Although there has been a substantial increase in our understanding of postoperative complications in recent years, the treatments
remain very much the same. For ileus, these treatments include decompression of the stomach, replacement of fluid and electrolyte
losses with parenteral fluids, and use of a variety of prokinetic agents. For adhesions, treatments include anti-inflammatory
medications and antibiotics, although some of the newer physical agents such as carboxymethylcellulose offer new modalities
for combating this problem. However, in order to make further advances in treatment of these problems, a close appraisal of
the clinical and basic science literature is warranted so that new therapies can be based on an understanding of the mechanisms
that result in ileus and adhesions.
Clinical aspects of postoperative ileus
Postoperative ileus in the horse is essentially a syndrome related to abnormal small intestinal motility because it is identified
on the basis of proximal gastrointestinal reflux. Thus, although there are horses with abnormal large intestinal motility
following colic surgery, the term postoperative ileus has not included these cases in most studies. This is because abnormal
small intestinal motility, with the attendant reflux of stomach contents, is readily recognized as an important cause of postoperative
mortality. Recent studies indicate that the prevalence of ileus amongst horses with signs of colic taken to surgery for abdominal
exploration ranges from 10% to over 40% depending upon the study population and the criteria for defining cases of ileus.
The criteria for defining ileus vary widely. For example, one study regarded any horse with >2L reflux to have postoperative
ileus, whereas another study defined cases of postoperative ileus as horses with >20L during a 24-hour period, or >8L during
any single refluxing event. However, it is likely that these studies are evaluating a similar population of horses, with differing
levels of severity, since horses had other important features of the syndrome of postoperative ileus, including an increase
in heart rate and signs of colic. Risk factors for postoperative ileus can be grouped into two important categories: those
related to the degree of circulatory shock, and those related to surgery. For example, elevated heart rate and packed cell
volume in the preoperative period place horses at risk of postoperative ileus, and small intestinal surgery, particularly
involving strangulating obstruction, place horses at risk of postoperative ileus. These groups of factors have been consistently
linked in two studies using multiple logistic regression analyses, suggesting that the degree of shock and the nature of the
intestinal lesion are intimately linked, and combine to place horses at risk of postoperative ileus.
Not all studies suggest such a high prevalence of postoperative ileus, which may relate to differences in disease management.
For instance, Freeman and coworkers were able to show that of horses taken to surgery for small intestinal disease, only 10%
developed postoperative ileus. One key management factor that may differ from other hospitals was early re-feeding, where
horses were offered water and small amounts of hay within 18-24-hours of the completion of surgery. Conversely, many surgeons
will hold horses off feed for at least 24-hours before contemplating a return to feed. The work by Freeman and coworkers suggests
that this is not optimal. Regardless of prevalence data, postoperative ileus appears to contribute significantly to postoperative
mortality. The percentage of horses that die in the postoperative period from ileus ranges from 9 to 43%. Considering that
these deaths are all short-term deaths (within the period of the initial hospitalization), postoperative ileus is one of the
major reasons for a substantial drop in survival noted in the early postoperative period. These deaths are typically elective
(euthanasia at the owners request or surgeon's recommendation), and usually relate to the inability to manage the degree of
shock associated with continued copious reflux, or the requirement for additional surgical procedures in order to evaluate
recurrent colic in the face of ileus. One study noted that in horses undergoing small intestinal surgery, the occurrence of
postoperative ileus was the single greatest risk factor for death (horses with ileus were 29-fold more likely to die than
horses without ileus).