Technical note on cervical epidural catheterization in two adult horses: Injectate distribution and epidural space effects.

Overview

• This study investigated how a contrast solution spreads within the epidural space when administered via a cervical epidural catheter in adult horses and examined the tissue effects of leaving the catheter in place for up to 17 days.

Study Purpose

• To determine how far down the spine (caudally) a contrast agent can diffuse when injected through a cervical epidural catheter (CEC).
• To describe any pathological changes in the epidural space following the prolonged presence of an indwelling CEC in horses.

Methodology

• Subjects: Two mature adult horses were used in this pilot study.
• Catheter placement: Cervical epidural catheters were inserted under ultrasound guidance to ensure accurate positioning in the epidural space of the cervical spine.
• Contrast injections: Both horses were initially injected with 5 mL of a 50% Iohexol contrast solution, followed by radiographs to confirm catheter placement.
• A total of 15 mL of the contrast solution was injected in 5 mL aliquots every 5 minutes, up to 25 minutes post-initial injection.
• Imaging: Laterolateral radiographs (side views) were taken every 5 minutes after the initial injection in the caudal cervical region to track the spread of contrast material.
• Post-study examination: Both horses were euthanized 16 or 17 days after catheter placement, and the epidural regions around the catheters were examined through gross necropsy to evaluate pathological changes.

Key Findings

• In one horse, the contrast had reached the cranial part of the C6 vertebra 25 minutes after administration of a total 15 mL contrast volume.
• In the other horse, the contrast reached cranial C6 as early as 1 minute after only 5 mL had been injected.
• The maximum caudal spread of contrast solution seemed to plateau after 15 mL and between 20-25 minutes, indicating a limited diffusion extent beyond these points.
• Gross examination of the epidural space at 16-17 days post-catheter placement revealed mild inflammation and fibrosis around the catheter insertion sites.
• The observed tissue reactions were consistent with prior findings in horses that had sacrococcygeal or lumbosacral epidural catheters, indicating a similar safety profile irrespective of catheter location.

Conclusions and Implications

• A volume of 10-15 mL of contrast solution is sufficient to reach the upper portion of the brachial plexus in the caudal cervical region via a cervical epidural catheter.
• The presence of an indwelling cervical epidural catheter for up to 17 days results in mild, localized inflammatory and fibrotic changes, similar to those seen with epidural catheters in other spinal locations in horses.
• These findings suggest the feasibility of using cervical epidural catheters for targeted delivery of medication to the caudal cervical spine and brachial plexus region.
• The study recommends further research to evaluate the therapeutic effects and safety of treatments administered through cervical epidural catheters for conditions affecting the caudal cervical vertebrae in horses.