title: Sympathetic skin response: monitoring of CT-guided lumbar sympathetic blocks.
abstract: OBJECTIVE
  To prospectively evaluate accuracy of sympathetic skin response (SSR) for monitoring computed tomography (CT)-guided lumbar sympathetic blocks, with palpable temperature increase in the foot 30 minutes after injection serving as the reference standard.
  
  
  METHODS
  Institutional review board approval and written informed consent were obtained. Seventy individual lumbar sympathetic blocks were performed in 13 patients (six female, seven male; mean age, 45 years) with reflex sympathetic dystrophy of the foot. A 22-gauge needle was advanced to the sympathetic trunk at midlumbar level with CT fluoroscopic guidance, and 1 mL of iopamidol (200 mg of iodine per milliliter) and 5 mL of 0.5% bupivacaine were injected. SSR was monitored in both feet before and after bupivacaine injection. SSRs were activated with painless low-strength (5-20-mA) electrical stimuli. SSR ratio (SSR in the injected foot versus SSR in the contralateral foot) was calculated before injection and repeatedly at 1-minute intervals thereafter. Needle tip position and distribution of bupivacaine were measured on CT images. Receiver operating characteristic curves for SSR ratio were calculated until 7 minutes after injection. Logistic regression analyses adjusted for clustering were calculated for SSR ratio, injection parameters, needle tip position, and bupivacaine distribution.
  
  
  RESULTS
  Thirty minutes after injection, 83% of procedures were considered clinically successful. An SSR cutoff ratio of 1:10 was used, and sensitivity, specificity, and accuracy of SSR for prediction of clinical success were 84%, 92%, and 86%, respectively, 4 minutes after injection and 95%, 92%, and 94%, respectively, 7 minutes after injection. Needle tip position (P = .19), medial and lateral borders of bupivacaine distribution (P = .11 and .056), and distance between bupivacaine distribution and the vertebral body (P = .41) were not significantly different between successful and unsuccessful injections.
  
  
  CONCLUSIONS
  SSR can be used to correctly identify needle tip position in lumbar sympathetic blocks 6 and 7 minutes after injection.
authors.affiliation: Department of Radiology, Department of Physical Medicine and Rheumatology, and Spinal Cord Injury Center, University Hospital Balgrist, Zurich, Switzerland.
authors.forename: Marius R
authors.initials: MR
authors.lastname: Schmid
authors.forename: Rudolf O
authors.initials: RO
authors.lastname: Kissling
authors.forename: Armin
authors.initials: A
authors.lastname: Curt
authors.forename: Gabriel
authors.initials: G
authors.lastname: Jaschko
authors.forename: Juerg
authors.initials: J
authors.lastname: Hodler
mesh_terms: D000293:Adolescent; D000328:Adult; D000775:Anesthesia, Spinal / Q000379:methods*; D000779:Anesthetics, Local / Q000008:administration & dosage; D001340:Autonomic Nerve Block / Q000379:methods*; D001831:Body Temperature; D002045:Bupivacaine / Q000008:administration & dosage; D003287:Contrast Media / Q000008:administration & dosage; D005260:Female; D005471:Fluoroscopy; D005528:Foot; D006801:Humans; D007267:Injections; D007479:Iopamidol / Q000008:administration & dosage; D016015:Logistic Models; D008161:Lumbosacral Region; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012372:ROC Curve; D015641:Radiography, Interventional; D012680:Sensitivity and Specificity; D012867:Skin / Q000294:innervation*; D014057:Tomography, X-Ray Computed
chemical_list: D000779:Anesthetics, Local; D003287:Contrast Media; D007479:Iopamidol; D002045:Bupivacaine