Data were analysed using Kruskal-Wallis or Mann-Whitney tests.
  
  
  RESULTS
  Needle-to-nerve distances were greater when MR was obtained with 2 mA than with 1 and 0.5 mA at 0.1 and 0.3 ms. No significant differences were observed between the needle-to-nerve distances using 0.1 or 0.3 ms. The MET [median (range)] was 0.4 (0.18-1.3) mA in NS0.1, 0.32 (0.12-0.8) mA in NS0.3; while MET-US was 0.7 (0.32-1.5) mA. When the needle contacted the nerve, the MR achieved with currents below 0.3 mA was obtained in 17.2, 40 and 0% of cases using NS0.1, NS0.3 and US respectively.
  
  
  CONCLUSIONS
  The electrical current necessary to obtain a MR decreased as the needle moved towards the nerve. However when the needle tip contacted the nerve, an MR with low current intensity could not be obtained. Thus the absence of motor response at currents below 0.3 mA cannot rule out needle-epineurium contact. When ultrasound is combined with PNS, it is more important to assess the correct needle position than searching for an MR at low currents.
authors.affiliation: Department of Veterinary Clinics, Veterinary Teaching Hospital "Mario Modenato", University of Pisa, San Piero a Grado, Pisa, Italy.
authors.forename: Diego A
authors.initials: DA
authors.lastname: Portela
authors.forename: Pablo E
authors.initials: PE
authors.lastname: Otero
authors.forename: Martina
authors.initials: M
authors.lastname: Biondi
authors.forename: Marta
authors.initials: M
authors.lastname: Romano
authors.forename: Simonetta
authors.initials: S
authors.lastname: Citi
authors.forename: Tommaso
authors.initials: T
authors.lastname: Mannucci
authors.forename: Angela
authors.initials: A
authors.lastname: Briganti
authors.forename: Gloria
authors.initials: G
authors.lastname: Breghi
authors.forename: Carlos
authors.initials: C
authors.lastname: Bollini
mesh_terms: D000818:Animals; D004285:Dogs / Q000601:surgery*; D009339:Needles / Q000662:veterinary*; D009407:Nerve Block / Q000379:methods / Q000662:veterinary; D010388:Pelvis / Q000000981:diagnostic imaging; D012584:Sciatic Nerve / Q000000981:diagnostic imaging*; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods / Q000662:veterinary*; D018084:Ultrasonography, Interventional / Q000379:methods / Q000662:veterinary*
keywords: dog; needle to nerve distance; nerve stimulation; regional anaesthesia; sciatic; ultrasound