BACK TO BASICS: THE ACUTE ABDOMEN IN THE FIELD


use flunixin meglumine (0.25–1.1 mg/kg, IV), it has a long duration of action (up to 12 hours), which makes it more difficult to determine if colic is recur- rent while conducting a timely visit. Another med- ication that has become available is hyoscine butylbromidea (0.3 mg/kg, slowly IV). This is an excellent anti-spasmodic agent, but the product sold in the United States does not contain an anal- gesic (this product sold in Europe, also contains dipyrone [metamizole] and is the favored choice for initial treatment for colic in other countries). How- ever, hyoscine butylbromidea can be given with non- steroidal anti-inflammatory drugs available in the United States. Concerns on transient elevations in heart rate with hyoscine butylbromidea (approxi- mately 20 minutes) become of less concern if the veterinarian has already checked the heart rate and administered an analgesic. If an initial dose of xy- lazine, particularly if administered with butorpha- nol, has no effect, the treatment can be repeated. However, it is important to realize that the necessity for a second treatment with an analgesic raises the index of suspicion that a horse needs referral. If pain continues, more potent sedatives such as deto- midine (0.01–0.02 mg/kg; 5–10 mg, IV) can be used and can be repeated as needed if the horse remains painful. If repeated doses of detomidine are inef- fective, the horse needs to be referred if at all pos- sible. For owners that do not wish to refer, inability to control pain is an important factor in making the decision to euthanize a horse. Alterna- tively, for horses that respond well to an initial dose of xylazine, following completion of the remainder of the examination, flunixin meglumine (1.1 mg/kg, IV) is helpful as an anti-inflammatory and longer dura- tion analgesic if it has not already been given. If colic does recur, the risk that surgery or intensive care is needed is increased. Therefore, the owner or trainer should be given explicit instructions to keep the horse in a stall, hold the horse off feed, and regularly monitor the horse for 24 hours for recur- rence of pain. It is also helpful to ask the owner to assess fecal output. Many horses that arrive at referral hospitals after prolonged durations of colic have been treated on multiple occasions for colic, which can be improved upon if horses with the first recurrence of pain after analgesia are considered for referral. Nonetheless, considerations of expense, owner preference, and shipping are widely under- stood to complicate decision making.


6. Remainder of the Physical Examination


Once the horse is comfortable, the level of dehydra- tion can be determined by tenting the skin on the neck, and looking at the appearance of the eye in the orbit. This can be deceiving in senior horses be- cause of the loss of elasticity of the skin. Nonethe- less, most horses can be practically defined as not dehydrated (skin tent, 2–3 seconds), 6% dehydrated (3–6-second skin tent), 8% dehydrated (6–8 second skin tent, some evidence of the eye sinking back into


the orbit), or 10% dehydrated (prolonged skin tent, obvious sinking of the eye). The next component of the examination is auscultation of the chest to con- firm heart rate (this may be affected by an alpha-2 agonist such as xylazine) and to briefly auscultate the lung fields. Auscultation of the ab- domen at the paralumbar fossa as well as at a site on the lower flank for approximately 1 minute on each side is reasonable to classify gut sounds as absent, normal, or increased. Gut sounds may be reduced in response to alpha-2 agonists. The time required for this part of the examination provides a good opportunity to take the rectal temperature, and this should always be done prior to rectal palpation. A febrile horse with signs of colic is often associated with the early phases of enteritis or colitis, and some horses with colitis have severe abdominal pain. Rectal palpation is a useful and practical means to determine the intestinal segment causing the cause of colic. Determining the position of the spleen is important. If it feels larger than normal, and pushed away from the body wall, the most frequent reason is that the colon is between the spleen and body wall. Phenylephrine (0.01 mg/kg over 20 min- utes diluted in saline) and walking or jogging the horse can be helpful to vasoconstrict the spleen to help resolve possible colonic displacement on the left side of the abdomen.7 Another critical component of the colic examination is nasogastric intubation. When horses have severe pain or tachycardia, the stomach tube should be passed early during the examination to relieve possible gastric distension. Diagnostic ultrasound is becoming a common diagnostic modality and can be adapted to use rap- idly in the field using a fast localized abdominal sonography for horses examination. This takes ap- proximately 10 minutes to perform, and can be used to detect such findings as abdominal fluid, distended small intestine, and the appearance of the nephro- splenic space. This is particularly useful in regions of the abdomen beyond the reach of rectal palpation and can be used in conjunction with rectal palpation to provide as much information as possible in terms of localizing the cause of colic.


7. Laxative Treatment


Laxatives should be administered via nasogastric tube, and only when there is no evidence of gastric reflux. Additionally, if the veterinarian suspects a small intestinal obstruction, including ileal impac- tion, nasogastric laxatives or fluids are not indicated because of a lack of transit to the region of the impaction. If a horse is suspected of having a gas- tric impaction, multiple water lavages of the stom- ach are warranted. Although mineral oil (2 to 4 L/500 kg PO) is commonly used as a laxative, it has been shown that hydration of the colonic contents can be better achieved by administration of magne- sium sulfate (1 g/kg in4Lof water PO).8 While sodium sulphate has been shown to result in greater colonic content hydration than magnesium sul-


AAEP PROCEEDINGS  Vol. 66  2020 117


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