Eliminating the effect of epidural fat during dorsolumbar epidural analgesia in cattle

To compare the distribution of new methylene blue (NMB) solution injected into either the subperiosteal space or under the epidural fat at the first and second lumbar vertebral interspace in cattle.

Prospective experimental study.

Nine nonpregnant cows.

Needles were advanced towards the first interlumbar epidural space using a dorsal mid-line approach. Upon confirmation of successful penetration of the ligamentum flavum, group 1 received 5 mL of 0.12% NMB in 0.9% saline. In group 2, the needle was slowly advanced a further 7-10 mm to ensure injection under the epidural fat; the same dose was injected. The extent of cranial and caudal migration of dye, as indicated by staining of epidural fat and the dura mater was measured.

In group 1 (n = 4), NMB solution migrated only between the periosteum and the epidural fat. There was unilateral distribution in two cows. In contrast, there was no difference between left- and right-sided distribution in group 2 (n = 5), and the NMB solution migrated only between epidural fat and the dura mater. Although the dura mater was not penetrated in any animal of group 2, the dorsal roots were slightly stained and the overlying dura mater was heavily stained in these animals.

Variation in distribution of local anaesthetic solution can probably be overcome by deeper needle penetration of the epidural fat.