When Gut Attacks - All Ages, All Comers

Take Home Message—Gastrointestinal conditions may be acute or chronic, painful or seemingly benign, have no systemic effects or be responsible for profound losses in condition or performance potential. When acute, establishing a diagnosis, preserving life and controlling pain are first and foremost. When chronic, the management plan may be difficult to formulate and achieve only intermittent success. Clinical findings should be interpreted in relation to the historical information available. Confirming a definitive diagnosis before action is required may not be obtainable.

I. INTRODUCTION

Acute or chronic gastrointestinal pathology is a common and potentially life-threatening affliction of the horse, with the majority of horses suffering from one of these conditions sometime during their lives. The majority of gastrointestinal conditions are amenable to medical management and in some cases this may be chronic in nature, however acutely painful conditions may indicate an intestinal accident is present necessitating surgical intervention.

II. COLIC

The degree of pain shown during a gastrointestinal condition will largely determine the approach to diagnosis and management. The presence of intractable abdominal pain necessitates surgical exploration.

History

Signalment: Geriatric horses may have a similar admission cardiovascular status compared to mature horses (heart rate, packed cell volume, plasma creatinine and blood lactate concentration) but a more serious cause of colic underlying the episode.¹ Increased occurrence of enteroliths in Arabians and miniature breeds has been demonstrated.² 

Management changes and potential triggers: transport, administration of medications for concurrent conditions (antimicrobials, anti-inflammatories), and changes in social structure by the addition or removal of other horses may precipitate colic. More frequently, recent feed or water changes may be incriminated.

Pattern of colic episode(s): How often and over what time period has the colic been apparent (isolated episode versus chronic intermittent over months)? Are episodes similar or signs random? Is there a temporal relationship to estrous cyclic activity (actual or perceived)?

Fecal production: Decrease in volume or frequency of fecal production is suggestive of decreased dietary intake (inappetence, inability to prehend food, competition), or prolonged intestinal passage (motility disorders, obstructive processes, increased fecal density).

Pain

Duration: The duration of signs of colic prior to evaluation has been associated with survival.³ 

Severity and frequency: In many prognostic models, the degree of pain affects survival.^4,5 Horses vary in their pain responses, so it is useful to know if this episode is consistent with other colic episodes (is it more or less severe?)

Response to analgesics: What is the duration and completeness of response to analgesics? Alpha-2 adrenergic agonists have a rapid onset and may provide visceral analgesia for prolonged periods.⁶ Flunixin meglumine has been shown to provide less visceral analgesia.⁶ 

Clinical Examination

In one referral center colic study, there was a significant association between predicted survival and outcome based on clinical impression, and this correlation improved with increased case exposure.⁷ 

Vital signs: Rectal temperature is widely variable, ranging from elevated with acute infectious involvement to hypothermic in the presence of severe hypovolemia or devitalized bowel. Cardiovascular parameters are significant predictors of mortality in multiple studies.^8-10 Heart rate is variably elevated (individual pain tolerance) and alone cannot be relied upon to predict outcome.⁸ Hypovolemia may be responsible (are signs of circulatory compromise present?). Paradoxically, a normal heart rate may be present with significant gastrointestinal compromise. Pulse quality can be assessed peripherally at the distal extremities or the facial artery along the mandible. Poor pulse pressure is suggestive of endotoxic shock, hypovolemia or cardiac compromise.¹¹ A bounding pulse indicates the early stages of endotoxemia before decompensation occurs. Respiratory rate and effort when elevated may indicate pain, acid-base disturbances, physical impediment to the diaphragmatic excursion due to visceral dilation or pleural space disease (pleural pain can mimic gastrointestinal pain).

Mucous membranes: Color is anecdotally considered a reliable prognostic indicator, with some^8,12 but not all retrospective studies agreeing.³ Capillary refill time was not shown a reliable indicator of the need for medical or surgical management in one study.¹³ However, a shorter capillary refill time was associated with increased likelihood of survival.^12,14

Abdominal size: Abdominal distension, rectal findings and peritoneal fluid color were the most discriminating deciding variables between medical and surgical management in one study.¹⁵ In another study, rectal examination findings, abdominal fluid composition, presence of intractable pain, and abdominal distention were most likely to differentiate between medical and surgical lesions.¹⁶

Abdominal sounds: Increased gut activity is seen in conditions which irritate the intestinal tract. Decreased or absent gut activity may indicate a more serious situation, with decreased fecal production and signs of acute pain indicating a less favorable prognosis. Decreased borborygmi may also indicate sudden feed changes, carbohydrate overload, or infectious agents.

