Colic Diagnosis in the Horse

A thorough and detailed examination of a horse with suspected gastrointestinal tract disorders is extremely important. After taking a history from the owner,a logical process including the examination of other body systems as well as the gastrointestinal tract should be followed. The examination usually starts at the head and proceeds caudally. Many different diagnostic tests can be used to diagnose the cause of equine colic, which may have greater or lesser value in certain situations. The most important distinction to make is whether the condition should be managed medically or surgically. If surgery is indicated, then it must be performed with utmost haste, as delay is a dire prognostic indicator. Repeat examinations are vital in assessing changes in the horse's condition and level of pain. They should be conducted every one to two hours by the owner or veterinarian and any changes should be managed appropriately and the re-evaluate the horse's prognosis.

History

A thorough history is always taken, starting with the signalment (age, sex, breed). The history can be broken into an early history and a recent history. It is an important first step in determining the cause of the colic.

Early History

• Has there been any recent changes in management (feeding/diet changes, water,recent box rest, deworming, medication, exercise routine, breeding, pregnancy)?
• Has the horse ever had any previous episodes of colic?
• How long since the onset of clinical signs? This has a profound impact on prognosis, and the type of treatment that will be undertaken.
• Is the horse eating and drinking normally?
• Does the horse drop food any food from its mouth during eating?
• Does the horse salivate excessively when eating?
• Has the horse made normal faeces or had any diarrhoea?
• What is the vaccination, deworming and dental prophylaxis of this and other animals at the yard?
• Are any other horses on the yard showing similar signs?
• Does the horse live outdoors or stabled?
• Does the horse live in an environment with much sand?

Recent History

• Is there evidence of abdominal pain?
• Is there evidence of weight loss?
• When did the horse last defecate?
• What signs has the horse shown (flank watching,pawing,rolling, kicking at abdomen) and has it changed?
• Has the horse received any treatment and how has it responded?

General Physical Examination

A physical examination including the following parameters should be carried out immediately and thoroughly.

• Attitude and External appearance
• Abdominal contour (distention-unilateral vs. bilateral)
• Body Temperature
• Heart Rate and Pulse character, Respiratory rate and effort
• Skin Turgor, Mucous membrane color and moisture, Capillary refil time (CRT)
• Presence of digital pulses

Attitude and External Appearance

It is important to assess the degree of pain. It is best do keep the patient in a quiet environment to fully assess them. If the owner or trainer of the horse has administered any treatments then the patients status may not be a true reflection of the clinical condition. If the horse is in severe, unrelenting pain and it is difficult to assess it safely, it is advisable to administer some analgesics, sedation and butyl-scopolamine prior to the examination. It is useful to get the heart rate prior to the administration of these medications due to their transient effects on the resting heart rate.

A horse with severe pain that is unresponsive to analgesics warrants going to surgery as soon as possible if it is a case of a strangulating obstruction. Multiple abrasions around the head and periorbital area indicate that the horse is experiencing severe pain. The duration of clinical signs is important to note as once the strangulated portion of intestine degenerates to a certain point, the pain will subside but the horse becomes increasingly depressed.

Non-infarctive conditions such as impactions and some ileal intussusceptions are demonstrated as intermittently, moderately painful cases.

A depressed horse that is pyrexic and displaying signs of moderate abdominal pain may indicate an inflammatory condition such as an enteritis, colitis of peritonitis.

The examination should also include the mouth for the presence of malocclusion, dental abnormalities, damage to the lips and gums, nasal discharge and excessive salivation. The abdominal contour should be examined for any swellings or recent enlargements which could indicate edema or umbilical, abdominal or scrotal herniations.

Abdominal Distension

Any degree of abdominal distension is usually indicative of a condition affecting the large intestines, as distension of the stomach and small intestine would not be large enough to be visible externally.

Body Temperature

Pyrexia may indicate an inflammatory or infectious condition and should be interpreted with other diagnostic tests such as fecal samples, hematology, biochemistry and blood cultures.

Cardiovascular Parameters

Tachypnoea and tachychardia can be seen in the horse with colic. This is due to pain, but mainly due to decreased circulating volume, decreased preload, and endotoxemia. The rate should be measured over time, and its response to analgesic therapy ascertained. A pulse that continues to rise in rate to 60 to 70 beats per minute and weaken in quality over 6 to 8 hours in the face of adequate analgesia is considered a surgical indication. Infarctive disease is characterised by an increaseing, non-fluctuating heart rate.

Mucous membrane colour and moisture and capillary refil time (CRT) can be assessed to appreciate the severity of haemodynamic compromise.A reduced skin tent indicates dehydration. The mucous membranes change from pink and moist to red and dry as the circulating blood volume decreases. Reddening of the mucous membranes indicates haemoconcentration and worsens as the patient goes into shock. Reddening reflects worse prognosis, and cyanotic membranes indicate a very poor chance of a positive outcome as it it indicates that the horse is in endotoxic shock. A reduced skin tent indicates dehydration.

