Comparing blind and ultrasound-guided retrobulbar nerve blocks in equine cadavers: the training effect.

Twenty-two equine cadavers were divided into three groups: blind RNBs were performed bilaterally in eight cadavers, US-guided RNBs were performed in seven cadavers bi-laterally, and again blind RNBs were performed in seven cadavers bilaterally after US-guided training. All RNBs were performed by the same two inexperienced operators and a combination of contrast medium (CM; 1.25ml) and methylene blue dye (1.25ml) were injected.

Needle posi-tioning in the periorbita and the distance of CM to the optic foramen were assessed using com-puterized tomography (CT). Dye spreading was evaluated dissection. In group 1, 37.5% of the in-jections were in the optimal central position in the periorbita; in group 2, 69.2% and in group 3, 71.4%, showing a trend towards significance between groups 1 and 2 (p= 0.056) and groups 1 and 3 (p=0.069).

The mean CM distribution distance was not significantly different between all groups. Group 1 had 18.75% intraocular injections versus 0% and 7.1% in group 2 and group 3 (not significant). US-guidance did not show significant increases in accuracy or decreases in complications.

However, the effects on accuracy showed a trend towards significant improve-ment and larger scale follow-up studies could show significant training effects of US-guidance.