When field veterinarians are evaluating a horse suffering from colic, the most important question to quickly answer is, “Does this horse need surgery, or can the issue be resolved through medical treatment?” An evidence-based approach to evaluating the usefulness of the information gathered during the clinical exam can help equine veterinarians make an appropriate decision.
Many horses referred to hospitals for colic surgery are presented with severe gastrointestinal lesions that can quickly lead to shock and death. The survival rate rapidly decreases in inverse proportion to the duration of clinical signs. The more quickly a horse is referred to surgery, the more likely the horse will have a successful surgical outcome.
Thus, it is incumbent on veterinarians sending horses to hospitals for potential colic surgery that such referrals are made as quickly as possible.
One method of facilitating early surgery would be to refer all horses with colic to a referral clinic. However, such a practice would surely be economically burdensome on clients. While no single diagnostic test has been shown to predict the need for surgical colic with 100 percent accuracy, certain tests appear to be strongly predictive of the need for surgery.
Note Any Pain
The intensity of pain is one of the most important variables in discriminating between surgical and medical cases. This relationship appears to be linear—that is, the more severe the colic pain, the more likely surgical correction will be needed.
Check Body Temperature
Changes in a horse’s body temperature may be caused by many factors, including pain and local or systemic infection. While colic may be accompanied by a rise in body temperature, at least one analysis concludes there is an inverse association between temperature and the need for surgical intervention. Fever typically accompanies peritonitis, however, and the prognosis for survival can be quite poor, especially if a ruptured viscous is present, even with surgery.
Look for Abdominal Distension
Visual evidence of marked abdominal distension helps identify horses with colic that need surgical referral. However, determining abdominal distension is somewhat subjective. Thus, it is somewhat difficult to make specific recommendations for a general population of horses based on this variable.
Listen to Abdominal Sounds
A decrease, or absence, of intestinal sounds has been associated with a need for surgery. Studies have indicated that as many as 50 percent of horses with colic that ultimately needed surgery had absent gut sounds. Of course, this also means that 50 percent of the horses that needed surgery had gut sounds. Clearly, the absence of gut sounds should be interpreted in light of other factors.
Examine Peritoneal Fluid
Abdominal fluid color and protein can help predict the need for colic surgery. These variables are easily measured in the field, and they provide immediate information without the need for sophisticated laboratory techniques. In cases of surgical colic, peritoneal fluid may become darker and protein levels may increase. This relationship is consistently linear—the darker the color, the more likely a horse needs surgery.
Nevertheless, results of abdominal fluid analysis should not be used alone. For example, peritoneal fluid hemolysis can make interpretation of peritoneal fluid confusing. Peritoneal fluid characteristics do not appear to be useful in predicting outcomes for horses with colic.
In general, peritoneal fluid color and protein appear to have a greater negative predictive value than a positive predictive value. Unfortunately, peritoneal fluid cannot always be obtained.
Know Cardiovascular Variables
Variables pertaining to the cardiovascular system are associated with both the prognosis and treatment. A weak peripheral pulse may increase the risk that surgery is necessary, but this parameter is quite subjective. The probability that surgical treatment is necessary increases when high-packed cell volumes are present.
Mucous membrane color appears to be a fairly poor predictor of the need for surgery at first examination. Heart rate appears to be correlated with the need for surgery in a linear fashion—that is, the higher the heart rate, the more likely surgery will be required. Survivors of colic surgery tend to have significantly lower heart rates than do horses that ultimately do not overcome colic. Blood pressure and blood lactate concentrations do not appear to be good predictors of the need for surgery.
Notice Analgesic Response
The lack of response to alpha-2 agonist analgesic administration (e.g., xylazine, detomodine), or the rapid resumption of colic signs following such medication, should be considered a positive indicator of the need for surgery. However, the presence of constant pain after analgesic administration does not always indicate a need for surgery.
On the other hand, the response to analgesic administration appears to have significant negative predictive value. If a horse responds to analgesic treatment and pain does not subsequently return, surgery is likely not to be indicated.
Perform Rectal Examination
In general, scientific literature supports the diagnostic benefits of rectal examinations in horses with colic, but there is considerable variability in the diagnostic benefits.
It is sometimes possible to make specific diagnoses by rectal examination, though rectal examination findings such as intestinal distension or dislocation are nonspecific. While abnormal rectal examination findings do not necessarily increase the risk for surgery, some specific types of colic (e.g., pelvic flexure impaction) may be more accurately diagnosed by rectal examination than others. Since a significant portion of the abdominal cavity cannot be assessed per rectum, rectal examination may be of limited value in some cases. Of course, the procedure has very limited application to small equids, such as miniature horses, some ponies and foals.
Check Nasogastric Reflux
Reflux from the stomach upon passage of a nasogastric tube is of variable significance in predicting the need for colic surgery and can occur in both medical and surgical cases. The presence of nasogastric reflux in horses presenting for signs of colic must be interpreted in light of other clinical features.
Ultrasonographic evaluation of the abdomen appears to be very useful in helping to determine whether a case is likely to be a surgical candidate. A sensitivity and specificity of abdominal ultrasonography of 100 percent, respectively, has been reported in cases of horses with acute abdominal pain.
Ultrasonography is also a practical and reliable method of detecting sand accumulations, although smaller and more dorsally located accumulations may be difficult to detect.
Ultrasonographic findings may aid in the earlier diagnosis of large colon volvulus in horses, especially at an early stage of the disease when other clinical signs are equivocal.
Time for Surgery?
The surgical predictive value of various diagnostic tests used to evaluate colic patients
Strong Positive Predictive Value
- Response to alpha-2 agonist analgesia
- Abdominal ultrasonography
- Degree of pain
- Abdominal fluid color
- Adominal fluid protein increase
- Abdominal distension
- High PCV
- Elevated heart rate
Strong Negative Predictive Value
- Rectal examination
- Auscultation of the abdominal cavity
- Mucous membrane color
- Blood pressure
- Blood lactate concentration
- Nasogastric reflux
Dr. David W. Ramey is an author, lecturer and Southern California equine practitioner who specializes in the care and treatment of pleasure horses. His website is www.doctorramey.com.
Originally published in the June 2016 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today!