Epidural anesthesia and analgesia are used in dogs for a number of reasons. They can provide anesthesia of caudally located dermatomes and analgesia that extends to the forelimbs.1,2 The epidural space is located between the vertebral column and the dura mater. The technique of epidural injection in dogs is almost invariably performed at the lumbosacral epidural space, although, in larger dogs, it may occasionally be performed at the sacrococcygeal epidural space.1-3 Some factors that influence the cranial migration of material injected into the epidural space include injectate volume, rate of infusion, patency of intervertebral foramina, posture, gravity, baricity, and vascular absorption.4 The volume of epidural injectate required to reach a specific spinal cord level on the basis of body length has been evaluated in pigs and dogs by use of radio-opaque solutions and dermatome analgesia.5,6 The discovery of spinal opioid receptors spawned the practice of providing analgesia by epidural administration of opioids. Small amounts provide substantial analgesia with minimal systemic effects.7
It has been recommended that animals be positioned in sternal recumbency and kept in that position following injection to provide bilateral analgesia or in lateral recumbency with the surgical site as the dependent side until the block has taken effect.7 To our knowledge, no studies exist that support the effects of positioning on the distribution of epidurally injected material in dogs. The purpose of the study reported here was to determine whether the body position during recumbency has an effect on cranial migration of epidurally administered methylene blue in cadavers of clinically normal dogs.
Body condition score
Methylene blue injection USP, Taylor Pharmaceuticals, Decatur, Ill.
Monoject Sensi-Touch spinal needle, Sherwood Medica, St Louis, Mo.
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