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Long term results after equine colic surgery - Where can we improve?
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Summary
Key consideration for improving long term results after colic surgery are time for the initial referral to occur, decisive decision making in the pre- and intra-operative period, and an understanding of the long term complications that can most interfere with optimal long-term outcome. Interestingly, the ultimate target for improving long-term outcome is likely to be a continued effort at shortening referral time, such as by reducing analgesic use by owners, increased use of short duration analgesics, and increased insurance coverage of horses. Too many horses continue to arrive at surgical hospitals with severe lesions in a state of endotoxemia that can be very difficult to manage, and reduces long term results even if the horse can be discharged from the hospital. Once in surgery, avoidance of excessive trauma to both the intestine and incision can avoid problematic long-term complications, namely adhesions and incisional hernias respectively. Other important postoperative complications that can limit long term results are shock states and postoperative ileus. These conditions lack large and rigorous randomized clinical trials to know what is optimal for treatment, and this is clearly one of the factors veterinary surgeons should begin to perform to fully understand outcome. For example, although it is known that lidocaine improves small intestinal mucosal repair, and appears to have a beneficial effect in a small clinical trial, larger clinical trials are needed to determine if this relatively intensive treatment is really effective at improving long term results. Other drugs that are commonly used, such as antibiotics and anti-inflammatory drugs should also be rigorously tested with clinical trials so that a state-of-the-art treatment protocol for postoperative colic patients can be developed on an international basis. In addition, an understanding of the owners expectations can lead to a better definition of long term results. If the expectation is to save the horse’s life, this makes some complications such as incisional hernias a less pressing concern, and even low level chronic laminitis can be managed. However, these same complications are highly problematic and reduce long term results in horses intended to return to athletic performance.
Key Words: Postoperative ileus, adhesions, flunixin meglumine, COX-2 inhibitor
Referral time
When talking about long term results, the obvious place to improve would seem to be surgical techniques or management of postoperative complications, with are critical. However, the universal problem colic surgeons are dealing with is really referral time. Studies have shown that even the most fatal forms of colic, such as large colon volvulus, can be a remarkably positive long term outcome if they are referred rapidly.(1) The study in question is from a referral area that is unique in the Unites States (Lexington Kentucky), in that the value of the horses, the quality of the management, and the proximity to the referral hospital reduces referral time down to a minimum. Even in other similar areas in the US, such as Ocala Florida, the prognosis for large colon volvulus is notably lower, largely because of referral time.(2, 3) It is therefore ultimately the case that equine veterinarians have to work relentlessly on early referral to improve long term results. It is getting to the point where surgical management is rapid, technically proficient, and highly successful. Similarly, with short term survival (discharge from the hospital), result are progressively increasing into the range of 80-90% even with severe conditions like small intestinal strangulating obstruction.(4, 5) However, there is only so much that can be overcome in veterinary medicine when a patient arrives at the Hospital in poor condition. The principal method to reduce referral time, in my opinion, is to encourage use of short-term analgesics. Although the non-steroidal anti-inflammatory drugs, including flunixin meglumine, are highly effective analgesics in horses with colic, they have a longer half-life than drugs such as xylazine and butorphanol. Therefore, an approach that includes an initial small dose of xylazine (0.3mg/kg, IV, prn) to assess whether or not the horse is going to have recurrent pain are very useful. For any horses that does have recurrent pain, this is then an immediate candidate for referral consideration. The owner might decline because of cost, and it is also the case that most cases of colic that are referred can be treated medically. However, to optimize survival for those patients that are surgical, referring after an episode of recurrent pain is optimal. Other important considerations are the degree to which owners are allowed to treat colic by themselves with analgesics provided by the veterinarian (minimal is obviously better), and insurance of the horse (to ease financial decisions).
