Safety and accuracy of blind vs. ultrasound-guided dorsal retrobulbar nerve blocks in horses-A cadaveric study.

Abstract

There is limited knowledge regarding the safety and accuracy of ultrasound-guided retrobulbar nerve blocks in horses. The aim of this study was to compare these parameters between blind and ultrasound-guided injection techniques for the dorsal retrobulbar nerve block in horses. Equine cadaver heads were used to inject the retrobulbar space with contrast medium (CM). Injections were performed either blindly based on anatomic landmarks (blind group, n=44) or under ultrasonographic guidance (US-group, n=44), equally divided between an experienced and unexperienced operator. Needle position and distribution of CM were assessed with computed tomography imaging and evaluated by a board-certified veterinary diagnostic imager blinded to the technique. Safety and accuracy of both techniques were compared. Ocular penetration was observed in two cases (n=2/44) in the blind group but not in the US group (n=0/44). No intrathecal, intraneural, or intravascular injections were seen in either group. Safety was significantly improved in the US group (p=.026). There was no statistically significant difference between the groups regarding the accuracy of the injection. Excellent accuracy was achieved more often with the ultrasound-guided technique (n=11/22) than with the blind technique (n=7/22) when performed by the unexperienced operator, but this difference was not statistically significant. To prevent globe-threatening complications and improve the safety of the injection, we recommend using the ultrasound-guided injection technique for the dorsal retrobulbar nerve block.