Retrobulbar and peribulbar regional anaesthesia techniques in rabbits: a cadaver study

OBJECTIVE: To describe and compare a retrobulbar (RBA) and two peribulbar (PBA-1 and PBA-2) injection techniques in rabbit cadavers. STUDY DESIGN: Prospective experimental cadaveric study. ANIMALS: A total of 30 New Zealand White Rabbit cadavers. METHODS: Computed tomography (CT) was performed to evaluate the needle position and the distribution of contrast agent. A total of 60 retrobulbar spaces underwent one of the three techniques (20 each) with a mixture of 1:2:2 iodinated contrast medium, methylene blue, and 0.9% saline solution with 0.7 mL for RBA, 1 mL for ventrolateral PBA-1 and 1 mL twice for dorsomedial and ventrolateral PBA-2. Intra-versus extraconal contrast distribution were compared. p < 0.05. RESULTS: In 13/20 RBA cases, the contrast distribution was intra- and extraconal, in 6/20 purely extraconal, and in 1/20 intraocular (into the globe). RBA showed a statistically significant extraconal distribution (p < 0.001). In group PBA-1, intra- and extraconal contrast distribution were present in 7/20 orbits, in 11/20 extraconal, and in 2/20 intraocular. There was a statistically significant extraconal distribution in the PBA-1 (p < 0.001). PBA-2 showed a mixed intra- and extraconal contrast accumulation in 7/20 orbits, extraconal in 5/20, and intraocular in 8/20. The dorsally placed needle resulted in a statistically significant intraocular location compared with the ventral needle. The injection resulted in a change in the needle position in one orbit in the PBA-2 group compared with the pre-injection scan. In all other cases with an intraocular contrast distribution, no change in needle position could be detected. CONCLUSION AND CLINICAL RELEVANCE: The lowest number of complications (intraocular contrast accumulation) was with RBA, but there was no pure intraconal distribution of contrast medium. This technique may be suitable if extraconal anesthesia is desired. Due to the high intraocular distribution, PBA-2 does not appear to be a suitable technique.