34th Annual Scientific Meeting proceedings

Colic is a major cause of death in horses, and the prognosis for survival increases with early surgical intervention. Much research effort has therefor been made to find factors that can aid in identifying cases needing surgical intervention. Also, a better understanding of the prognosis for survival of an individual horse can help the owner make the decision to agree to a cost intensive surgical treatment of their horse.

Obtaining a case history and performing a thorough physical examination is routinely performed in equine colic patients. However, correctly predicting the need for surgical intervention and the potential for survival is difficult and strongly influenced by the experience of the examiner. Prediction models and decision trees based on these parameters have been developed by several authors. In these, there is a tendency to overestimate the need for surgery, and between 9 and 17 percent of horses that needed surgery where wrongly classified as not needing surgery (1,2,3,4).

In an attempt to improve the predictive values several laboratory parameters have been evaluated. For practical use these parameters should be easily obtainable in a clinical or stall side setting. Both lactate and SAA can be easily measured and these parameters are widely used.

Increases in lactate both in serum and peritoneal fluid have been associated with an increased likelihood of the presence of a strangulating lesion and a decreased likelihood of survival (6). In particular, the ratio of peritoneal to serum lactate can improve diagnosis of ischaemic intestinal lesions (11) and prognosis for survival after surgery (12). Serum lactate may also increase as a result of other causes such as muscular stress in a severely colicing horse, enteritis or systemic inflammatory response syndrome. This can result in potentially high serum lactate levels in horses without a strangulating intestinal lesion, limiting its use in diagnosing surgical lesions.

Serum amyloid A (SAA) was higher in horses suffering from conditions having a primarily inflammatory cause and was higher in non survivors than in survivors (7). However, there was a high variability in SAA between horses, and the authors concluded that the sensitivity and specificity of SAA concentration did not appear to be high enough to be clinically useful. SAA has also been investigated to predict the occurrence of post operative infection, in particular suture site infection. However, SAA was high in all post operative colic horses, probably due to the inflammation induced by the disease and the surgical procedure (5). In another study serum SAA peaked at day 2 after surgery and then declined in horses surviving to discharge after colic surgery, while in horse developing complications or not surviving to discharge it continued to increase at day 4 or 5 post operatively (10).

Since individual laboratory parameters did not appear to be sufficiently reliable in a clinical setting, research has focused on the value of combining clinical and laboratory parameters. Pihl et al. developed a model based on clinical parameters alone to differentiate between horses suffering from severe colic caused by an inflammatory lesion versus those with a lesion requiring surgical intervention (4). Their model could correctly differentiate between inflammatory and surgical lesions in 86% of horses. When adding serum SAA values to this model, it was able to correctly identify the nature of the colic in 90% of the horses. No further blood or peritoneal fluid parameter significantly improved this model. Another colic scoring system combined results from the physical examination (heart rate, respiratory rate, ultrasound exam, rectal exam) with two laboratory parameters (blood lactate, total calcium) to predict survival (13). This model had a positive predictive value for survival of 88% and a negative predictive value of 52%, indicating that 48% of horses the model predicted to die were discharged from the hospital alive.

Other biomarkers have been identified to differ between surgical and non-surgical colic or horses surviving and not surviving, such as various proteins (8) and salivary alpha-amylase (9). Peritoneal fluid procalcitonin was higher in horses with strangulating intestinal lesions than in those with non-strangulating lesions (PPV 56.7%, NPV 87.9%) (14). To date these molecules are not readily determinable in a clinical setting and therefor are limited to research use at this point.

In a clinical setting we are deciding on the fate of one individual horse. While a percentage of horses submitted to surgery that subsequently are diagnosed with non-surgical lesions may be acceptable, very high standards need to be set to classify a horse as unlikely to survive with or without surgery. To date, no model and no parameter has been identified with sufficient predictive values to justify euthanasia based on the model or parameter alone. The experience of the examiner remains an important part in evaluating a colic patient. Repeated evaluations of the horse (before and after surgery) and of selected laboratory parameters can help in evaluating the need for surgery and the prognosis for survival. In doing this, care must be taken to not unnecessarily increase the cost of treatment, because this could limit the number of horses we can treat for colic due to financial restraints of the owner. In our hospital we therefore have a policy that additional diagnostic steps like abdominocentesis or certain laboratory parameters, even abdominal ultrasound, should only be performed if we expect a difference in the way we proceed with the patient.

References

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2. Reeves MJ, Curtis CR, Salman MD, Stashak TS, Reif JS (1991) . Multivariable prediction model for the need for surgery in horses with colic. Am J Vet Res 52:1903–1907.
3. P J Pascoe, N G Ducharme, G R Ducharme, J H Lumsden (1990). A computer-derived protocol using recursive partitioning to aid in estimating prognosis of horses with abdominal pain in referral hospitals. Can J Vet Res 54(3):373-8
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9. Contreras-Aguilar MD, Martinez-Subiela S, et al. (2019). Salivary alpha-amylase activity and concentration in horses with acute abdominal disease: Association with outcome. EqVetJ 51, 569-574.
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14. Kilcoyne I, Nieto JE et al. (2020). Diagnostic value of plasma and peritoneal fluid procalcitonin concentrations in horses with strangulating intestinal lesions. JAVMA 256 (8) 927-933.