Colic is not a specific disease, rather a clinical sign. Colic simply describes abdominal pain and it could originate from a wide variety of sources. Most of the time it originates in the stomach or intestinal tract, but the pain could also arise from other regions, including the kidneys, genital tract, liver, pancreas, or the peritoneum.
There are a number of methods used to assess a horse with colic. A good technique for veterinarians and nurses follows the 10 “P”s and an “I” method. The order of assessment is important.
- Pain
- Paunch
- Pulse
- Perfusion
- Peristalsis
- Percussion
- Pass a nasogastric tube
- Palpation per rectum
- PCV/TP/Lactate
- Peritoneal fluid
- Imaging
1. Pain
The severity of colic signs are highly variable and include anything from laying down (recumbency), abdominal stretching as if posturing to pass urine, teeth grinding (bruxism), arching of the neck, flank watching or biting, pawing, kicking at the abdomen, rolling, posturing to lay down but not doing so, seating, and violently throwing themselves to the ground.
Important things to consider are the duration of the signs of colic, the persistence of signs, the severity of signs and what is the response to analgesics.
2. Paunch
Strictly speaking Paunch refers to large or protruding belly. Overt abdominal distention of the dorsal abdomen in a colicky horse is almost always due to over-inflation of the caecum and large intestine. Distention of the upper right flank is typically due to caecal over-inflation, whereas distention of the left flank could be due to left dorsal displacement of the large colon (nephrosplenic entrapement). Distention of the ventral abdomen is often due to fluid accumulation within the abdominal cavity. The fluid could be blood (hemoabdomen), urine (uroabdomen), lymph fluid (chyloabdomen), or an inflammatory exudate (peritonitis). Gas can be identified using percussion (see “P” 6).
Horses with gastric and/or small intestinal distention rarely have any change in body shape. This is different in young foals.
The next 2 P’s involve initial assessment of the head. These two parameters, in conjunction with Pain and Paunch can provide substantial insight into whether the underlying condition is strangulating or non-strangulating, or anatomically based in the small intestine or large intestine.
3. Pulse
Pulse rate is one of the most important aspects of the evaluation. Rate needs to be evaluated in context of severity of pain, analgesics (alpha-2 agonists cause a reflex bradycardia), integrity of circulation, excitement, and breed. The influence of circulatory shock on heart rate is very important, and is further assessed by mucous membrane colour (P no 4), packed cell volume, lactate (P no 9), and creatinine. A pulse rate between 40 and 60 bpm usually reflects mild abdominal pain and is most consistent with obstructive disease of the large intestine. Persistent rates of 60 to 80 bpm frequently indicate more severe underlying disease, and rates above 80 bpm are often due to strangulating lesions of the small or large intestine. It is important not to use rate as the sole determinant for surgery, although it remains one of the most important guides. High pulse rates in the absence of abdominal pain could be indicative of an arrhythmia, such as atrial tachycardia or ventricular tachycardia.
4. Perfusion
Hemodynamics is reflected by mucous membrane colour and dryness, and capillary refill time (CRT). Simple dehydration (<5% loss of bodyweight) results in dryness of the membranes. Deterioration in circulatory status often occurs as a consequence to toxaemia; membrane colour initially changes from light pink to dark pink, then to a light purple colour, and then dark or “brick” red. CRT typically prolongs as the membranes darken; CRT times beyond 4 seconds are indicative of circulatory collapse. There may be a contrasting discolouration around the gingival margins, referred to as a “toxic” line, due to the close association with clinical endotoxemia. Extremities (distal limbs, ears) are often cool to the touch and the jugular refill time (JRT) is delayed (>3 seconds) with hypovolaemia. Additionally, pulse quality will reduce and pulse rate increase with advancing hypovolaemia.
The next 2 “P”s incorporate auscultation and percussion of the abdomen
5. Peristalsis
Intestinal sounds (borborygmi) are assessed in 4 quadrants (left dorsal and ventral, and right dorsal and ventral). It is important to listen for at least 20 seconds in each region. In some places vet students and nurses are asked to grade duration, intensity and frequency in each area. This is a complex system and many prefer to assess with 0 (no sounds), 1+ (present but reduced sounds), 2+ (normal), and 3+ (increased sounds). It is difficult to separate large intestinal sounds from small intestinal sounds. The exception is the right dorsal quadrant which focuses on the caecum. The two commonly heard sounds in this region are a high pitched “tinkle”, caused by the terminal small intestine (ileum) injecting chyme into the gas filled caecal base (cupula), and low long low frequency rumble, thought to be caused by caecal contents into the right ventral colon. Some have described this sound as a “toilet flush”.
