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Colic: Part 1: Diagnosis and Workup

Horse colic examination and anatomy
When talking about colic, it's important to have some idea of what the various parts of the equine gut are... So, here we go: Stomach - quite small, and hidden away deep up in the ribcage. Small intestine - this is very long, but quite narrow (perhaps 1 or 2 inches across). It is all coiled up throughout the abdomen. Large intestine - this is divided into three parts: The Caecum is a large sac perhaps four or five feet long, pointing forward, and can be heard on the right flank. Generally, it makes a loud gurgling noise every 20 to 30 seconds in a normal, healthy horse. The Large Colon makes up a double U shape, lying on the bottom of the abdomen. It can be up to a foot across, but at each end is a sharp 180-degree bend; the bend near the pelvis (the pelvic flexure) is especially narrow. The Small Colon runs from the large colon down to the rectum, along the top of the abdominal space.
It's something all horse owners dread - colic. However, colic is a symptom, not a disease in its own right, and has a wide range of different causes. This is the first in a three-part series where I'll be looking at colic in horses - its diagnosis and treatment, and what happens if your horse has to be referred for surgery. Put simply, all colic is, is abdominal pain. However, before you're tempted to dismiss it as a stomach ache, it's worth remembering that the horse's intestines are as complicated as a major chemical factory! Anything that causes disruption to their function is potentially life-threatening. Occasionally, colic pain comes from a non-intestinal source, e.g. Liver disease (think ragwort poisoning, or liver fluke), or a kidney issue. In mares, it can also be caused by certain disorders of the reproductive tract. However, the vast majority are due to disease, damage or malfunction of the intestines. If you call your vet and tell them that your horse has colic, they'll treat it as an emergency, because it can be. They'll generally take a bit of history from you, a quick description of what the horse is doing at the moment, and then they'll head out to examine the horse. Most vets will also give instructions for what to do while you're waiting; it's important to do what they say, not what someone else on the yard suggests. This is because they may have an idea what sort of colic your horse has, and will try to tailor their instructions to the specific case. For example, some forms of colic respond well to being trotted around on the lunge; however, that can worsen other types. When they arrive, the vet will want to establish three things: Firstly, does the horse actually have colic? I've been called out to "colic" cases that proved to be laminitis; to a mare foaling down; once even to a tired (but perfectly healthy) horse sleeping in his stable! Secondly, assuming it is a colic, is it a Medical or a Surgical Colic? (I'll talk more about this distinction in a minute). Third and finally, can they make a specific diagnosis of what kind of colic it is? Every vet will have their own routine, but my workup goes something like this: What's the horse's behaviour like? Is he alert, or dull and unresponsive? Is he thrashing about, or just looking at his flanks occasionally? Generally, a quieter horse is likely to have a milder colic, unless he or she is so toxic that they are depressed or spaced out. One exception is that some spasmodic colics are incredibly painful - however, the pain usually comes in waves. Are there any droppings in the stable? Hard, dry lumps of faeces is suggestive of an impaction, or blockage; while very runny faeces or diarrhoea may suggest colic secondary to an infection, e.g. Salmonella. Then I'll start my examination: Mucous membranes (gums are usually most accessible and reliable) - what colour are they, what is the refill time, are they tacky? The normal colour is described as being "salmon pink", and if you press with a finger for a moment, the colour should fade to white, then return within 2 seconds. They should also be nice and moist to the touch. If they are red, or purple, or the colour doesn't fade, it is highly suggestive of toxic shock (like septicaemia). This is a marker of a really, really severe injury to the gut wall, that’s allowing bacterial toxins to enter the circulation. If the refill time is greater than 2 seconds, or the membranes are tacky or dry, it suggests dehydration and/or shock. Heart rate - how fast, is the rhythm good? As a (very rough and ready!) general rule, a heart rate under 60 beats per minute implies a Medical colic, while over 80 suggests a Surgical case. If there's an abnormality in the rhythm, it can mean heart disease as well, or severe toxic shock. Gut sounds - what do the guts sound like in all 4 quadrants? This is where you'll see your vet putting a stethoscope to the horse's flanks, listening to the guts. The normal, healthy gut makes a wide range of bubbling, gurgling noises (the sort that anywhere else you would associate with really cheap plumbing!). The bottom left is the left Large Colon, bottom right is the right Large Colon and perhaps some Caecum, the top right is the base of the Caecum, and the top left is mainly small intestine. This is one of the most useful tests we can do - reduced sounds mean the guts are "slowing down" - this can mean an impaction or blockage, but it can also mean a serious disease e.g. a twisted gut. Increased sounds is generally a good sign, as it