epinephrine in nerve blocks
Veterinarians might need to numb a horse’s foot with a palmar digital nerve (PDN) block for reasons ranging from lameness diagnostics to standing surgical procedures. But blocks don’t last forever, and practitioners can run into problems when working rapidly to try to finish up before the horse regains feeling in the area

Physicians sometimes add small amounts of epinephrine to local anesthetic solutions to intensify and prolong their analgesic effects. So Ana Velloso Alvarez, LV, a resident at the Auburn University College of Veterinary Medicine, in Alabama, and colleagues sought to test the approach in horses. She presented their results at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.

The researchers tested three anesthetic combinations in PDN blocks on lame limbs in six horses:

  • 2% lidocaine (a common local anesthetic choice for veterinarians performing nerve blocks);
  • 1% lidocaine; and
  • 1% lidocaine plus epinephrine.

Then, the team used the Lameness Locator (a tool designed to objectively measure lameness) to evaluate the horses’ gaits every five minutes for the first 30 minutes after PDN administration, and every 15 minutes for another 1.5 hours. They also measured skin sensation between the horses’ heel bulbs using a force gauge.

Velloso Alvarez said the treatments’ effects were no different for the first 30 minutes. Same goes for the two lidocaine-only treated groups for the longer duration; however, horses treated with lidocaine and epinephrine remained sound for significantly longer.

The team noted normal skin sensation in the groups that did not receive epinephrine, even though lameness had improved, Velloso Alvarez said. When the team used the epinephrine combination, however, the horses had decreased skin sensation.

Finally, she said, epinephrine did not cause any changes in horses’ heart rates or any skin reactions at administration sites.

Velloso Alvarez said it isn’t yet clear how long the epinephrine prolongs analgesia, and more research is needed to compare the combination’s effects to those of other local anesthetics.

Still, “because the combination of lidocaine and epinephrine increased the duration and potency of a PDN block, it may have beneficial applications for lameness examinations and standing surgery,” she said.