Evaluating equine colic: Surgeon's perspective (Proceedings)

Colic in the horse makes up a large part of equine veterinary practice. The term colic is actually a general term for any causes of abdominal discomfort. The majority of causes of colic stem from abnormalities in the gastrointestinal tract. However, non-gastrointestinal causes also exist, and should not be overlooked. Cases of colic in the adult horse and in horses less than 6 month old should be examined slightly differently, as the most common etiologies are different for these two groups.

Most clinicians are familiar with the classic signs of equine colic, including, pawing, kicking at the abdomen, and rolling. Some other more subtle signs of colic include raising the upper lip repeatedly, backing up into walls, repeatedly extending the penis, and dog sitting. It is important to know what behaviors are abnormal for each individual horse, as some of these signs can occur normally in certain individuals. Each individuals response to pain is different, and there seems to be some breed differences as well. In my experience, Tennessee Walking Horses and Standardbreds seem to be very tough in their response to painful stimuli, whereas Arabians and Warmbloods seem to be not as stoic.

Examining equine colic is like putting a puzzle together to try and arrive at a diagnosis. The pieces to the puzzle include the physical exam findings, rectal exam, laboratory analysis, nasogastric intubation, and abdominal ultrasonography. All of these pieces must be evaluated prior to formulating a treatment plan. The key to generating the necessary working data base from which to make treatment decisions is to have a repeatable examination technique that works for the individual veterinarian. With experience, comparing an affected horse to others with colic can assist in the decision making process.

Historically, veterinarians have lumped the treatment of colic into two broad categories: surgical treatment and medical treatment. However, there is a lot of overlap in these two categories as well as transfer from one category to another. I prefer to examine each animal as an individual, try to arrive at a diagnosis, and initiate treatment. In complicated cases the treatment will need to be modified as the situation changes. I view surgical intervention as part of the medical treatment in certain cases, and as a piece of the diagnostic puzzle in other cases, as it is in most cases an exploratory laparotomy.

Every examination should begin with a thorough history. Important information to obtain includes the duration of the problem, severity and types of clinical signs, treatment prior to the evaluation, and any concurrent problems that the horse may be currently receiving medication for. Also I like to find out if the horse has experienced other episodes similar to this one, as well as the treatment and outcome. In most situations, the time that it takes to get a rectal temperature should be adequate to obtain all of the pertinent history. During this time you should also be able to get a visual impression of the severity of pain that the horse is in now or has been in the past. The presence of abrasions or other wounds around the eyes and head indicates that the horse has experienced severe pain. The experienced practitioner can usually get a good feel for which way a case will go based on the ÒlookÓ of the horse, even prior to laying your hands on the horse.

After I have obtained the history, a thorough physical examination beginning with the vital signs is started. Even in cases of severe abdominal pain, the initial vital signs should be obtained prior to administering any medications, as pharmaceuticals can cause profound alterations in these values. Body temperature determination is critical in all cases of colic, and must be performed prior to rectal examination, as the pneumorectum induced by transrectal palpation will cause an artificially low temperature. Most horses that have a simple gas colic will be normothermic. Additionally, most cases of colic in need of surgical correction will also be normothermic. If a horse has been rolling a lot and the ambient temperature is high, a mild increase in the temperature can be due to exertion. Also, horses coming off of a trailer on a hot day may have an artificially mildly elevated temperature. Horses with inflammatory or infectious conditions of the intestinal tract, such as proximal enteritis or colitis, will often times be febrile. However, if the horse received a non-steroidal anti-inflammatory by the owner prior to your examination, the temperature could be artificially normal. Also, severely dehydrated and shocky animals may be hypothermic, reflecting the severe nature of their problem.

Heart rate is extremely important in evaluating cases of colic. A normal heart rate generally indicates a mild problem, although I have seen horses with surgical lesions, particularly large colon displacements, with normal heart rates. Again it is important to evaluate the heart rate prior to the administration of any medications. Alpha 2 agonists (detomidine, xylazine, romifidine) can cause profound depression of the heart rate. Mild elevations in heart rate should not be over-interpreted in anxious horses or horses brought into a new environment for their examination. If these horses are allowed to settle down the heart rate may return to a more accurate, lower level. It has been shown that adult horses with sustained heart rates of greater than 60 beats per minute have decreased prognosis for survival, as this generally indicates more serious problems. When heart rates start to exceed 60 in the adult horse, there is often a severe abdominal derangement causing dehydration, endotoxemia, and pain. Serial heart rate calculations can also be used to monitor the response to treatment or determine if the lesion is deteriorating.

