Anesthesia case of the month. Can an epidural block still be performed in this dog?

Computer tomographic comparison of cranial spread of contrast in lumbosacral and sacrococcygeal epidural injections in dog cadavers

OBJECTIVE

To compare the cranial spread of epidural injectates between lumbosacral (LS) and sacrococcygeal (SCo) approaches in order to guide volume selection for SCo epidural anaesthesia in the dog.

STUDY DESIGN

Prospective, randomized cadaveric experimental study.

ANIMAL

A group of 13 adult greyhound cadavers.

METHODS

The greyhound cadavers were randomly allocated to receive an epidural injection of diluted contrast via the LS or SCo approach. Incremental volumes (0.1, 0.2, 0.4 and 0.6 mL kg^-1) were injected consecutively, and a computed tomography (CT) scan was completed following every volume increment. Cranial spread of contrast was recorded by counting the number of vertebrae cranial to the LS space that the injectate had reached, expressed as a vertebral value (n). This vertebral value was measured taking into consideration the percentage of the cord surrounded by contrast (vertebral canal coverage, %).

RESULTS

The cranial spread of contrast was similar at 0.1 mL kg^-1 [1 (0-3) versus 2 (1-3) n], 0.2 mL kg^-1 [3 (0-10) versus 3 (1-5) n], 0.4 mL kg^-1 [12 (9-18) versus 11 (3-19) n] and 0.6 mL kg^-1 [18 (12-20) versus 15 (10-23) n] for the LS and SCo injections, respectively (p = 0.945). There was a significant interaction between the volume injected and vertebral canal coverage (p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

The cranial spread of contrast was similar, independent of whether the epidural injection was performed in the LS or SCo intervertebral space. Current volume guidelines used for the LS approach may produce similar distribution patterns when the SCo approach is used. Further studies are required in order to evaluate the in vivo effectiveness and the adequacy in differently sized dogs of the results found herein.