Ultrasound-guided retrobulbar nerve block in horses: a cadaveric study.

This study explored the efficacy and impact of the retrobulbar nerve block technique in horses by visualizing the anesthesia’s dispersal through ultrasound. The researchers tested three different volumes of contrast medium and noted that optimal needle placement within the retractor bulbi muscle cone led to effective dispersal of the medium towards the nerves exiting the orbital fissure.

Methods Used

• The research was under a prospective experimental cadaver study layout involving 20 equine cadavers.
• Ultrasound-guided retrobulbar injections were performed on 40 cadaver orbits.
• The ultrasound was used to visualize and score needle placement within the retractor bulbi muscle cone and the spread of the injected contrast medium (CM) towards the orbital fissure.
• A computerized tomography (CT) scan assessed needle position and CM destination, which was then compared to the success rate of the injections determined by the ultrasonic visualization.

Results Found

• The study found a clear correlation between higher scores for ultrasound visualization and a higher success rate for intraconal contrast medium injection as shown on the CT images.
• Successful intraconal needle placement resulted in the contrast medium reaching the orbital fissure every time.
• The contrast medium reached the orbital fissure in six orbits where the needle placement was outside the cone.
• While using different volumes of contrast medium i.e., 4, 8, and 12 mL, the orbital fissure was reached in 16, 23, and 28 out of 34 injections respectively.

Conclusion

• The study showcases the utility of ultrasound in visualizing the anatomical structures in the equine body and aiding the needle placement during retrobulbar injections.
• Despite the successful findings, the study suggests that the technique should undergo more controlled clinical trials to assess its practicability and effectiveness in a real-world clinical scenario.