Ultrasound-guided external oblique intercostal block technique in rabbits ( Oryctolagus cuniculus ): a cadaveric study

Background: Locoregional anesthesia is an essential component of multimodal analgesic and anesthetic techniques. However, few are described in rabbits, especially those aimed at the cranial abdominal wall. The aim of this study was to describe the external oblique intercostal (EOI) block technique in rabbits and compare the spread of two injectate volumes across the paracostal region and cranial abdominal wall. Methods: Eight rabbit cadavers (16 hemithoraces) were randomized to receive ultrasound-guided injections between the external abdominal oblique and external intercostal muscles. Each rabbit received 0.25 mL/kg (LV) and 0.5 mL/kg (HV) of 1% new methylene blue with immediate tissue dissection. Site of needle insertion, spread of injectate, and number of stained intercostal spaces and nerves were assessed by a blinded investigator. Results: Injection points ranged from intercostal spaces 5-12. There were no differences between HV and LV groups in the number of covered intercostal spaces or dorsal, caudal, and total (cranial + caudal) spread. There was significantly more ventral and cranial spread in the HV group as well as staining of intercostal nerves. Conclusions and Clinical Relevance: Injection within the EOI fascial plane successfully stained intercostal nerves associated with the thoracic wall and cranial abdomen; higher volumes provided significantly more spread in the cranial and ventral directions and stained more intercostal nerves. While the EOI block using a volume of 0.5 mL/kg could be a technique used to provide regional anesthesia of the rabbit paracostal region and cranial abdomen, future studies would be needed to determine clinical safety and efficacy.