Page 18 - August 2005 The Game
P. 18

18 The Game, August 2005 Your Thoroughbred Racing Community Newspaper
THE ODDS ON COLIC SURGERY
Once upon a time, colic surgery was a frighteningly risky undertaking. Between the surgery itself and the dangers involved with putting horses under a general anaesthetic, it was the sort of thing you only chanced with an extremely valuable animal - and you’d do it knowing the odds of survival were slim.
Today, committing a horse to surgery is a much more optimistic decision. Advances in anaesthesiology have had much to do with that “putting a horse Îunder”, and bringing him back to consciousness safely, has improved by leaps and bounds in the last few decades. But one still couldn’t consider colic surgery exactly routine or risk-free. Faced with making the choice of whether to put a horse under the knife, most caretakers would like to have an idea of the odds of the horse’s survival and recovery. That was the impetus behind a recent study from North Carolina State University’s College of Veterinary Medicine, outlined by
Anthony Blikslager DVM, Ph.D., Dipl ACVS at the 43rd annual British Equine Veterinary Association Congress in September, 2004.
Of horses presented for evaluation of colic at
NCSU who go to surgery, approximately 25% are
lost during the surgery, Blikslager says. Contributing factors include discoveries like gastrointestinal ruptures, sections of dead bowel
which are beyond the reach of the surgical team, or multiple severe lesions which might lead the surgeons to recommend euthanasia of the horse before he comes out of the anaesthetic.
Of the horses who undergo surgery and recover from the anaesthetic successfully, approximately 80% are ultimately discharged from the hospital according to the NCSU data. But you couldn’t say these horses are out of the woods just yet. Long-term complications will eventually claim another 10 to 15% of these horses, generally thanks to one of three conditions: postoperative ileus (intestinal
obstruction), shock, or intra-abdominal adhesions which form as scar tissue begins to form after the surgery.
In one study of 259 surgical colic cases, more than half of the fatalities occurred in the first seven to 10 days after surgery. Post-operative ileus and shock accounted for the vast majority of those deaths. (In another study, ileus was identified as the cause of 40% of the post-operative deaths.)
A horse with an ileus can be identified if a nasogastric tube is slipped into the stomach post-surgery, which is generally done only if the horse has an elevated heartrate or is showing other signs of abdominal pain. If a blockage is present, the veterinarian can sometimes collect litres of refluxed material through the tube - a bad sign, since the risk of mortality when this happens is more than eight-fold. The good news is the risk of an ileus can be substantially reduced by using drugs which encourage gut motility, and religiously hand-walking the patient during his initial post-surgery hospitalization.
Horses at risk for adhesions often exhibit recurrent colic signs and the risk goes up in a horse who has had more than one colic surgery. Unfortunately, adhesions often affect horses after they’ve been discharged from the hospital, when they’re no longer under 24-hour supervision.
As for shock - post-surgery, veterinarians watch closely for any of the following signs, which are strongly associated with mortality:
• a heartrate of more than 60 beats per minute in the first 24 hours post-surgery
• slow capillary refill time (longer than two seconds)
• abnormal mucous membrane colour
• packed cell volume (PCV) greater than 42% in the first 24 hours (normal is 31-47%)
• total plasma protein less than 5.5 g/dL in the first 24 hours (normal is 6-7.5 g/dL).
Other factors increase the risk of mortality, post-surgery, include endotoxemia, septic peritonitis, and unusual drainage from the incision (which ups the odds ratio 3.2 times).
Horses who undergo surgery for “twisted gut” (usually the large colon) always have a guarded prognosis for survival. Generally, the twist means that a section of the colon has died and will need to be cut out and the gut re-joined. In one study, the survival rate for these cases was a little better than 50%.
The news is also less than rosy for geriatric patients. Blikslager and his colleagues found that horses over 20 years of age were 5.5 times less likely to survive colic surgery than younger horses, mostly because they are at high risk for a particularly dangerous type of colic: strangulated lengths of intestine thanks to the formation of a fatty abdominal tumour called a lipoma. Lipomas form on stalks which tend to tangle themselves around lengths of the intestine and strangle them; by the time surgeons open the horse up, there are often extensive sections of dead bowel. Geldings are at higher risk for lipomas than mares or stallions, and horses with a high percentage of body fat are also more likely to develop these tumours. It’s thought that older horses are at higher risk for lipomas simply because they take many years to develop.
Recovery from colic surgery is a strenuous process, requiring good muscular strength and energy reserves, so owners may wish to seriously consider the repercussions of the recovery phase in very old horses, Blikslager says. But if your geriatric horse is still in relatively good shape, he should still be considered a reasonable surgical candidate, especially if your veterinarian thinks the colic is due to impaction (often a side-effect of failing teeth) rather than a lipoma. It’s all about weighing the odds.
Equine Health
by Karen Briggs
Dave Landry Photo
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