title: Real-time evaluation of diffusion of the local anesthetic solution during peribulbar block using ultrasound imaging and clinical correlates of diffusion.
abstract: OBJECTIVE
  The aims of this prospective observational study were to assess the incidence of intraconal spread during peribulbar (extraconal) anesthesia by real-time ultrasound imaging of the retro-orbital compartment and to determine whether a complete sensory and motor block (with akinesia) of the eye is directly related to the intraconal spread.
  
  
  METHODS
  Ultrasound imaging was performed in 100 patients who underwent a surgical procedure on the posterior segment of the eye. All patients received a peribulbar block using the inferolateral approach. Once the needle was in place, a linear ultrasound transducer was placed over the eyelid and the spread of local anesthetics was assessed during the injection (real time). Akinesia was assessed by a blinded observer 10 minutes after block placement. The incidence of intraconal spread and its correlation with a complete akinesia was measured.
  
  
  RESULTS
  The overall block failure rate was 28% in terms of akinesia, and the rate of rescue blocks was 20%. Clear intraconal spread during injection of the local anesthetic mixture could be detected with ultrasound imaging in 61 of 100 patients. The positive predictive value for successful block when intraconal spread was detected was 98% (95% confidence interval, 91%-100%). The association between clear and no evidence of intraconal spread and effective block was statistically significant (χ test, P < 0.001).
  
  
  CONCLUSIONS
  Ultrasound imaging provides information of local anesthetic spread within the retro-orbital space, which might assist in the prediction of block success.
authors.affiliation: Department of Anesthesiology and Pain Therapy, Inselspital, University Hospital, University of Bern, Bern, Switzerland. cedric.luyet@insel.ch
authors.forename: Cédric
authors.initials: C
authors.lastname: Luyet
authors.forename: Kenneth T
authors.initials: KT
authors.lastname: Eng
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Kertes
authors.forename: Arsenio
authors.initials: A
authors.lastname: Avila
authors.forename: Rajeev H
authors.initials: RH
authors.lastname: Muni
authors.forename: Paul
authors.initials: P
authors.lastname: McHardy
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage / Q000737:chemistry*; D004058:Diffusion; D006801:Humans; D009407:Nerve Block; D013508:Ophthalmologic Surgical Procedures; D017063:Outcome Assessment, Health Care; D014465:Ultrasonics
chemical_list: D000779:Anesthetics, Local