Spreading pattern of epidurally administered contrast medium in rabbits

Background: The aim of this study was to examine the precise spreading pattern of epidurally administered contrast medium with small increments of injection volume for determining both the exact volume of the dose required and the site of epidural injection according to different target segments of the spinal cord in a rabbit epidural model. Method: Following pentobarbital anesthesia, the epidural puncture was done surgically with a round-tipped blunt hook. The tip of the epidural catheter was located at either the mid-portion of T7 (T7 group, n=7) or T12 (T12 group, n=8). Injection of the contrast medium was started at 0.1 ml/kg and increased by 0.1 ml/kg up to a maximum of 0.6 ml/kg. Results: In both groups, the extent of spread increased continuously with increasing injected volume (T7 group: r(2)=0.91, P= 0.0001; T12 group: r(2)=0.86, P=0.0001) and the total spread of contrast medium was similar. However, the spread was not Linearly volume dependent. The total number of segments (y) through which the contrast medium spread during changes in its volume (x) in the T7 and T12 groups was calculated as y=4.0+41.8.x-28.1x(2) and y=0.2+57.7x-43.5x(2). respectively. The contrast medium spread in both rest al and caudal directions, equally from the catheter tip in the T7 group, whereas it spread rostrally about twice as far as it spread caudally in the T12 group (P<0.05). Conclusion: In rabbits, it is recommended that at the lower thoracic or lumbar segments the tip of the epidural catheter should be located 1-3 segments below the target segment because of more rostral spread. In the case of mid-thoracic segments, however, placement at the target segment is recommended. In addition, a small titration of volume to achieve a particular range of epidural spread should be required.