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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Rotation of the large colon about the mesocolic axis in a dorsomedial or dorsolateral direction
  • Most commonly located adjacent to the cecal base (less commonly involves the sternal and diaphragmatic flexures)
  • Transverse colon or cecum may also be involved
  • Most torsions are in an anticlockwise/dorsomedial direction
  • Rotation of 90–270° will cause partial obstruction of lumen and passage of ingesta
  • Rotation of 270–360° results in complete obstruction, and torsions ≥360° result in strangulating obstruction of the colon

Pathophysiology!!navigator!!

  • Volvulus causes varying degrees of mechanical bowel obstruction which decreases normal colonic absorption and results in electrolyte imbalances and hypomotility, which in turn may contribute to further twisting of the colon
  • Strangulation of the large colon is typically hemorrhagic rather than ischemic, i.e. venous drainage of the colon is compromised but arterial inflow is relatively intact
  • With venous obstruction, blood eventually extravasates into the submucosa and colonic lumen. This causes the colonic epithelium to slough, and these phenomena produce increased gas and fluid accumulation within the colonic lumen
  • Vascular damage results in degeneration of blood vessels and intraluminal hemorrhage
  • With damage to the bowel wall, bacteria and endotoxins, as well as fluid and protein, leak into the peritoneal cavity, which results in endotoxemia, hypovolemia, and hypoproteinemia. Within 4–5 h, the colonic mucosa undergoes complete necrosis
  • Severe systemic shock leads to cardiovascular collapse and death
  • With complete arterial and venous obstruction, tissue perfusion decreases, with resultant hypoxia and ischemia that cause reduced absorption and hypomotility. Prolonged ischemia causes bowel necrosis, with leakage of bacteria and endotoxins into the peritoneal cavity
  • Endotoxemia and hypovolemia result in severe systemic shock, cardiovascular collapse, and death

Systems Affected!!navigator!!

  • GI
  • Cardiovascular

Genetics!!navigator!!

No known genetic basis.

Incidence/Prevalence!!navigator!!

  • Of horses that actually undergo surgical treatment for colic, 10–25% have large colon volvulus. 1 study reported 65% of horses undergoing surgery having a strangulating (>360°) volvulus
  • Prevalence is increased in geographic areas that have a high population of broodmares

Signalment!!navigator!!

Mature horses, especially broodmares in the postparturient period, are more commonly affected.

Signs!!navigator!!

Historical Findings

History is reflective of how quickly and how fully a complete volvulus (i.e. >360°) occurs. Can be a chronic colic that suddenly worsens, or a sudden onset of severe abdominal pain.

Physical Examination Findings

  • If large colon volvulus is strangulating, horses show severe uncontrollable abdominal pain
  • Initially horses may have normal cardiovascular parameters, and rectal palpation can be unremarkable. As the condition progresses these parameters deteriorate. A heart rate >80 bpm is associated with poor survival
  • Amount of gastric reflux depends on the degree of compression of the small intestine by the distended large colon
  • Abdominal distention may be seen
  • Normal gut sounds are reduced or absent in all GI quadrants
  • Signs of shock become rapidly evident

Causes!!navigator!!

  • Exact cause is unknown
  • Hypomotility and increased intraluminal gas accumulation are thought to initiate a rotation of the colon. Nonstrangulating obstructions may progress to strangulating obstructions by this mechanism
  • Horses undergoing a sudden dietary change may be predisposed to increased gas production and altered GI motility
  • Postparturient broodmares are thought to be predisposed because of increased space within the abdomen

Risk Factors!!navigator!!

  • Foaling within the past 90 days
  • Change of feeding practice
  • Feeding sugar beet
  • A recent increase in the number of hours of stabling

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Nonstrangulating obstruction—torsion <360°
  • Other abnormalities involving the large colon, including right or left dorsal colon displacement, impaction, tympany, enterolithiasis
  • Other acute abdominal accidents—including those affecting the cecum, small intestine, stomach, and small colon

CBC/Biochemistry/Urinalysis!!navigator!!

  • A high packed cell volume (>50%) is associated with a poor prognosis, as is a low total protein
  • Nonspecific hematologic changes such as leukopenia, neutropenia, with or without a left shift, lymphopenia, and thrombocytopenia are reflective of inflammation and/or endotoxemia
  • Elevated lactate may reflect ischemic injury and a value of >6 mmol/L has been associated with a poor prognosis for survival in horses with large colon volvulus
  • A metabolic acidosis may be apparent on venous blood gas analysis
  • On urinalysis, isosthenuria, glucosuria, proteinuria, and casts or red blood cells may occur from prerenal or renal azotemia, caused by hypovolemia and shock

Other Laboratory Tests!!navigator!!

Elevated protein concentration and lactate in the peritoneal fluid are useful indicators of a strangulating obstruction of the large colon. Visual assessment of peritoneal fluid is also useful—a turbid, red to brown appearance is indicative of a strangulating lesion.

Imaging!!navigator!!

