title: The influence of neck flexion and extension on the distribution of contrast medium in the high thoracic epidural space.
abstract: BACKGROUND
  For safe and effective thoracic epidural analgesia (TEA), it is important to control the level of TEA and to identify factors that influence its spread. In this study, we observed the distribution of contrast injected into the high thoracic epidural space during neck flexion and extension.
  
  
  METHODS
  An epidural catheter was inserted into the epidural space until its tip was located at the T1-2 intervertebral level. Patients were randomly allocated to three groups (extension, flexion, and neutral groups), and were injected with 5 mL of contrast when the neck was extended, flexed, or in the neutral position. Extent of contrast spread was determined by counting the number of vertebral body units (VBUs) through lateral epidurography.
  
  
  RESULTS
  Forty-two patients were equally allocated to the three groups. Radiographic spreads in the cephalad direction (median) was 1.0, 5.5, and 1.5 VBUs in the extension, flexion, and neutral groups, and spread was greater in the flexion than in the other two groups (P < 0.001). Median radiographic caudal spread was 10.0, 10.0, and 7.0 VBUs in the extension, flexion, and neutral groups, respectively, which was not significantly different among groups (P = 0.145).
  
  
  CONCLUSIONS
  Cranial spread of contrast in the high thoracic epidural space is limited. However, neck flexion increases cranial spread. These results suggest that when TEA is high, the tip of the epidural catheter should be located at the upper part of the level to be blocked and that neck flexion may cause an unwanted cervical block.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Samsung Seoul Hospital, Samsung Medical Center, Seoul, Korea.
authors.forename: Chul Joong
authors.initials: CJ
authors.lastname: Lee
authors.forename: Yunseok
authors.initials: Y
authors.lastname: Jeon
authors.forename: Young Jin
authors.initials: YJ
authors.lastname: Lim
authors.forename: Jae Hyon
authors.initials: JH
authors.lastname: Bahk
authors.forename: Yong Chul
authors.initials: YC
authors.lastname: Kim
authors.forename: Sang Chul
authors.initials: SC
authors.lastname: Lee
authors.forename: Chong Sung
authors.initials: CS
authors.lastname: Kim
mesh_terms: D000328:Adult; D000368:Aged; D000767:Anesthesia, Epidural / Q000009:adverse effects / Q000379:methods; D003287:Contrast Media / Q000008:administration & dosage* / Q000032:analysis; D004824:Epidural Space / Q000000981:diagnostic imaging; D005119:Extravasation of Diagnostic and Therapeutic Materials / Q000150:complications / Q000175:diagnosis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009333:Neck; D011187:Posture; D011859:Radiography; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging
chemical_list: D003287:Contrast Media