Similar performance between modified retrobulbar and ultrasound-guided Peterson nerve blocks using computed tomography in bovine cadavers.

Abstract

Objective: Description and performance of an ultrasound-guided Peterson (UP) block technique were compared to those of a conventional modified retrobulbar (RB) nerve block in bovine cadaver heads by use of CT.

Methods: This was an original descriptive study using 10 normal orbits from 5 bovid cadavers between April 17 and 23, 2024. Standardized techniques for the modified RB and UP blocks were utilized, with each technique randomly performed on either orbit of each head. Blocks were performed with 9-cm, 18-gauge spinal needles and iopamidol as a contrast solution. Ultrasound guidance involved the use of a 12-MHz linear transducer, and subsequent imaging of contrast distribution was performed with a GE Lightspeed 16-slice CT scanner.

Results: Contrast deposition within the intraconal space was observed in 5 of 5 RB blocks and 5 of 5 UP blocks. No extraconal contrast deposition was observed in either block technique. Extension of contrast in close association with the optic nerve to the level of orbital foramen was observed in 5 of 5 RB orbits and 5 of 5 UP orbits. Extension of the contrast to the level of the foramen orbitorotundum was seen in 5 of 5 RB orbits and 3 of 5 UP orbits. Correct needle placement was observed in 5 of 5 UP orbits and confirmed on CT images.

Conclusions: The RB and UP blocks performed similarly, demonstrating similar intraconal distribution of contrast medium and no inadvertent distribution to unintended anatomical locations.

Clinical relevance: The performance of the ultrasound-guided technique in live cattle and ability to successfully achieve adequate blockade need further study.