Dialysis in Horses
- May 30, 2011
Your horse suffered a severe tying-up episode, and due to accompanying muscle degeneration your horse now has renal (kidney) complications. Or maybe your horse is experiencing renal dysfunction due to a toxic reaction to medications or from a massive infection. Your veterinarian administered the usual treatments to clear the toxins, but the kidney values remain dangerously high, indicating the kidneys are still unhealthy. Is there anything more you can do to save your horse?
In acute cases such as these, dialysis might succeed where other measures have failed. While it's an expensive procedure that rivals the cost of some colic and complicated orthopedic surgeries, and is yet not widely offered, it is an option.
"The purpose of dialysis is to remove the waste products that build up in the body and, in that respect, temporarily replace the kidney function," explained Laurent Couetil, DVM, PhD, Dipl. ACVIM, professor of large animal medicine and equine sports medicine director at Purdue University.
There are three different dialysis procedures: hemodialysis, peritoneal dialysis, and pleural dialysis.
With hemodialysis, a procedure commonly used in humans, the veterinarian places an intravenous (IV) catheter; blood is collected and transferred to a machine that filters toxins from the blood, and the filtered blood is returned to the patient through another vein.
"Hemodialysis has been described in a foal and the technique has also been recently reported in healthy adult horses," Couetil noted. "It's very involved, very cumbersome. The equipment is very expensive, the procedure is technically complex, and there are more potential complications with hemodialysis such as clotting problems because the blood comes in contact with nonbiologic membranes during the process."
Harold C. Schott II, DVM, PhD, Dipl. ACVIM, professor of large animal clinical sciences at Michigan State University's Veterinary Medical Center, added, "A few veterinary schools offer hemodialysis, but only for dogs and cats."
Intermittent peritoneal dialysis is the most commonly used form of dialysis in horses (such as in foals with bladder rupture) to stabilize them prior to surgery. With this procedure, the veterinarian places a catheter through the abdominal wall, then injects dialysate (a blood-cleansing solution) into the peritoneal membrane (lining of the inside of the abdomen), explained Couetil. While in the peritoneal cavity, the dialysate extracts toxins and excess fluid from the blood.
"The dialysate sits in the abdomen for about 30 to 60 minutes; the toxins pass from the blood into the solution," he said. Then we drain out the solution containing those substances from the abdomen."
Usually, peritoneal dialysis is performed on an intermittent basis, generally once or twice a day for a couple of days. However, in 2002, after intermittent peritoneal dialysis failed to sufficiently decrease a horse's toxin levels, Couetil administered dialysates in a continuous manner, a procedure used in human patients.
"As far as I know, continuous peritoneal dialysis had never been done in a horse before," he said. "With this procedure, we inserted two catheters in the horse's abdomen--one in the flank region to get the fluid in and one on the midline underneath the abdomen to recover the fluid."
Similar to the way IV fluids are administered in the stall, two bags were hung in the stall (one which dispensed the dialysates, the other which recovered the solution) for three days.
The continuous process succeeded. After four days of intermittent treatment, toxin levels remained 10 times higher than normal. But after three days of continuous treatment, levels dropped to just a twofold increase. The horse recovered, and two years later it was maintaining normal kidney values without further treatments.
Pleural dialysis is similar to peritoneal dialysis, except fluid is placed in the thoracic (chest) cavity instead of the abdominal cavity, explained Schott. This type of treatment is seldom used in horses, except when the abdomen cannot be used (such as after abdominal surgery). Although the fluid is easier to recover with pleural dialysis, there are numerous disadvantages.
Couetil explained, "The thorax is markedly smaller than the abdomen, therefore reducing the surface area available to perform the dialysis. More importantly, filling the pleural cavity with fluid will compress both lungs and heart, thereby affecting their normal function. You can infuse a lot of fluid into the abdomen before you start noticing abdominal discomfort (mares do fine with a 100-pound fetus plus 20 liters of allantoic fluid)."
The Ups and Downs of Dialysis
Dialysis isn't recommended for horses suffering from chronic kidney disease. In those cases, kidney damage is irreversible and dialysis on a regular basis is too impractical. However, dialysis could be beneficial in treating acute causes of renal problems: massive infections, myoglobins in the blood (from muscle breakdown), poisons, and drugs (such as gentamicin, if overdosed or used for an extended period of time).
"If you can address renal dysfunction early enough in the acute phase and address the primary problem, you could relieve the kidney function with dialysis, and that might give the kidneys enough time to recover and heal," Couetil said. "The horse may not return to completely normal renal function because there could be some permanent damage, but with the remaining kidney function, the horse could live normally."
Although dialysis is an option, Couetil said it should not be a first response: "Most of the time, IV fluids to help urine production is enough to help filter out the toxins. If that's not enough, we'll give diuretics to try to increase urine production. Sometimes that's not enough, so we'll administer drugs to increase blood flow to the kidneys. After doing all of those things, if the animal still cannot eliminate waste products sufficiently, we'd consider peritoneal dialysis, although just a minority of cases would qualify for this."
Additionally, there are a few drawbacks to dialysis.
Peritoneal dialysis is very time-consuming and expensive, prognosis of animals undergoing the procedure is fair to poor, and most veterinarians--even at referral hospitals--aren't currently offering the treatment.
Treatment must be performed at a veterinary referral hospital. The horse is sedated (not anesthetized), placement of the catheters and connection to the fluid bags take about an hour or so, and the horse needs close monitoring for the several days it takes to filter the blood.
"There are potential complications as soon as you enter the abdominal cavity," Couetil noted. "The risk of having an infection in the abdomen, creating a peritonitis (inflammation of the membrane lining the abdomen), is always there."
Treatment costs have run anywhere from $1,000 to as high as $20,000, although that price tag could start to come down, Couetil said.
"Now that we've shown it can be done and it's effective, I would use this technique earlier, which would cut down the total cost significantly--30-50%--instead of trying intravenous fluid therapy for days with no result," explained Couetil.
Costs for the horse receiving continuous peritoneal dialysis for three days at Purdue was about $9,900, which included three weeks of hospitalization.
He added that prognosis still varies depending upon the success of treating the primary condition and how long the renal insult continues before veterinarians implement treatment: "The longer the horse has been in renal failure, the poorer the prognosis. Acute cases that are treated early and aggressively have a better prognosis."
Because horses that recover usually don't regain all of their kidney function, they might drink significantly more water, urinate more, and thus require more frequent cleaning of their stalls.
"Also, any kind of further damage to the kidney that might occur later on could be more dramatic because the horse doesn't have as much kidney reserve," Couetil noted. "The owner has to accept these potential complications."
Although referral centers don't tend to offer peritoneal dialysis, there is no reason why they can't.
"The beauty of peritoneal dialysis is that, unlike hemodialysis, no special equipment is required," Couetil explained."It is no more complicated than placing drains in the abdomen for peritoneal lavage, which is a routine procedure nowadays."
In fact, Couetil anticipates that in the near future, peritoneal dialysis will be regarded the same way as peritoneal lavage is today: "We certainly have a lot of work to do in order to better define which type of renal problems will best benefit from peritoneal dialysis and to determine the optimum protocol. But hopefully, our experience will help clinicians move past the 'can't be done' or 'doesn't work' attitude. We said the same about colic surgery 30 years ago! I think we demonstrated the proof of concept."
About the Author
Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.
POLL: University Equine Hospitals