Auscultation

Auscultation of the abdomen for intestinal borborygmi, usually performed in a four quadrant approach, can be a useful tool. Increased borborygmi are not usually associated with major changes, and may be indicative of spasmodic colic, or impending diarrhea. Increased borborygmi can be found early on in cases of enteritis, colitis and intestinal obstruction. Later in the progression of the disease there is decreased borborygmi due to the pain and inflammation associated with the gastrointestinal tract. Decreased borborygmi, or a sustained absence, may be suggestive of serious and potentially irreversible changes to the intestine. Trapped gas (tympany), particularly in the caecum and colon, can often be heard as a high pitched "pinging" during concurrent auscultation and percussion of the right (caecal) and left (colonic) flanks. Auscultation of the ventral abdomen over a 5 minute period can also be useful in regions where sand impaction is common. Auscultation reveals a sound similar to that of an ocean wave in these patients.

Rectal Examination

Sequential rectal examinations are the cornerstone of colic diagnosis, as many large intestinal conditions can be definitively diagnosed by this method alone. Rectal examination is invaluable in the diagnosis of medical problems such as primary impactions and spasmodic colic, and also in determining the severity of the disease and if surgery is necessary. Many subtle changes can be detected before they become apparent clinically or in the peritoneal fluid. A thorough rectal examination is vital for the early diagnosis and referral of surgical cases which improves the prognosis and post operative survival.

Abnormal Rectal Examination Findings

• Cecal Gas
• Distention of the large or small colon (gas or ingesta)and volvulus
• Intramural or mesenteric edema
• Herniation
• Impaction
• Intussusception
• Intraabdominal hematoma, abscess, mass
• Volvulus of the mesenteric root
• Enterolithiasis

Naso-gastric Intubation

Passing a Naso-Gastric Tube is useful both diagnostically and therapeutically. It should be performed in any patient with colic in order to determine if gastric distention is present and to relieve it. Therapeutically, gastric decompression is important, since horses are unable to vomit.Fluid is refluxed from the stomach, and any more than 2 litres of fluid is considered to be significant and indicates that surgery is necessary. Increased fluid is generally a result of backing up of fluid through the intestinal tract, due to a downstream obstruction. More than 2 litres of nasogastric reflux can be caused by a primary disorder of the small intestine or stomach. Horses with anterior enteritis have large volumes (10 to 20 litres) of reflux. Large colon obstructions such as a torsion can produce reflux due to secondary ileus and compression of the small intestine which prevents gastric emptying. The quantity, smell, content, and pH of the fluid should always be assessed. Blood-tinged, foul-smelling reflux indicates a severe anterior enteritis or a strangulating small intestinal obstruction. In these cases, gastric fluid will continue to build up and so the tube should be left in place to prevent a fatal gastric rupture.

Clinicopathologic Evaluation

Laboratory tests can be performed to assess the cardiovascular and metabolic status of the patient.

• Packed Cell Volume (PCV)
• Total Plasma Protein (TPP)
• Complete Blood Count (CBC)
• Blood Gases
• Electrolyte levels

Repeat PCV, TPP and CBC should be performed in less critical patients as a guide to response to therapy. In more severe or recurrent cases of colic, theses tests should be performed alongside blood gas analysis and electrolyte levels.

Packed Cell Volume and Total Plasma Protein

Packed Cell Volume (PCV) and Total Plasma Protein (TPP) are a measure of hydration status in the horse with abdominal pain. Intestinal disease and dysfunction causes hypovolaemia which result in dehydration. Increasing values over repeated examination and values over 45% are considered significant. The total protein (TP) of blood may also be measured, as an aid in estimating the amount of protein loss into the intestine. Its value must be interpreted along with the PCV, to take into account the hydration status. The PCV and TPP rise together in dehydration.

An increasing PCV without a corresponding rise in TPP may indicate that protein is being lost from the blood into the intestinal lumen or peritoneal region. It may also be due to the spleen contracting and releasing more red blood cells into the circulation in response to endotoxin release or sympathetic nervous system innervation.

Complete Blood Count

A Complete Blood Count can be useful in the colic patient. In cases of acute inflammatory disease such as colitis and enteritis, a leucopaenia (<4000 cells/ul)with a left shift and toxic neutrophils can be seen. Septic peritonitis due to a ruptured intestine will also show a severe leucopaenia (<1000 cells/ul. In chronic peritonitis due to intraabdominal abscesses, a high TPP and high fibrinogen levels alongside a mature neutrophilia will be seen. There are no major changes in the CBC White blood cell count in the early stages of simple and strangulating obstructions. Changes are apparent in the terminal stages.

Blood Gases

A metabolic acidosis with respiratory compensation is a common abnormality seen in colic. Typical values include pH 7.3 units, PCO2 35 mmHg and HCO3- 15 mmol/L. Horses with simple obstructions may show an insignificant base excess compared to those with a strangulating obstruction showing a significant base deficit. It is important to monitor and correct the acid-base imbalances especially for horses that will undergo anethesia and surgery. Rapid deterioration in acid-base status is a poor prognostic indicator.

Serum/Plasma Electrolyte levels

This is the least useful of the hematological tests for establishing a diagnosis in the colic patient, however its importance lies in the management of patients before, during and after surgery.

