Ultrasound-Guided Lateral Transversus Abdominis Plane (TAP) Block in Rabbits: A Cadaveric Study

SIMPLE SUMMARY: Small rodents and, in particular, rabbits require special attention during anaesthesia since they develop a high level of stress following painful procedures or manipulations. The transversus abdominis plane (TAP) block is a locoregional technique that has been shown to provide good perioperative analgesia for abdominal surgery, reducing the stress during recovery from anaesthesia and the need for systemic analgesic drugs. The aim of this cadaveric study was to describe a US-guided lateral TAP block technique in rabbits and evaluate the spread of the dye administered by a single injection. Our results showed that this US-guided block is applicable and easy to perform in rabbits. However, a single injection of local anaesthetic may fail to cover the sensory component of the entire abdomen. It would be interesting to evaluate the same technique in vivo but using a double injection point, as recently described in other species. ABSTRACT: The aims of the study were to describe the ultrasonographic-guided lateral TAP block in rabbit cadavers and evaluate the spread of a lidocaine/methylene blue solution through a single fascial infiltration. The US-guided block and anatomical dissections were performed in 17 New Zealand rabbit cadavers. The probe was placed perpendicular to the column, one centimetre ventrally to the transverse processes, halfway between the iliac crest and the costal margin. External oblique (EO), internal oblique (IO), and transversus abdominis (TA) muscles were visualised, and 1 mL/kg of lidocaine 2% plus methylene blue 1% was injected. After dissection, the branches of spinal nerves stained were measured. Moreover, the percentage of length and height of the area marked were calculated. A good visualisation of the TAP was obtained in all 34 hemiabdomens. T11 nerve eminence was successfully stained in 52% of cases. T12, L1, and L2 were stained in 75%, 95%, and 100% of cases, respectively. L3 and L4 were stained in 60% and 40% of cases, respectively. The lateral TAP block with a single point of injection can be easily performed in rabbits, but it is not sufficient to cover the nerve eminences of the cranial abdomen. The two-point TAP block (lateral and subcostal) could represent a better option, particularly when large surgical incisions are required.