title: Spreading pattern of contrast medium in the high thoracic epidural space in rabbits: the effect of neck flexion and extension.
abstract: BACKGROUND
  Neck flexion has been shown to increase cranial spread of contrast agent when a small fixed volume was injected into the high thoracic epidural space. The purpose of this study was to evaluate the effect of volume of contrast medium on its distribution through the high thoracic epidural space during neck extension and flexion using the rabbit model.
  
  
  METHODS
  An epidural catheter was introduced into the epidural space of New Zealand white rabbits with the tip located at the T3-4 intervertebral level. The neck was extended or flexed (n = 8 for each group), and the contrast medium was injected with the volume increasing by increments of 0.1 ml/kg, up to 0.3 ml/kg. The spread of contrast medium was determined by counting the number of vertebral body units using lateral epidurographic images.
  
  
  RESULTS
  In both groups, the total spread of contrast medium was similar, increasing continuously with injected volume. The cranial spread was greater in the flexion group than the extension group. However, the caudal spread was greater in the extension than in the flexion group. In the extension group, the contrast medium spread caudally about twice as far as it spread cranially, but there was no statistically significant difference between cranial and caudal spread in the flexion group.
  
  
  CONCLUSIONS
  In the high thoracic epidural space of rabbit, the contrast medium of varying doses showed limited cranial spread. The flexion of the neck increased cranial spread and extension of the neck increased caudal spread.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Seoul National University Hospital, Seoul, Korea.
authors.forename: Mi-Hyun
authors.initials: MH
authors.lastname: Kim
authors.forename: Young Jin
authors.initials: YJ
authors.lastname: Lim
authors.forename: Deok-Man
authors.initials: DM
authors.lastname: Hong
authors.forename: Yun-Seok
authors.initials: YS
authors.lastname: Jeon
authors.forename: Hee Pyoung
authors.initials: HP
authors.lastname: Park
authors.forename: Young-Tae
authors.initials: YT
authors.lastname: Jeon
authors.forename: Soon Young
authors.initials: SY
authors.lastname: Shin
authors.forename: Sun Sook
authors.initials: SS
authors.lastname: Han