Intestinal sounds are usually decreased in most horses with colic. It is important to interpret sounds in light of drug usage, e.g., xylazine or detomidine will decrease hindgut activity (and therefore gut sounds) for 30-40 minutes, and recent feed intake.
Increased sounds are associated with condition of “spasmodic colic”. The pathophysiology of this condition is not known, but could involve mucosal irritation due to ingestion of legume pastures. Increased sounds are also commonly seen in hoses with colitis, but sounds are often reduced to absent in the early stages of disease.
Specific sounds associated with sand movement can be auscultated on the ventral abdomen caudal to the xiphoid process. The sounds are reminiscent of rumen sounds or the sound of sand in a bag that is slowly rotated. It can sound like a long wave breaking on a beach with a slow crescendo and then decrescendo.
6. Percussion
The technique involves simultaneous auscultation and striking or flicking of the abdomen with the index or middle finger. The resonance of the sound reflects the underlying tissues. High pitched or hollow pings indicate the presence of a gas-filled viscus, usually caecum or large colon.
7. Pass a nasogastric tube
Therapeutic tool – this is an important procedure in animals with moderate to severe pain, as gastric distention is a frequent source of severe colic. If more than 5 liters of net reflux is retrieved from the horse then it is advisable to leave the tube in place. Cap the end with a syringe or syringe case, tape tube to the halter, and apply a plastic muzzle to prevent the horse from removing the tube. This is particularly important if the horse is to travel to a hospital facility.
Diagnostic tool – the retrieval of a large volume of net gastric reflux (>5 litres) usually suggests a primary gastric or small intestinal problem. Large colon diseases can lead to a reduction in gastric emptying due to extra-luminal compression of the duodenum. The volume itself does not indicate whether or not surgery is required, but high volumes with moderate to severe pain that is not alleviated by removal of fluid supports a diagnosis of strangulating small intestinal disease. Diseases with potential medical therapies that result in high volume reflux include duodenitis proximal jejunitis (DPJ), post-operative ileus (POI), and ileal impaction.
8. Palpation per rectum
Rectal palpation is a critical test in evaluating the colicky horse, particularly in those where a decision for surgery and euthanasia is required. It is important to consider both your own safety and that of the horse. Consequently, the decision to perform a rectal examination in the field should not be taken lightly. Most colics are not rectally palpated on the initial visit – remembering that the majority of colic cases in Western Australia are caused by intra-luminal obstruction of the large colon with either sand or feed.
Specific diagnoses, such as colonic or caecal impaction, large colon displacements, or enteroliths, can often be established on rectal examination. The technique is useful for differentiating small intestinal and large intestinal diseases. Small intestine is not typically palpated per rectum in the normal horse.
Sand test: Place handful of faeces into a rectal sleeve and add water, mix, and allow to stand. Examine fingertips for sedimentation of sand.
Parasites: Examination your rectal sleeve and faeces for evidence of adult roundworms, tapeworms or strongyle larvae. The latter appear as tiny red worms.
9. Packed cell volume, total protein and lactate
Requires a microhematocrit centrifuge and handheld refractometer – consequently this test is almost always reserved for a referral hospital setting. Aids in assessment of hydration and degree of endotoxemic shock. Total protein is more reflective of hydration than PCV, but assumes a normal baseline value. Progressive shock is usually associated with a rising PCV and a falling total plasma protein concentration. A PCV > 0.55 with a protein < 5.5 gm/L would be indicative of such a state. PCV (as a percent value) multiplied by HR has been suggested as a sound indicator of outcome (cut-off quoted as 4000). Lactate elevates in peripheral blood in response to altered perfusion. It is most commonly elevated (> 6-8 mmol/L) when there is long-standing strangulation (e.g., colonic volvulus) and predicts a poor outcome. Lactate is normally less than 2.5 mmol/L.
10. Peritoneal fluid
Peritoneal fluid is a critical sample in a small number of colics. This technique is rarely performed on the typical field colic case. It is particularly important in differentiating strangulating from non-strangulating lesions. It is also very important in confirming intestinal rupture, but be careful, as some can be falsely condemned on the basis of inadvertent enterocentesis. It is also possible to contact the spleen resulting in dark blood being sampled.
Peritoneal fluid lactate (PFL) concentrations are more useful and sensitive than peripheral blood lactate for determining the prognosis in colicky horses.
Imaging
Imaging can be an extremely important tool in the evaluation of colicky horses. Ultrasound is the modality of choice, although some training is required for accurate interpretation. It is also helpful in identifying pockets of peritoneal fluid for sampling, determining small intestinal size and motility, intestinal wall thickness, and assessing the stomach size.
Tags: Gastrointestinal diseases