Effects of approach and injection volume on diffusion of mepivacaine hydrochloride during local analgesia of the deep branch of the lateral plantar nerve in horses.

This research examined how the method of injection and the volume of injection can affect the diffusion of the anesthetic mepivacaine hydrochloride during local anesthesia of the deep branch of the lateral plantar nerve in horses.

Study Methodology

• This experimental study involved 16 adult horses.
• They received either 2 mL (low volume) or 8 mL (high volume) of a 50:50 mixture of mepivacaine hydrochloride and iohexol. This was injected in one of two ways to numb the deep branch of the lateral plantar nerve (DBLPN).
• The first technique involves an insertion of a needle 15 mm distal to the head of the fourth metatarsal bone and directed it perpendicular to the limb.
• The second technique involved inserting a needle 20 mm distal to the head of the fourth metatarsal bone, directing it in a proximodorsal direction.
• Lateromedial radiographs were taken before and at 5, 15, 30, and 60 minutes after injection.
• These radiographs were analyzed to measure how far the contrast solution, standing for the anesthetic, diffused, and whether any contrast agent appeared in the tarsal sheath or tarsometatarsal joint.

Study Results

• There were high levels of variability in how far the contrast solution diffused among injections.
• High-volume injections spread significantly further in both directions than low-volume ones.
• In 16% of injections, the contrast agent was found within the tarsal sheath, and in 6%, it appeared within the tarsometatarsal joint.
• No significant variation was found in the risk of accidental injection into the tarsal sheath or tarsometatarsal joint between the two methods and volumes of anesthetic used.
• Mepivacaine diffused significantly further distally with the first technique than with the second, but diffused significantly further proximally with the second technique than with the first.
• For both techniques, the diffusion in the distal direction significantly increased over time, but not in the proximal direction.

Conclusions

• The diffusion of the mepivacaine-iohexol solution demonstrated considerable variability after either DBLPN nerve block technique.