Abstract
Background
This prospective pilot cadaveric study aimed to develop an ultrasound-guided transversus abdominis plane (TAP) block technique that desensitizes cranial and mid-abdominal wall in pigs.
Methods
In phase I, the ultrasound anatomy of the abdominal wall musculature was examined on three pig cadavers and the ultrasound localization of the needle in the corresponding interfascial plane was practised. In phase II, a three-point TAP injection was performed in three freshly euthanized cadavers. A 1% methylene blue solution (0.3 mL/kg per injection point) was injected between the transversus abdominis and internal oblique muscle. In phase III, methylene blue solution was injected at four points (0.2 mL/kg per injection point) in four anaesthetized pigs prior to euthanasia. Positive nerve staining was defined as continuous staining of at least 1 cm of the nerve length. Binary variables (positive/negative) were used for nerve staining assessment.
Results
The four-point technique with a lower injected volume stained more nerves than the three-point technique with a higher injected volume. In phase III, 69% of the observed nerves from the eighth-last thoracic to the third lumbar nerve were stained. The nerves in the centre were stained with a higher success rate, while the eighth-last thoracic and the second lumbar nerve were stained with less success (1/8 and 3/8, respectively). The third lumbar nerve was not reached by any injection.
Conclusions
The four-point TAP technique could be used as part of a multimodal analgesia approach for cranial and middle abdominal surgery in pigs, but live animal studies are needed to evaluate the clinical applicability and efficacy of desensitisation.