Many veterinarians keep tight clinical schedules, and waiting for nerve blocks (localized analgesia) to take effect during lameness exams can eat up valuable time. But a research team focused on diagnostic analgesia has good news: They recently found a way to help speed up analgesia onset to keep lameness exams moving.
Lindsey Boone, DVM, PhD. Dipl. ACVS, an assistant clinical professor of equine surgery and sports medicine at Auburn University’s College of Veterinary Medicine, in Alabama, presented her team’s findings at the 2018 American Association of Equine Practitioners Convention, held Dec. 1-5 in San Francisco, California.
Nerve blocks help veterinarians sleuth out areas of pain in the foot and/or leg by numbing potentially painful structures in a methodical way, starting low and moving up the limb. If a lameness lessens after a block, that gives the veterinarian clues as to which parts of the foot or leg are likely involved.
Most of the local anesthetics veterinarians use in horses have low (an acidic) pH but high ionization constants—the discrepancy between the two can slow a drug’s delivery to the nerves. Boone’s team wondered if increasing the pH of the anesthetics with a buffering solution (sodium bicarbonate, in this case) to lessen the discrepancy could help the drug reach the target nerves more rapidly.
The researchers measured the pH of a common unbuffered local anesthetic drug and a buffered solution of the same drug prior to testing them on nine unsound horses. The researchers objectively measured the horses’ gaits using a Lameness Locator (a device designed to objectively quantify lameness) prior to the block as a baseline, as well as every five minutes following the block for 60 minutes.
Results showed the buffered solution alleviated lameness in 10 minutes, while the unbuffered block took twice as long. The horses treated with the buffered treatment also stayed sound longer.