Oral examination: Decreased frequency of dental examinations and treatments are associated with increased risk of colonic distention and impaction.¹⁷

Trauma signs: Duration and severity of unobserved pain may be indicated by skin abrasions, musculoskeletal injuries and damage to housing.

Nasogastric Intubation

Character and amount of nasogastric reflux, and the response of the horse to passage of the fluid yields valuable information. Amount, timing relative to the occurrence of colic, and character of reflux should be noted. A small intestinal problem is implied by the presence of significant amounts of fluid. When obstructed, the proximal small intestine yields a high volume of reflux. Duodenitis-proximal jejunitis (anterior enteritis) yields malodorous, sometimes hemorrhagic fluid. Lower small intestinal lesions are much less likely to reflux initially. Physical obstructions yield relatively fresh feed and intestinal fluids. Colonic distension may cause reflux by duodenal compression. Small intestinal ileus will experience a relief of pain and a decrease in heart rate with gastric decompression. Physical obstructive lesions are most likely to have no response to successful reflux.

Rectal Examination

Intestinal distension and disposition prompts categorization of diagnosis.^10,18 Rectal examination has been reported as the single most useful pre-surgical diagnostic tool, allowing definitive diagnosis of many large intestinal conditions and providing non-specific information about small intestinal disease. Serosal surfaces are able to be felt and character assessed for signs of peritonitis. Fecal presence or absence and consistency can be evaluated. The spleen, left kidney and uterus can be assessed.

Concurrent Conditions

Fecal consistency gives insight to nutritional imbalances, the presence of infectious enteric agents, or changes in fecal density. Infectious and inflammatory conditions within the peritoneal cavity can produce signs consistent with an intestinal lesion. Pain similar to a colic episode can result from rhabdomyolysis, pneumonia, pleuritis, nephritis, nephrolithiasis, and cholelithiasis.

Ancillary Aids

Ultrasonography: Rapid assessment of intestinal wall thickness, diameter, content and motility, stomach size, quantity and nature of peritoneal fluid, and position of the viscera and intestinal tract is possible. Comparing surgical and necropsy findings, ultrasonographic detection of abnormal small intestine that lacked motility was highly sensitive and specific, with high positive and negative predictive values for small-intestine strangulation.¹⁹ With large colon lesions, imaging via a ventral abdominal window was moderately sensitive and highly specific for diagnosis of large-colon torsion.²⁰

Peritoneal fluid: In the field, it is challenging to gain all the information contained in a sample in a timely fashion. Gross appearance is therefore the most valuable indicator of the presence of devitalized gut and is most likely to aid the clinician in the determination of the need for surgery. Normal fluid is clear and pale yellow/straw-colored. It does not clot in a plain tube. Yellow fluid that is slightly turbid suggests a medical colic, with dehydration or elevated bilirubin. Pink/orange fluid indicates hemolysis or hemorrhage. The presence of hemolysis increases the likelihood of the need for surgical correction.¹⁵ Hemolysis may be distinguished from iatrogenic hemorrhage by centrifugation or allowing time to settle as iatrogenic hemorrhage will form a pellet of red cells with a clear supernatant. Compromised vascular supply to the gut, however, will result in fluid that does not settle but instead remains uniformly pink/orange. Bloody to brown fluid indicates advanced ischemia, and the presence of ingesta indicates rupture or enterocentesis has occurred. Increased protein concentrations occur with peritonitis and surgical colic where inflammation and vascular compromise of the gut has occurred. Protein can be readily assessed with a hand-held refractometer. Volume of peritoneal fluid at the time of sample collection can be suggested by the flow rate: since fluid can pocket in the peritoneal cavity this is an unreliable indicator. Serial evaluation of abdominal fluid color and specific gravity has a high positive predictive value for type of intestinal lesion,²¹ whereas patient age and abdominal fluid color has a high positive predictive value for clinical outcome.²¹ [...]