by Jessica Eissfeldt
Surgical specialists use lidocaine as a local anesthetic during surgeries and as a nerve block in lameness tests, but can they rely on it for damage control after small intestinal colic surgery? A team of scientists at the Western College of Veterinary Medicine (WCVM) in Saskatoon, SK, is striving to answer that very question.
The prognosis for all types of colic surgery has dramatically improved in the past 20 years, but horses that undergo surgery for small intestinal colic still have only a 50-50 chance of survival.
The main problem that faces surgical specialists during small intestinal colic surgery is having enough healthy intestinal tissue left to repair the damage caused by colic, explains Dr. Ryan Shoemaker of WCVM. The surgical specialist and assistant professor adds that small intestinal-related surgeries are more expensive than other types of colic surgeries.
Besides trying to prevent further damage to the patient’s intestine during surgery, Shoemaker says surgeons need to determine what part of the intestine is healthy and safe to use and what part of the intestine is dead.
And, even if horses survive colic surgery, they still aren’t certain to recover. Post-operative complications such as ileus (partial or complete paralysis of the intestine) or intestinal adhesions (when the intestine abnormally attaches to itself or to other structures in the abdomen as a result of intestinal wall inflammation) can cause horses to colic once again – anywhere from seven days to six months after surgery.
“Horses that develop post-operative intestinal adhesions may experience recurrent colic that may require additional surgery to deal with the problem,” says Dr. Jenny Kelly, a large animal surgical resident at WCVM.
In some cases, adhesions forming after colic surgery can become so extensive that they can’t be corrected. Surgeons faced with this problem may be forced to euthanize a patient during surgery.
“Even if we get the horses happy and healthy and leaving the hospital, adhesions could affect them later, so it’s not cut and dry,” points out Kelly. “We always make sure that owners are aware of the potential for more problems.”
That’s where a WCVM research study on horses undergoing colic surgery comes into play. Supported by the Equine Health Research Fund, four scientists – Shoemaker and Kelly along with Drs. David Wilson and Andrew Allen – are determining whether intravenous (IV) administration of a drug called lidocaine can actually help to prevent intestinal adhesions after colic surgery.
Lidocaine is commonly used as a local anesthetic and as a nerve block in lameness tests. It reduces pain, acts as an anti-inflammatory agent, and also helps to maintain movement in a horse’s gut after colic surgery.
What’s intriguing about lidocaine is its potential ability to prevent neutrophil-related intestinal damage after colic surgery. Neutrophils are the primary white blood cells that appear and invade the damaged intestine, causing swelling, inflammation, and common complications like ileus and intestinal adhesions.
Other researchers have reported that IV administration of lidocaine has decreased the migration of neutrophils and reduced the white blood cells’ adverse effects on tissue in humans and other species.
“If we can keep the outside of a horse’s intestine from becoming invaded with neutrophils, it’s less likely that we’ll get adhesions and other complications associated with these problems,” says Shoemaker, the study’s lead investigator.
Specialists often use three other drugs when a horse undergoes colic surgery: flunixin meglumine, used as an anti-inflammatory agent and pain killer, and a combination of the broad-spectrum antibiotics gentamicin and penicillin. But because lidocaine is cheap, readily available at most surgical clinics, and has minimal side effects, Shoemaker says the research team wanted to test its ability as a neutrophil-blocker.
“If we can administer lidocaine and decrease inflammation, that’s the biggest benefit we’re hoping to achieve,” Shoemaker says.
As outlined in the study, two surgical teams have conducted experimental surgery in 12 horses during the past 12 months. For each horse, the surgeons recreated two common scenarios related to small intestinal colic: partial occlusion (obstruction) of the small intestine and a distended bowel.
Once the teams completed their surgical protocols in each horse, the patient received a saline solution intravenously (the control group) or an initial dose of lidocaine (1.3 milligrams per kilogram over five minutes) followed by a continuous flow of the drug at .05 mg per kg (per minute) over a two-hour period (the treatment group). To maintain the study’s impartiality, the surgical teams weren’t aware of what treatment was used on each horse.
Dr. Andrew Allen, a veterinary pathologist at WCVM, is in charge of evaluating tissue samples from the horses’ intestines to measure the concentration of activated neutrophils and to evaluate the organ’s outer layer for neutrophil infiltration. By comparing results from horses in the treatment group to animals in the control group, the scientists can determine whether lidocaine administered intravenously has any impact on neutrophil numbers.
And what if the lidocaine treatments appear to reduce neutrophil numbers and activity in the small intestine?
“I think horse owners will respond very positively because everything we’re trying is to prevent intestinal damage. If we can administer lidocaine and prevent any more intestinal damage, then horses with colic have a better chance of survival,” Shoemaker says.
As a result, surgical specialists may soon have a new, cost-effective method of treating and preventing colic surgery complications, says Shoemaker. “Hopefully, lidocaine equals fewer complications, fewer repeat surgeries … and fewer horses dying.”
Published with permission from Horse Health Lines, publication for the Western College of Veterinary Medicine’s Equine Health Research Fund. Visit www.ehrf.usask.ca for more information.
