Description of an ultrasound-guided rectus sheath block injection technique and the spread of dye in calf cadavers.

Objectives: To describe an ultrasound-guided rectus sheath (RS) block technique in calves with injections of methylene blue and assess the extent of injectate spread and nerve staining in calf cadavers.

Study Design: Prospective, experimental, blinded cadaveric study.

Animals: A total of 16 calf cadavers weighing 30.7 ± 7.1 kg.

Methods: Using an ultrasound-guided, in-plane technique, each cadaver was injected with both a low (LV; 0.25 mL kg) and high (HV; 0.5 mL kg) volume of methylene blue dye. Volumes were randomly assigned to the left or right hemiabdomen. Ultrasound imaging was scored based on landmarks and needle visualization, and duration to perform injections were assessed. Dissections were performed immediately after injections. Staining of ventral branches of spinal nerves and the extent of dye spread were recorded by an anatomist unaware of treatment allocation.

Results: The number of nerves stained in treatments LV and HV were 2.3 ± 1.7 and 4.4 ± 1.3, respectively (p = 0.0001). Branches of thoracic nerves T7-13 and lumbar nerves L1-2 were completely stained 6.3%, 6.3%, 31.3%, 62.5%, 56.3%, 37.5%, 31.3%, 6.3% and 0%, respectively, in treatment LV and 0%, 12.5%, 50%, 93.8%, 100%, 93.8%, 62.5%, 25% and 6.3%, respectively, in treatment HV. Ultrasound imaging was scored excellent in most cadavers and needle visualization deemed excellent in all injections. The mean duration to perform RS injections in both treatments was 2 (range, 1-6) minutes.

Conclusions And Clinical Relevance: Nerve staining results from treatment HV suggest that this RS injection technique could be clinically useful in ventral midline surgical procedures, including umbilical procedures, in calves. This study supports future clinical trials in calves.