Ultrasound-guided versus blind intercostal nerve injection in equine cadavers

To describe the detailed anatomy of the equine thoracoabdominal region and to compare the accuracy of ultrasound-guided versus blind intercostal nerve injection techniques, targeting the thoracic intercostal nerves (T12-T18) in equine cadavers.

Randomized, blinded, cadaveric study.

Eight fresh adult equine cadavers.

Eight horse cadavers were used: one in phase I (436 kg; 4 years old) for anatomic landmarks identification and seven in phase II [420 (317-560 kg); 16 (3-22 years old) [median (minimum-maximum)] for comparative study. In phase I, dissections were performed to map muscular landmarks and intercostal nerve courses. In phase II, intercostal nerve injections were performed bilaterally using 3 mL of 0.05% methylene blue per site, with one hemithorax randomized to ultrasound-guided injection (49 repetitions) and the contralateral side to blind technique (49 repetitions). Gross dissections assessed nerve staining, pleural punctures and incorrect intramuscular injections. Statistical analyses included Shapiro-Wilk test for normality and McNemar test.

Success in nerve staining was higher with ultrasound-guided (41/49, 83.7%) than blind injections (25/49, 51.0%; p = 0.001). Pleural puncture was identified in ultrasound-guided (3/49, 6.1%) and blind approaches (7/49, 14.3%). Intramuscular dye deposition occurred in 8/49 (16.3%) of ultrasound-guided and 14/49 (28.6%) of blind injections. The costoabdominalis nerve (T18) exhibited the greatest disparity between techniques, with no nerve staining occurring with the blind approach and in 3/7 (42.6%) injections under ultrasound guidance. Gross dissection confirmed anatomical deviation of the T18 nerve, traveling approximately 2.4 ± 1.2 cm ventrocaudally, differing from cranial intercostal nerves.

Ultrasound guidance significantly improved the accuracy of intercostal nerve injections in horse cadavers. Detailed anatomical knowledge of the thoracoabdominal region, particularly of T18, is critical for optimizing regional anesthesia techniques in horses.