Ultrasound-guided thoracic paravertebral block: cadaveric study in foxes (Vulpes vulpes)

To describe an ultrasound-guided thoracic paravertebral block in canidae.

Prospective, experimental, cadaveric study.

Twelve thawed fox cadavers.

A 15 MHz linear transducer was used to visualize the paravertebral space at the level of the fifth thoracic vertebrae. Iohexol (300 mg mL^-1) at 0.2 mL kg^-1 was injected into the right and left paravertebral spaces under ultrasound guidance using a Tuohy needle. The needle was advanced in a lateral to medial direction using an in-plane technique. Injections were performed by two operators, each performing 12 injections in six fox cadavers. A thoracic computed tomography was then performed and evaluated by a single operator. The following features were recorded: paravertebral contrast location (yes/no), length of contrast column (number of intercostal spaces), location of contrast relative to the fifth thoracic vertebrae (cranial/caudal/mixed), epidural contrast contamination (yes/no), pleural contrast contamination (yes/no) and mediastinal contrast contamination (yes/no).

All injections resulted in paravertebral contrast distribution (24/24). The mean length of the contrast column was five intercostal spaces. Contrast spread was caudal to the injection site in 54% (7/24), cranial in 29% (4/24) and mixed in 17% (3/24). Pleural contamination was observed in 50% (12/24) of injections; 42% (10/24) and 4% (1/24) of the injections resulted in mediastinal and epidural contamination, respectively.

Injection of the paravertebral space in canidae is possible using the technique described. Possible complications include epidural, pleural and mediastinal contamination. To establish clinical efficacy and safety of this technique, further studies are required.