Noor: “An incredible learning experience”

Noor. Photo courtesy of Syed Abidi.

Veterinary surgeons weren’t the only WCVM specialists faced with “firsts” during the procedure on Noor, the Arab mare with a cancerous growth on her jaw. The veterinary college’s anesthesiology team also had the chance to break new ground during the horse’s lengthy surgery.

“I learned that you can anesthetize a horse for 13 hours and everything can go well which I wouldn’t have believed before,” says Dr. Perrine Benmansour, an anesthesiology resident at the veterinary college.

She and her supervisor, anesthesiologist Dr. Tanya Duke, worked alongside the surgical team during the round-the-clock procedure. As Benmansour explains, Noor’s surgery was ideal for her and Duke to try various things including remifentanil — an opioid that’s a powerful analgesic (pain relieving) drug.

Besides its potency, remifentanil is the only opioid that’s not metabolized by the liver. Another advantage: it’s a short-acting drug that takes only a few minutes to disappear from a patient’s blood system — making it easier for anesthesiologists to control intake and to swiftly make changes if an emergency arises.

While remifentanil is widely used as a surgical analgesic in small animals, no one has tested its use in horses. “There have been many published studies showing that it’s a good analgesic for dogs and cats — but there were no studies involving horses,” explains Benmansour, who investigated remifentanil in May 2010 with Duke, Dr. Joe Bracamonte and veterinary student Michelle Graham.

The project, which was supported by the Equine Health Research Fund, is part of Benmansour’s Master of Veterinary Science (MVetSc) degree program. During the cross over study, Benmansour and Duke anesthetized six healthy horses at three separate times using three different anesthesia infusion treatments.

The project compared remifentanil combined with dexmedetomidine (an alpha 2 agonist drug with analgesic properties) with the standard combination of morphine and dexmedetomidine. Duke and Benmansour also used a third treatment of dexmedetomidine and saline as the study’s control.

“To mimic clinical experiences, we added in dexmedetomidine because it’s widely used in combination with morphine. It provides better analgesia and a better level of anesthesia,” points out Benmansour.

During each hour-long treatment, researchers recorded a range of measurements including blood pressure, heart rate, core body temperature, blood gases and cardiac output. After analyzing all of their data, the research team found no statistically significant difference between any of the three treatments.

However, Benmansour does flag one difference witnessed during the remifentanil treatments: “It wasn’t statistically significant, but about 30 minutes into the procedure, we did see a big drop in the amount of isoflurane (inhalant agent) needed to maintain a light surgical plane in patients. If remifentanil allows you to use less isoflurane, it would make it much easier to manage anesthesia with fewer side effects,” says the resident, who presented an abstract and an oral presentation of her research at the Association of Veterinary Anesthetists’ biannual meeting in Italy this spring.

Backed by their study’s results, Benmansour and Duke both felt confident enough in suggesting the use of remifentanil for Noor’s surgery. The opioid is about six times more expensive than morphine, but in Noor’s case, the anesthesiologists both believed that remifentanil’s power as an analgesic and its short-acting capability were worth the cost.

“Thirteen hours under anesthesia is a long time for a horse — especially since horses are already trickier to anesthetize because of their size. But actually, Noor recovered very well,” says Benmansour. She adds that in comparison to the study, they used only half the amount of remifentanil (three milligrams per kilogram per hour) for Noor without any major effects.

“Noor did show some of the problems that we expect during any anesthetized procedure — cardiovascular and respiratory depression — but she responded very well to treatment,” says Benmansour. Noor was able to stand up less than 90 minutes after her surgery and only experienced some temporary wobbliness — a side effect from another opioid called buprenorphine.

Overall, Noor’s case was an incredible learning experience that Benmansour plans to record in a case report. But although the surgery demonstrated the effectiveness of remifentanil in a clinical setting, the resident cautions that larger investigations need to be done before the opioid can be considered as a regular analgesic option for equine surgeries.

For example, researchers need to test different infusion rates to see if there are more significant effects from the drug. Plus, the opioid needs to be tested in different surgical simulations to gauge its pain relieving properties.

But for Benmansour, it was still a thrill to use remifentanil in a clinical case and — based on her study’s findings — be confident about the outcome: “I really thought in my heart that it was the best for her — and I’m glad that it worked out.”