Colic surgery
Once a horse has been referred, time is again of the essence to make a decision on whether or not a horse should go to surgery in order to improve long-term outcome. Some simple rules apply here. If a horse’s pain is unmanageable, it is a surgical candidate and does not need an extensive examination. Aside from recurrently painful horses, an examination lasting about 30-40-minutes is ideal, to include all components of a physical exam, bloodwork, rectal examination, ultrasonic evaluation, and passage of a nasogastric tube. An abdominocentesis is most helpful in those horses suspected of having small intestinal disease – it is a far less reliable indicator of intestinal injury in horses with acute large colon conditions. Once in surgery, the surgical team should be able to move swiftly through an exploratory and any surgical manipulations required within 2-hours. This should aim to maximally reduce time in the abdomen, which translates to trauma, systemic inflammation, and a poorer long term outcome. Of all of the long-term complications hindering a good long term outcome, adhesions are amongst the most problematic. These result both from the level of intestinal injury present (dependent on duration of disease) and the level of manipulation at surgery. Rapid decision making is needed at surgery in an attempt to reduce surgical time. One aspect of colic surgery that is critical to long-term outcome is closure of the incision. That is because in one study, one of the factors that limited long-term outcome to the greatest extent was abdominal hernias.(6) These likely relate to closure technique, and whether or not the incision becomes infected. Infection rates tend to be in the 10-15% range at most surgical hospitals,(7) but should be monitored closely to make sure the prevalence is not increasing. If it does increase, a serious evaluation of all aspects of the surgical preparation of the abdomen should be evaluated, including culture of clippers, scrub containers, and surgeons hands. An additional factor that likely plays into incisional complications is trauma to the incision, which again relates to time and technical proficiency of the surgical team.
Postoperative complications
There are generally three major complications that I mention to owners following surgery, that correspond to three phases of the postoperative care. Firstly, assuming the horse recovers reasonably well from anesthesia, there is management of shock states (endotoxemia, sepsis, or systemic inflammatory response syndrome). This includes optimal fluid and electrolyte administration, judicious use of non-steroidal anti-inflammatory drugs, use of pain medications to optimize recovery,(8) and use of colloids or plasma as needed to maintain oncotic pressure. Medications to specially target endotoxemia, such as polymixin, may be helpful. The problem is that the very large majority of drugs that are used, even including antibiotics, have not been subjected to rigorous clinical trials, so we can only rely on the general standard of care established by practice and not on evidence. This is a clear area of improvement that can affect long-term outcome. The next phase of postoperative management tends to be postoperative ileus (POI). There is reasonably good evidence that early return to feeding reduces postoperative ileus.(4) Aside from this principal, horses that do develop POI, current treatment includes continued use of anti-inflammatory drugs and lidocaine. Studies have shown that COX-2 inhibitors may be more beneficial than non-selective NSAIDs because they are capable of managing pain in preclinical trials without inhibiting intestinal repair.(9) Interestingly, concurrent use of lidocaine (1.3mg/kg loading dose, 0.05mg/ml CRI) also improves intestinal repair.(10) There has also been one clinical trial showing that lidocaine reduced the length of time and amount of reflux,(11) but more rigorous clinical trials are needed to discern the utility of lidocaine. It is possible that the effect is negligible, whereas the cost can be prohibitive because of the need to deliver the drug as a CRI. The last phase of postoperative management in the hospital is the adhesion phase, which begins to be clinically evident within 3-5-days of surgery based on recurrent episodes of colic and other known risk factors (small intestinal surgery, strangulating obstruction).(12) Aside from intra-operative treatments including carboxymethylcellulose, there is relatively little that has been shown to be effective in reducing adhesions. There are also other postoperative complications that occur less frequently, including laminitis, which can be devastating. The greatest advance in treatment of laminitis has been the use of ice to markedly reduce the temperature of the feet continuously in any horse at risk of laminitis,(13) and this may improve long term results.
What is the expectation for long-term outcome?
An understanding of what the owners expectation re can make a big difference in how to define long-term outcome. For example, if the expectation is solely to save the horse’s life, then considerations over incisional hernias or other long-term management problems such as laminitis can be more readily managed within the owner’s expectations. Owners can also be shown long term analyses based on the type of lesion their horse had to make sure expectations are realistic. For example, the prognosis is considerably lower for horses with small intestinal strangulation and simple obstruction.(14) Alternatively, if owners expect a return to athletic performance, management of long-term complications becomes that much more critical, and complications such as incisional hernia may require an additional surgery to correct. Other improvements that can potentially be made include reducing recurrent colic, for example by considering ablation of the nephrosplenic space in horses with repeat episodes of left dorsal displacement, or pexy of the colon in horses with repeat episodes of large colon volvulus. The latter tends to preclude athletic performance because of colic, but is particularly useful in broodmares that are at greatest risk of large colon volvulus. Resection of the colic is an alternative consideration to pexy, allowing return to athletic performance. Larger studies to improve our understanding of long-term outcome are needed, and beginning to be performed.
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[1] Hackett ES, Embertson RM, Hopper SA, Woodie JB, Ruggles AJ. Duration of disease influences survival to discharge of Thoroughbred mares with surgically treated large colon volvulus. Equine veterinary journal. 2015;47(6):650-4.
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