usually means a Spasmodic colic. Finally, I'd want to take the temperature (a horse with a fever is likely to have another disease, e.g. Salmonella, that is the underlying cause of the colic), and then, if at all possible, do a rectal exam. People get very excited about this, and it's one of the standard jokes about vets, but I'd like to go on record and say that I doubt anyone actually enjoys rectalling a horse! Apart from anything else, it's dangerous to the vet, and uncomfortable to the horse... However, it can provide more information than almost any other test. What we're feeling for is anything unusual: is the large colon a normal size and texture? How about the Caecum? Can you feel the small intestine? Usually, the small intestine is almost impossible to feel - it just slithers out of the way. If, however, you can feel thick, swollen loops of intestines (they feel a bit like black pudding, or really thick, soft sausages, if you're interested!), it is an indication of a complete blockage in the small intestine, which needs emergency colic surgery. On the other hand, if you feel a doughy, squishy mass in the colon, that means the horse has an impaction. Sometimes, if there is doubt about whether food is passing from the stomach or not, the vet will pass a stomach tube and see how full the stomach is. This looks really easy in theory - you pass a tube up the horse's nose, he swallows it, and then you syphon out the stomach. If you get lots, it's too full, if not, it's fine. However, not all horses are quite so easy! Some horses are really difficult to get to swallow the tube, and it can take several attempts to make sure it's not in the windpipe (which would be a disaster). Also, the equine stomach is, as one equine surgeon I know once put it, "a fantastic organ - it can be completely dilated (full), and you'll get nothing out of it until you move the tube half an inch, then it all comes spurting out". However, if there's any doubt, it can be a great tool to ensure that there isn't a rapidly life- threatening blockage; it can also be emergency first aid to prevent the horse's stomach rupturing in a severe surgical colic. The vet will also sometimes take blood samples - we tend to hold onto these in case they're needed, but the main things we're looking for are: 1) Evidence of dehydration - the blood tests will allow us to quantify the degree of dehydration, making it easier to plan a course of treatment. 2) Evidence of infection - if the white cell count is significantly abnormal, it suggests there may be something else causing the colic that we might need to look into. 3) Liver and kidney function - sometimes liver or kidney disease can present as colic 4) MOST IMPORTANTLY - Fibrinogen levels. Fibrinogen is a substance that can be used to assess inflammation and tissue damage - a high Fib level in a colic case is very suggestive that the gut integrity is damaged, and that surgical intervention may be needed. There's one other sample that can be very useful, especially as a "rule out" test if the clinical findings are contradictory or unclear. This is a peritoneal tap. This test carries some risk, but sometimes it's the best way to find out what's going on inside the abdomen. The belly of the horse is clipped, and prepared so make it as sterile as possible - we don't want to risk introducing infection. The area is numbed with local anaesthetic, and then either a small incision is made with a scalpel and a blunt cannula inserted or (more usually) a small sterile needle is VERY CAREFULY inserted through the abdominal wall. The fluid that comes out is collected in a sterile sample pot for examination. The risk, of course, is that damage is done to the intestines; however, we're very careful to avoid them as far as possible, and instead to collect the fluid that surrounds the intestines, the peritoneal fluid. In the lab, the numbers of cells can be counted to assess if there's infection in the belly (peritonitis); however, in the field we can tell three things: 1) The tap fluid is clear (you can read text through it) yellowish - this suggests that the abdomen is basically OK, and means that in the absence of any other findings, the case can be managed medically. 2) The tap is cloudy, reddish or umber in colour - this means severe damage to the gut walls and/or peritonitis (infection in the abdominal cavity). This horse needs urgent referral for investigation at a hospital. 3) The tap contains gut contents (green or brown, lumpy) - sadly, this means that the intestines have ruptured; the horse is highly unlikely to survive. Alternatively, this may mean that the needle has gone into a part of the intestines, so if I get this, I'll usually repeat the tap a few inches away, to make sure. If the needle has damaged the intestine, it's not a disaster, but it is something to be avoided if possible. So, using all the information from our history and workup, the vet has to decide if the colic is Medical or Surgical. The terms are more or less self-explanatory: a medical colic can be managed with drugs, while a surgical colic needs emergency surgery. As a rule of thumb, 9/10 colics are medical, and can almost always be managed on the yard. In my next blog, I'll be looking at these Medical colics, their causes and treatment. If you are worried your horse or pony may be suffering from colic, talk to your vet, or check the symptoms using our Interactive Equine Symptom Guide to help assess how urgent the problem may be.
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