Comparison of three regional anaesthetic techniques for infraorbital or maxillary nerve block in cats: a cadaveric study

Objectives The maxillary nerve courses very close to the globe, rendering cats - with their large eyes - at risk of globe penetration during infraorbital or maxillary nerve blocks. Therefore, the goals of the study were to compare the distribution and potential complications of three infraorbital or maxillary regional injection techniques. Methods Twenty-three bilateral maxillae of cat cadavers were used in a randomised blinded trial. Each maxilla was injected with a 0.2 ml 1:1 mixture of lidocaine 2% and a contrast medium by one of three injection techniques: infraorbital foramen (IOF; n = 14); infraorbital canal (IOC; n = 16); or maxillary foramen (MF; transpalpebral approach; n = 16) using a 25 G 1.6 cm needle. CT imaging of each cadaver head was performed before and after injections. A radiologist scored injectate distribution (none [0], mild [1], moderate [2], large [3]) in four locations: rostral, central and caudal IOC, and at the MF, for which the distribution side was also determined. Comparisons were performed with ordinal logistic mixed effects (P <0.05). Results The median (range) total distribution score of the IOC and MF technique were significantly higher compared with the IOF technique (6.5 [4-12], 4 [2-8] and 0 [0-10], respectively). The total IOC score was also significantly higher compared with the MF technique. Injectate distribution at the MF was significantly more central following IOC injection compared with MF injection, which distributed centrolaterally. None of the techniques resulted in intraocular injection. Conclusions and relevance The IOC and MF techniques produced a satisfactory spread of the mixture that could result in effective maxillary anaesthesia in cats. Further studies are required to determine the effectiveness and safety of these techniques.