Ultrasound-guided versus blind intercostal nerve injection in equine cadavers.

Overview

• This study compared the accuracy of ultrasound-guided versus blind injection techniques for targeting thoracic intercostal nerves in horse cadavers.
• Ultrasound guidance significantly improved the precision of nerve injections compared to the traditional blind method.

Study Purpose and Background

• The research aimed to describe the detailed anatomy of the equine thoracoabdominal region related to the thoracic intercostal nerves (T12-T18).
• The study also sought to compare two different injection techniques used for regional anesthesia: ultrasound-guided injections versus blind (landmark-based) injections.
• Accurate nerve blocks are essential in equine medicine for pain management, but challenges exist due to anatomical variations and risk of complications such as pleural puncture.

Methods

• Eight fresh adult horse cadavers were used in two phases:
• Phase I: One horse cadaver (4 years old, 436 kg) underwent detailed anatomical dissection to identify muscular landmarks and the course of intercostal nerves.
• Phase II: Seven horse cadavers with varying weights (317–560 kg) and ages (3–22 years) were used to conduct the comparative injection study.
• In Phase II, both sides of each cadaver’s thorax were injected:
• One hemithorax was assigned to ultrasound-guided injections (49 injections total).
• The opposite hemithorax received blind injections (49 injections total).
• Each injection site received 3 mL of 0.05% methylene blue dye to visualize spread around nerves.
• Post-injection, gross dissection assessed:
• Whether the nerve was effectively stained/targeted.
• Occurrence of pleural punctures (which are possible complications).
• Incorrect intramuscular injections where dye was deposited into muscle rather than around nerve.
• Statistical analysis included tests for normality and comparing paired proportions for success rates using McNemar test.

Results

• The ultrasound-guided technique had a significantly higher success rate of nerve staining at 83.7% (41/49 injections) compared to 51.0% (25/49 injections) for the blind technique (p = 0.001).
• Pleural punctures occurred less frequently in ultrasound-guided injections (6.1%) than blind injections (14.3%), though both had some incidence.
• Intramuscular dye deposition was less common with ultrasound-guided injections (16.3%) than blind injections (28.6%), indicating better precision of needle placement.
• The T18 nerve, known as the costoabdominalis nerve, showed the largest difference in success rates:
• Blind injections failed to stain the T18 nerve in any case.
• Ultrasound-guided injections achieved nerve staining in approximately 42.6% (3/7) of cases.
• Anatomical dissection revealed that the T18 nerve travels ventrocaudally about 2.4 ± 1.2 cm from the intercostal space, deviating from the path of more cranial intercostal nerves, which may explain the difficulty of blind injections at this site.

Conclusions and Implications

• The study demonstrated that using ultrasound guidance significantly improves the accuracy of intercostal nerve injections in horse cadavers.
• Blind injections are less reliable and pose higher risks of incorrect placement and potential complications.
• Detailed knowledge of equine thoracoabdominal anatomy, especially the unique course of T18, is critical for improving regional anesthetic approaches.
• These findings emphasize the value of ultrasound guidance in clinical settings to enhance safety and efficacy of nerve blocks for equine pain management.
• Future applications may include improved protocols and training for ultrasound use to optimize outcomes in equine veterinary practice.