Hypocalcaemia can cause ileus and abdominal pain. Patients with colitis may have a hyponatremia and hypochloremia. Gastric dilatation results in the sequestration of fluid and hydrochloric acid in the stomach, leading to dehydration, hypochloremia and alkalosis. The same principle applies to large colon obstructions where fluid is trapped in the intestinal lumen causing dehydration and hypochloemia.

Blood and peritoneal lactate levels are useful in determining severity of disease and as a prognostic indicator. Blood levels between 1-2mmol/L are considered normal, while levels above 5.7mmol/L suggest hypoperfusion secondary to dehydration and/or a local ischaemia or strangulating obstruction. Elevated lactate concentrations in the peritoneal fluid are more suggestive of a strangulation.

Horses with dehydration and endotoxaemia may develop a pre-renal azotaemia (increased urea and creatinine).

Increased serum GGT concentrations indicate liver disease. Increased serum bile acids indicate cholestasis. Increased bilirubin levels can be due to anorexia, hemolysis or a hepatopathy.

Muscle damage in horses with severe pain and self-inflicted damage will produce elevations in AST, LDH and creatine phosphokinase.

Abdominocentesis

The extraction and analysis of fluid from the peritoneum can be useful in assessing the state of the intestines. Abdominocentesis can be a useful diagnostic tool in determining whether the colic patient should go to surgery. It should be performed in every case of recurrent, moderate to severe or persistent colic. It should not be performed in the field due to the risks to the veterinarian and horse if the physical examination findings are suggestive of the need for surgery and referral. For normal peritoneal fluid analysis in the horse click here.

In the early stages of simple obstruction of the small and large intestine, the peritoneal fluid will look normal. A cloudy fluid is suggestive of an increased number of white blood cells, which indicates the disease is relatively advanced. The protein level of abdominal fluid can be analysed, and may also give information as to the integrity of intestinal blood vessels. Elevated lactate levels in the sample can also give an indication of the degree of compromise to bowel, particularly as a peritoneal:peripheral lactate ratio. A sanguinous fluid can be caused by an infarction, which indicates surgery is necessary. The peritoneal fluid of a case of infarction will also have an increased total protein concentration and nucleated cell count. However, sanguinous fluid can also be caused by external trauma (e.g. rib fractures), middle uterine artery rupture in post-foaling mares, intra-abdominal hemorrhage, intestinal necrosis, splenic puncture or by inadvertent bleeding caused by the veterinarian. If the spleen has accidentally be punctured then the fluid will have a greater PCV than the blood and will contain lots of small lymphocytes. Intra-abdominal hemorrhage will have a fluid with a PCV lower than the blood, few if any platelets and evidence of erythrocytophagia. Peritoneal fluid that contains food material can indicate rupture of the gastro-intestinal tract, although care should be taken that intestine has not been punctured inadvertently. The peritoneal fluid of a case with bowel rupture will be dark, turbid and smell of ingesta. It will have an increased total protein concentration due to intestinal necrosis and an increased nucleated cell count with intracellular bacteria and plant material evident grossly and microscopically.

A normal peritoneal fluid sample does not rule out a strangulating lesion. For example, in the case of a diaphragmatic hernia, the strangulating gut is contained within the thoracic cavity, so will not affect fluid within the abdominal cavity. A similar situation is true of intussuception, where the strangulating gut is contained with another piece of non-strangulating gut.

Faecal Examination

The amount of faeces produced, and its character can be helpful, although as changes often occur relatively distant to the anus, changes may not be seen for some time. In areas where sand colic is known to be common, or if the history suggests it may be a possibility, faeces can be examined for the presence of sand, often by immersion in water, or simply by its texture. The presence of diarrhoea is common in sand colic, and can be seen in horses with enteroliths. Otherwise, diarrhoea is usually indicative of a non-surgical condition, although it can be associated with life threatening conditions such as salmonellosis.

Abdominal Ultrasound

Ultrasonographic evaluation of the abdomen is extremely useful in characterizing certain components of the disease process. The amount and character of free abdominal fluid can be determined, as well as the determination of a specific place for safe, high-yield abdominocentesis. The appearance of small intestine, including distension, wall thickness and motility (or lack thereof, often seen as sedimentatioon of digesta) can be extremely important in the decision for surgical or medical therapy. The large colon and cecum can be evaluated for wall thickness (particularly useful in cases of right dorsal colitis), fluidy contents (colitis/diarrhea), and sometimes displacement. The presence of mesenteric vessels associated with the large colon is generally associated with displacement. The normal anti-mesenteric vessels of the cecum can be used to trace its course. Ventral displacement of the spleen with obscuring of the left kidney is associated with nephro-splenic displacement. Visualization of sacculated large bowel immediately ventral to the liver or spleen, or non-sacculated large bowel in the ventral abdomen suggests displacement. The stomach can be evaluated for distension and abnormalities of the wall. Abdominal ultrasound is useful in detecting diaphragmatic or inguinal herniation. Abnormalities of the liver or kidneys, both potential causes of false colic, are often detectable with ultrasound.