Thoracic and abdominal auscultation are usually performed next. The respiratory rate should be obtained, but perhaps is the least useful of the vital sign parameters. Respiration rates can be elevated with pain and fever. In horses that have abdominal distention, the respiration rate is usually increased and shallow. With severe distention, the ability to ventilate can be drastically altered. The thorax should also be carefully auscultated as pleuritis and diaphragmatic hernia can both lead to signs of colic. Auscultation of the abdomen should be done to detect the presence or absence of gastrointestinal borborygmi, as well as the nature of the borborygmi. Generally the abdomen is divided into four quadrants, each one representing a different part of the gastrointestinal tract. I like to characterize the gut sounds as hypermotile, hypomotile, or absent. In geographic areas where there is a lot of sand colic, often times the sand can be ausculted on the ventral midline. Contour of the abdomen should be ascertained, as abdominal distention can be a sensitive indicator of the need for surgery.

Evaluation of the mucous membranes gives good insight into the cardiovascular status of the animal. The mucous membranes should be a nice pale pink color and be moist to the touch with a capillary refill time of less than 2 seconds. Dark or injected mucous membranes often indicate endotoxemia and severe cardiovascular compromise. Very pale or white mucous membranes usually indicate that the horse is hemorrhaging. This finding is particularly critical in the post-foaling broodmare. The skin tent test can also be performed to help determine hydration status, but should not be over-interpreted. Again serial determinations of changes in mucous membrane character may be used to assess the improvement or deterioration of the condition.

In addition to the above mentioned aspects of the physical exam, all intact males should have their testicles palpated. An enlarged, painful testicle or scrotum is most often indicative of inguinal or scrotal herniation.

Once all of these non-invasive parameters are obtained, I generally proceed with trans-rectal palpation and nasogastric intubation. I like to perform the rectal examination first if possible, as these findings may dictate particular treatments with regards to nasogastric intubation. First and foremost, safety for you and for the animal should be attended to. Proper restraint and handling is essential, and even with that it may not be possible to perform these procedures in every animal.

In horses that have never been rectally palpated before, I will infuse 30-60 cc of lidocaine into the rectum 2-3 minutes prior to my examination. This is generally all that is necessary for me to get a complete rectal examination. In some horses, the administration of buscopan is necessary for complete rectal relaxation. During my examination, I first try and decide if it is a normal or abnormal rectal examination. Sometimes this is all that can be determined. If I decide that the examination is abnormal, I try to decide if the abnormality is arising from the large intestine, small intestine, or small colon. One should be familiar with the feeling of the external surface and size of each of these parts of the intestine. Occasionally an exact diagnosis can be made. This is particularly true in cases of nephrosplenic entrapment, large colon impaction, and small colon impaction.

Passing a nasogastric tube should be attempted for every horse with colic. This is particularly important for horses with severe abdominal pain as severe gastric distention can lead to rupture if the stomach is not decompressed. An attempt should be made to check for reflux in every horse prior to administration of any medication. I am not a big fan of using mineral oil, as I do not feel strongly that it helps break down impactions, and I do think that it could be potentially harmful in horses that have compromised intestinal mucosal barriers. It is also difficult to manage in surgical colics where an enterotomy is necessary, as mineral oil is difficult to clean off of the bowel wall. Alternatively, if I feel that there is an impaction or if the horse is dehydrated, I will administer straight water in the place of mineral oil, but only if there is no positive net reflux.

These physical exam findings are usually enough to make a tentative diagnosis and formulate an initial plan. In my situation, I am evaluating these horses in my clinic, and many of them have been previously treated or are being referred by another veterinarian. Therefore, in most cases a full complement of blood work is performed, including complete blood count with differential, fibrinogen, chemistry analysis, electrolytes, and blood gas values. All of these values can be useful to assess the entire systemic status of the animal. The total white blood cell and neutrophil count are particularly useful as a neutropenia and leukopenia usually indicate an inflammatory process such as enteritis or colitis. Mild elevations in the neutrophil count, in the absence of any other abnormal findings, may be the result of endogenous cortisol release due to the stress of the situation. Hematocrit and total protein together are also very useful to assess the hydration status of the animal. They should be evaluated together because the equine spleen can harbor a large amount of blood cells which may be released by splenic contraction during times of stress, causing an artificially high hematocrit. Increases in total protein occur due to dehydration primarily, but some severe inflammatory conditions may lead to this due to a hyperglobulinemia. Decreases in total protein typically occur due to losses into the peritoneum or gastrointestinal tract. This can be seen in diseases such as enteritis, colitis, and peritonitis.