  • Ultrasonography is useful. The dorsal colon can be imaged in the ventral abdomen if a 180° or 540° volvulus is present
  • A colonic wall thickness of >9 mm is suggestive of a large colon volvulus

Other Diagnostic Procedures!!navigator!!

  • Nasogastric intubation is a necessary part of all colic examinations
  • Rectal examination can be challenging in the severely painful horse and it is not always possible to complete a full examination. Chemical and physical restraint can facilitate the procedure
  • Findings at rectal examination will vary depending on the progression of the volvulus
  • Distended large colon and tight colonic bands can be palpated further on in the progression, and edema of the colon may be evident
  • Sometimes, gas distention in the colon is so severe that a complete rectal examination cannot be performed

Pathologic Findings!!navigator!!

  • The location and degree of the volvulus can be identified during surgery or at postmortem evaluation
  • The level of devitalization of the large colon is dependent on the location and degree of the volvulus, and the duration

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Physical examination, nasogastric intubation, and rectal examination should be performed
  • Surgery is necessary for chance of a successful outcome
  • Rapid referral for surgery is of paramount importance for increasing the chance of survival
  • Pain medication including flunixin meglumine, α2-agonists and opioids may be required
  • Withhold feed preoperatively

Nursing Care!!navigator!!

Refer affected horses to a surgical facility immediately after initial diagnosis.

Activity!!navigator!!

  • In the 4 weeks following surgery, stall rest with hand-walking daily is advised
  • Following this time, horses can be turned out into a small paddock for limited exercise for a further 4 weeks
  • A gradual return to exercise over weeks 9–12 following surgery is recommended

Diet!!navigator!!

  • Fasting prior to surgery
  • Gradual feed reintroduction in the postoperative period

Client Education!!navigator!!

  • Inform clients that prompt diagnosis and early surgical intervention are very important in the outcome for survival. A survival advantage is seen in horses with a colic duration of <2 h before surgical intervention
  • Complications following surgery may affect outcome, including colic, ileus, peritonitis, incisional infection, jugular thrombophlebitis, and diarrhea
  • 1 paper reports a recurrence of 5%
  • Pregnant mares may abort

Surgical Considerations!!navigator!!

  • Surgical correction is performed via exploratory laparotomy
  • Some surgeons advocate resection to prevent recurrence. The decision-making process for resection is complex. Removing the majority of diseased colon may reduce endotoxemia. However, the procedure has risks of complication and, depending on the location of the volvulus, it may not be possible to remove all of the diseased portion
  • A colopexy technique is not often performed.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Administer flunixin meglumine
  • Further analgesics including α2-agonists and opioids may be administered if necessary

Contraindications!!navigator!!

As described for other causes of colic.

Precautions!!navigator!!

  • Deterioration in condition may be difficult to detect if repeated administration of analgesics
  • Repeated dosing of long-acting α2-agonists may affect cardiovascular hemodynamics

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Horses are usually hospitalized for up to 1–2 weeks following surgery, depending on occurrence of postoperative complications
  • Once discharged from the hospital, routine daily monitoring should be performed

Prevention/Avoidance!!navigator!!

  • Employ feeding practices that avoid large quantities of lush pasture, large amounts of grain, and sugar beet wherever possible
  • Make all dietary changes gradually over a period of several days
  • Allow as much turnout as possible because increased stabling may be a risk factor
  • Provide dental care to prevent quidding
  • Resection or colopexy of the large colon can prevent recurrence

Possible Complications!!navigator!!

  • Large colon necrosis and rupture may occur preoperatively as a result of the rapid progression of the disease
  • Similarly, large colon rupture may occur intraoperatively as the volvulus is corrected
  • Anesthetic death is possible as of result of the compromised preoperative cardiovascular status
  • Complications following surgery may affect outcome, including ileus, peritonitis, incisional infection, jugular thrombophlebitis, and diarrhea

Expected Course and Prognosis!!navigator!!

  • Surgery is required for strangulating volvulus. Without surgery, the horse will die
  • >19–33% of horses with strangulating volvulus do not recover from anesthesia due to the severity of lesions
  • Reported short-term (i.e. discharge from hospital) survival rates following surgery vary from 35% to 88%. Prognosis is improved substantially by early referral and prompt surgical treatment. Long-term survival may be low compared with other causes of colic treated surgically

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Endotoxemia

Age-Related Factors!!navigator!!

N/A

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

  • Broodmares that have foaled within the past 90 days appear to be at increased risk
  • The combination of endotoxemia, hypovolemia, general anesthesia, and surgery all pose a risk to the viability of the fetus

Synonyms!!navigator!!

Large colon torsion.

Abbreviations!!navigator!!

GI = gastrointestinal

Suggested Reading ⬆ ⬇

Hackett ES, Embertson RM, Hopper SA, et al. Duration of disease influences survival to discharge of Thoroughbred mares with surgically treated large colon volvulus. Equine Vet J 2015;47:650–654.

Author(s) ⬆ ⬇

Author: Nicola C. Cribb

Consulting Editors: Henry Stämpfli and Olimpo Oliver-Espinosa

Additional Further Reading ⬆

Click here for Additional Further Reading