Post operative ileus (POI): Another perspective

Merritt and Blikslager (2008) present an excellent challenge to re-examine attitudes towards definition and diagnosis of post operative ileus (POI) in horses. An intriguing aspect of this complex disease is that diagnosis is made largely on the basis of reflux through a nasogastric tube. This is tantamount to diagnosing navicular disease on the observation of a forelimb lameness or pneumonia because of an elevated respiratory rate. Of course, other signs offered to support the diagnosis of POI are reduced faecal output and absence of intestinal sounds. However, these 2 findings can be attributed in part to reduced perioperative food intake (Tasker 1967; Freeman et al. 1989; Naylor et al. 2006) and associated decrease in gastrointestinal tract motility (Ross et al. 1990). Therefore, post operative reflux is a clinical finding and should be regarded as such in each case until a cause is established. Often overlooked in discussions of equine POI is the contribution from mechanical factors. In 3 studies, high heart rate, high PCV, small intestinal involvement, increased duration of anaesthesia and increased duration of surgery emerged as significant risk factors (Blikslager et al. 1994; Roussel et al. 2001; Cohen et al. 2004). These are clearcut markers of the severity of the primary disease and of cases with the most complex surgeries. In addition, these horses are at greatest risk of developing mechanical obstruction from a surgical complication or error, critical factors that the studies did not address. The current explanation of pathogenesis for POI is that selective manipulation of the small intestine causes sufficient inflammation in the intestinal muscle layers and myenteric neural plexus to disrupt motility (Schwarz et al. 2004; Little et al. 2005). This theory is supported by the coincidence of substantial serosal inflammation with the onset of post operative reflux at approximately 18 h after surgery (Little et al. 2005). This interval could, however, just as readily represent the period required for sufficient fluid build-up, proximal to an incomplete mechanical obstruction, to produce reflux. Horses that undergo a successful repeat celiotomy may well experience the same duration of surgery and the same amount of intestinal manipulation as at the first surgery, but often recover from the second procedure without any evidence of POI (Freeman et al. 2000; Freeman and Schaeffer 2005a,b). If the proponents of the POI inflammation theory are correct, these horses should be at greater risk of developing POI; this does not appear to be the case. According to a series of studies from one hospital, the equine intestinal tract appears to be more sensitive to minor mechanical obstructions, imposed by different types and methods for anastomosis, than to POI (Freeman et al. 2000; Freeman and Schaeffer 2005a,b). No horse from these studies developed reflux after jejunojejunostomy (n = 32), whereas 26% (n = 5/19) refluxed following jejunocecostomy, possibly related to unique mechanical features of this anastomosis (Freeman 2005). It is noteworthy that, in the group of horses without reflux, a large proportion of those with a history of cribbing did so in the early post operative period (Archer et al. 2004), a manoeuvre that was well tolerated despite its potential to exacerbate gastric distention. Incidentally, these studies had the strictest definition of POI, specifically, any gastric reflux in horses that did not have a confirmed mechanical obstruction or proximal enteritis. More importantly, post operative treatments typically directed at preventing or treating POI were not used, including the médicament du jour (lidocaine). Also, all surgeries involved vigorous and complete (but careful) manual decompression of distended loops of small intestine, a likely cause of POI in horses based on the inflammation theory. Two important points should be considered: 1) many mechanical obstructions and surgical complications (e.g. small anastomotic lumen, intestinal rotation at or close to the anastomosis, mesenteric shortening or rotation, secondary intestinal displacements) can be missed by pathologists at necropsy; and 2) horses might adapt to or resolve some mechanical obstructions over time (e.g. anastomotic impaction, stomal stenosis, minor mesenteric shortening, adhesions, intestinal kinking at or close to the stoma). All these horses are then recorded as cases of POI, although many might benefit from a repeat surgery, with lower total cost, reduced nursing care, reduced drain on hospital resources, shorter hospitalisation time and, arguably, better prognosis. More importantly, a heightened awareness of the sensitivity of the horse’s small intestine to mechanical obstructions should redirect our efforts towards preventing these problems rather than relying solely on medical treatments for POI. D. E. FREEMAN University of Florida, College of Veterinary Medicine, Gainesville, Florida, USA.