Another useful diagnostic tool is abdominal ultrasound. Ultrasound enables you to evaluated areas of the abdomen not accessible to transrectal palpation, and is less invasive so can used in horses not amenable to rectal palpation, including foals. In fact, abdominal ultrasound is probably the single most useful diagnostic for use in foal colic. Abdominal ultrasound is particularly useful to pick up small intestinal distention. When small intestinal distention is visualized, size and motility can be evaluated. Small intestinal distention with progressive motility is most likely due to a non-strangulating small intestinal lesion, such as ileal impaction or enteritis. Amotile distended small intestine is most often caused by a strangulating lesion, thus giving more evidence for surgical intervention. Another very useful and simple area to examine with the ultrasound is the nephrosplenic space. In normal horses, the left kidney can be visualized just deep to the spleen in approximately the last intercostal space. In horses with nephrosplenic entrapment, the spleen can be visualized but the left kidney is hidden by the gas within the entrapped bowel. Ultrasound can also be used to evaluate abnormalities in thickness of the bowel wall, or to see increased amount of peritoneal fluid.

Abdominocentesis can be used to help evaluate the health of the intestine. However, I rarely use this diagnostic unless I suspect a rupture. For me the information coming from the results of an abdominocentesis is not sensitive enough to warrant the added risk of the procedure. When I do perform abdominocentesis, I will use the ultrasound to dictate the best location to find fluid.

In areas of the country where enterolithiasis is common, abdominal radiology can be used to help determine this cause. This requires high output radiographic machines to be able to penetrate the adult horse abdomen. Abdominal radiographs can also be used to check for sand in the intestine. Alternatively, abdominal radiography in the foal or miniature horse can be useful and does not require special radiographic equipment.

Gastroscopy can also be used in horses to detect gastric ulceration. This does however require that the stomach is relatively empty for a diagnostic study. Generally, horses must be fasted from food for a minimum of 12 hours, and from water for a minimum of 6 hours in order to get the stomach empty enough for complete evaluation.

Fortunately, most cases of equine colic require simple one-time treatment. When a veterinarian is called out the second time for the same problem, I generally recommend referral to a hospital unless there is a certain diagnosis, and things are moving in the right direction. In the past, I feel that veterinarians have used referral as a last ditch effort when all other treatments have failed at the farm. I think we need to re-think this and refer horses to a hospital situation based on their clinical signs, and not just based on the need for surgical intervention. I feel that treating horses in this manor drastically improves the prognosis. Many of the horses in my practice area are referred to the hospital simply for 24 hour observation when a diagnosis is not certain. As a surgeon, I would much rather have a horse come for observation and not require treatment then to have one sent in a compromised systemic status.

The most critical pieces of the puzzle that I use to decide to take a horse to surgery include degree of pain and response to treatment, abdominal distention, copious nasogastric reflux with no abatement of discomfort, and certain rectal examination or abdominal ultrasonographic findings. I consider myself a fairly aggressive surgeon, as if I am not certain of a diagnosis and I dont feel comfortable waiting, I will recommend exploratory surgery. The morbidity and mortality of this procedure in an uncompromised patient is much less than it used to be. I probably operate on some horses that could get over the problem without surgery, but I would rather open the horse, have an exact diagnosis, and fix the problem before the intestine becomes damaged. Also, I have found that horses whose problems are fixed surgically very quickly require much less post-operative treatment, have shortened hospitalization periods, and have a better prognosis than those horses that linger around the hospital for several days prior to surgical intervention. This reflects in a reduced cost of treatment as well.

The mainstays of medical treatment include a non-steroidal anti-inflammatory medicine (flunixin meglumine) and either intravenous or enteral fluid therapy. Immediate analgesia can be obtained by using alpha-2 agonists such as xylazine or detomidine. If necessary, an opiate such as butorphanol can be added with an alpha-2 agonist. With any of these medications, the need for repeated administration should arise a warning flag, as most simple cases of colic do not require treatment more than once. A relatively new drug available in the United States is N-butylscopolammonium bromide (buscopan), an antispasmodic and anticholinergic drug. The drug is labeled for the control of abdominal pain associated with spasmodic colic, flatulent colic, and simple impactions. This drug will cause an elevation in heart rate and decrease in borborygmi for 30 minutes post administration, so it is important to get an accurate measure of these values prior to the horse receiving the medication. An additional use for this drug is that it causes profound rectal relaxation, so that it can be used in horses that are extremely resistant to rectal examination. Similar to the above mentioned medications, repeated administration of buscopan is not recommended.

For some horses, the treatment decision is simple and straight forward: they either need surgery or they dont. However, for the mass majority of cases, the decision is not that easy. This is where all of the clinical exam and diagnostic findings or pieces of the puzzle must be put together to arrive at a working diagnosis. Also in many complicated cases, serial examinations are necessary to determine if the case is responding to treatment. With advances in surgical and anesthetic techniques, colic surgery is no longer a death sentence for horses. The most important factor affecting the prognosis is prompt attention and effective decision making.