title: Ilioinguinal and iliohypogastric nerves cannot be selectively blocked by using ultrasound guidance: a volunteer study.
abstract: BACKGROUND
  Ilioinguinal (IL) and iliohypogastric (IH) nerve blocks are used in patients with chronic postherniorrhaphy pain. The present study tested the hypothesis that our method, previously developed in cadavers, blocks the nerves separately and selectively in human volunteers.
  
  
  METHODS
  We blocked the IL and the IH nerves in 16 volunteers in a single-blinded randomized cross-over setting under direct ultrasound visualization, by injecting two times the ED95 volume of 1% mepivacaine needed to block a peripheral nerve. The anaesthetized skin areas were tested by pinprick and marked on the skin. A digital photo was taken. For further analysis, the parameterized picture data were transformed into a standardized and unified coordinate system to compare and calculate the overlap of the anaesthetized skin areas of the two nerves on each side. An overlap <25% was defined as selective block.
  
  
  RESULTS
  Fifty nerve blocks could be analysed. The mean volume injected to block a single nerve was 0.9 ml. Using ultrasound, we observed spread from one nerve to the other in 12% of cases. The overlap of the anaesthetized skin areas of the nerves was 60.3% and did not differ after exclusion of the cases with visible spread of local anaesthetic from one nerve to the other.
  
  
  CONCLUSIONS
  The IL and IH nerves cannot be selectively blocked even if volumes below 1 ml are used. The most likely explanation is the spread of local anaesthetic from one nerve to the other, although this could not be directly observed in most cases.
authors.affiliation: University Department of Anaesthesiology and Pain Therapy, University Hospital of Bern and University of Bern, CH-3010 Bern, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Schmutz
authors.forename: P M
authors.initials: PM
authors.lastname: Schumacher
authors.forename: C
authors.initials: C
authors.lastname: Luyet
authors.forename: M
authors.initials: M
authors.lastname: Curatolo
authors.forename: U
authors.initials: U
authors.lastname: Eichenberger
mesh_terms: D000293:Adolescent; D000328:Adult; D000779:Anesthetics, Local / Q000008:administration & dosage; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D007001:Hypogastric Plexus / Q000000981:diagnostic imaging*; D007264:Inguinal Canal / Q000000981:diagnostic imaging / Q000294:innervation; D008160:Lumbosacral Plexus / Q000000981:diagnostic imaging; D008297:Male; D008619:Mepivacaine / Q000008:administration & dosage; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D010525:Peripheral Nerves / Q000000981:diagnostic imaging* / Q000187:drug effects*; D016037:Single-Blind Method; D014463:Ultrasonography; D055815:Young Adult
chemical_list: D000779:Anesthetics, Local; D008619:Mepivacaine
keywords: chronic pain; ilioinguinal/iliohypogastric; inguinal; nerve block; ultrasonography