title: Time sequence of sensory changes after upper extremity block: swelling sensation is an early and accurate predictor of success.
abstract: BACKGROUND
  Sensory assessment to estimate spread and effectiveness of a peripheral nerve block is difficult because no clinical test is specific for small sensory fibers. Occurrence of a swelling illusion (SI) during a peripheral nerve block corresponds to the impairment of small sensory fibers. The authors investigated the usefulness of SI in predicting successful peripheral nerve block by assessing the temporospatial correlation between progression of sensory impairment in cutaneous distributions anesthetized and localization of SI during peripheral nerve block installation.
  
  
  METHODS
  Interscalene, infracoracoid, or sciatic nerve blocks were performed using a nerve stimulator and 1.5% mepivacaine in 53 patients, with a total of 201 nerves to be anesthetized. Pinprick, cold, warm, touch, and proprioception were assessed every 3 min, while patients were asked to describe their perception of size and shape of their anesthetized limb and localization of these illusions. Data are presented as mean +/- SD and percentage (95% confidence interval).
  
  
  RESULTS
  Failure occurred in 12 cutaneous distributions out of a total of 201 theoretically blocked nerves. SI appeared earlier than warmth impairment (4.3 +/- 2.7 vs. 6.2 +/- 2.0 min; P < 0.05), always corresponding to successfully anesthetized cutaneous distributions, with the exception of 1 patient, who developed SI in 2 cutaneous distributions while sensory testing indicated failure in 1 distribution. SI successfully predicted the blockade of a cutaneous distribution with a sensitivity of 1.00 (0.98-1.00), a specificity of 0.92 (0.65-0.99), and an accuracy of 0.99 (0.97-1.00).
  
  
  CONCLUSIONS
  Swelling illusion may provide an early assessment of the success of a peripheral nerve block in unsedated patients.
authors.affiliation: Department of Anesthesiology, Centre Hospitalo-Universitaire Pitié-Salpêtrière, France. xavier.paqueron@psl.ap-hop-paris.fr
authors.forename: Xavier
authors.initials: X
authors.lastname: Paqueron
authors.forename: Marc E
authors.initials: ME
authors.lastname: Gentili
authors.forename: Jean Claude
authors.initials: JC
authors.lastname: Willer
authors.forename: Pierre
authors.initials: P
authors.lastname: Coriat
authors.forename: Bruno
authors.initials: B
authors.lastname: Riou
mesh_terms: D000328:Adult; D001828:Body Image; D005260:Female; D006801:Humans; D007088:Illusions / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000187:drug effects / Q000502:physiology; D009407:Nerve Block; D010147:Pain Measurement; D010525:Peripheral Nerves; D011434:Proprioception / Q000187:drug effects; D012584:Sciatic Nerve; D012677:Sensation / Q000187:drug effects; D013997:Time Factors; D034941:Upper Extremity