Ultrasound-guided erector spinae plane block in horses: a cadaver study.

This research paper examines the effects of an ultrasound-guided erector spinae plane (ESP) block, a type of anesthesia used in managing pain, performed on fresh horse cadavers. Using a dye to track the effects, they found that it could be an effective method in alleviating pain related to structures affected by the dorsal rami of the thoracic spinal nerves, although there needs to be additional investigation regarding potential epidural complications.

Methodology

• To start the experiment, a group of 11 adult equine cadavers were used.
• One specific segment, the region around the sixteenth thoracic vertebra (Th16), from one of the cadavers was excised and underwent magnetic resonance imaging.
• On the remaining 10 horse cadavers, a solution consisting of 2% lidocaine (a local anesthetic) and dye was injected into the space between the transverse process of Th16 and the erector spinae muscles. The injection was guided using an ultrasound technique with a convex transducer.
• Post-injection, a dissection was immediately performed. Measurements were taken to establish the extent of dye distribution, and any presence of dye was examined in the thoracic and abdominal cavities, and the epidural space.
• A deeper dissection was conducted to ascertain if the dye had stained the dorsal and ventral rami of the spinal nerves and the sympathetic chain.

Results

• The analysis revealed that the thoracolumbar fascia (the connective tissue of the abdominal wall) was stained in 17 out of 20 injections, indicating that the injected solution had largely been distributed successfully. However, three injections ended intramusically, or within the muscles.
• The dorsal rami, a branch of the spinal nerves, showed multisegmental staining in the 14 injections where staining was evaluated.
• Ventral rami staining occurred in three of the 14 injections where staining was analyzed. This result suggests that the solution had reached this part of the spinal nerves less frequently.
• Dye migration to the epidural space was observed in four out of 20 (20%) injections, raising concerns over possible complications.
• There was no evidence of the dye present in the abdominal and thoracic cavities or on the sympathetic chain, showing that the injection largely stayed in the target area.

Conclusions

• The findings from this study suggest that ESP block could be a useful method in desensitizing the structures that the dorsal rami of the thoracic spinal nerves innervate. This application of the technique could prove beneficial in managing pain in horses treated with it.
• However, the researchers concluded that further investigation is necessary to evaluate potential complications, particularly related to the observed contamination of the epidural space by the solution.