title: Incidence and effects of unintentional intraneural injection during ultrasound-guided subgluteal sciatic nerve block.
abstract: BACKGROUND
  The present study was conducted to determine the incidence of unintentional intraneural injection during ultrasound-guided subgluteal sciatic nerve block using a low-frequency transducer. We also observed the effects of intraneural injection using ropivacaine and mepivacaine.
  
  
  METHODS
  Enrolled in the study were 325 patients undergoing arthroscopic knee surgery, who each received a subgluteal sciatic nerve block under ultrasound guidance using 1.5% mepivacaine with 1:400,000 epinephrine or 0.5% ropivacaine. A block needle was inserted in-plane with the ultrasound transducer (5-2 MHz curved array) and advanced slowly under real-time ultrasound guidance until it was positioned immediately adjacent to the nerve. Twenty milliliters of either anesthetic was then injected to produce a circumferential spread. An ultrasound video was recorded and used to examine whether the local anesthetic was injected intraneurally. Sensory and motor blockade was evaluated for 30 mins after completion of the block. Duration of the block and any neurologic complications were also examined.
  
  
  RESULTS
  Intraneural injection was detected in 46 patients (16.3%; 95% confidence interval, 12.3%-20.3%). Onset of sensory and motor blockade was significantly faster in patients with intraneural injection than those without either mepivacaine or ropivacaine. Duration of sensory blockade was similar between patients with and without intraneural injection. No patient developed postoperative neurologic complications.
  
  
  CONCLUSIONS
  Unintentional intraneural injection occurred at an incidence rate of 16.3% for the ultrasound-guided subgluteal approach to the sciatic nerve. Intraneural injection of mepivacaine or ropivacaine hastened the onset of blockade but did not affect block duration, and it did not result in clinical neural injury in our small sample of patients.
authors.affiliation: Department of Anesthesiology, Shimane University School of Medicine, Izumo City, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Hara
authors.forename: Shinichi
authors.initials: S
authors.lastname: Sakura
authors.forename: Naomi
authors.initials: N
authors.lastname: Yokokawa
authors.forename: Saki
authors.initials: S
authors.lastname: Tadenuma
mesh_terms: D000293:Adolescent; D000328:Adult; D000577:Amides / Q000008:administration & dosage / Q000009:adverse effects*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000009:adverse effects*; D001182:Arthroscopy; D002081:Buttocks; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D007267:Injections; D007564:Japan; D007717:Knee / Q000294:innervation* / Q000601:surgery; D008297:Male; D008619:Mepivacaine / Q000008:administration & dosage / Q000009:adverse effects*; D008875:Middle Aged; D009043:Motor Activity / Q000187:drug effects; D009407:Nerve Block / Q000009:adverse effects*; D017288:Pain Threshold / Q000187:drug effects; D011446:Prospective Studies; D000077212:Ropivacaine; D012584:Sciatic Nerve / Q000000981:diagnostic imaging* / Q000187:drug effects*; D013997:Time Factors; D018084:Ultrasonography, Interventional; D014741:Video Recording; D055815:Young Adult
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D000077212:Ropivacaine; D008619:Mepivacaine