title: Electrical nerve stimulation using a stimulating catheter: what is the lower limit?
abstract: OBJECTIVE
  To minimize the risk of intraneural injection when performing nerve blocks, some authors caution against injecting through a needle placed with motor responses observed at nerve stimulator output settings of 0.3 mA or less. We present a case of placing a continuous cervical paravertebral catheter with brisk motor response while stimulating the catheter at 0.05 mA, with no adverse sequelae.
  
  
  METHODS
  A 56-year-old man scheduled for rotator cuff repair received a continuous cervical paravertebral block for intraoperative and postoperative pain control. A stimulating catheter was used for the block. During catheter placement, nerve stimulator output was decreased to 0.05 mA at 300 micros and the motor response remained brisk. The patient was not significantly sedated and experienced no pain during placement or with injection of 40 mL of 0.5% ropivacaine through the catheter. Narcotic drugs were not required during surgery, and the block provided excellent postoperative pain control. Catheter position was evaluated by fluoroscopy to further identify the catheter's relationship to the brachial plexus. The nerve trunks of C5 and C6 were clearly visible after 1 mL of iohexol (Omnipaque) was injected through the catheter. The catheter was removed the following day. At the follow-up visit 2 weeks later, the patient's neurological examination remained unremarkable.
  
  
  CONCLUSIONS
  We present a single case of successful placement of a stimulating catheter with no neurological injury even when motor response occurred at very low nerve stimulator output settings.
authors.affiliation: Department of Anesthesiology, College of Nursing, University of Iowa, 200 Hawkins Drive, 6-JCP, Iowa City, IA 52242, USA.
authors.forename: Merlin J
authors.initials: MJ
authors.lastname: Wehling
authors.forename: Robert
authors.initials: R
authors.lastname: Koorn
authors.forename: Courtney
authors.initials: C
authors.lastname: Leddell
authors.forename: André P
authors.initials: AP
authors.lastname: Boezaart
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage; D002404:Catheterization / Q000295:instrumentation / Q000379:methods*; D004599:Electric Stimulation Therapy / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000295:instrumentation / Q000379:methods; D010149:Postoperative Pain / Q000188:drug therapy / Q000628:therapy; D012782:Shoulder / Q000601:surgery
chemical_list: D000779:Anesthetics, Local