Definition
Postoperative ileus is an iatrogenic situation in abdominal surgery. Indeed, the opening of the peritoneal cavity and manipulation of the digestive tract trigger a chain reaction. This reaction involves many complex neurological, inflammatory, hydro-electrolytic and pharmacological mechanisms, all of which lead to transient paralysis of the digestive tract and a halt in peristalsis. Not all segments are affected to equal extent. Small intestine motility is disrupted within 24 hours, gastric motility from 24 to 48 hours and colonic motility from 48 to 72 hours post-surgery(Benson et al., 1994). The time difference to recovery of motor function explains why the passage of the first stool and gas is most frequently used to define the return to normal function. The complexity of the definition lies in the fact that the return of the migrating motor complex is not synonymous with a return to normal function, i.e. perception of peristalsis at auscultation is not indicative of a return to normal transit. Nevertheless, a recent literature review of 215 articles identified a total of 73 criteria defining the return of normal transit(Chapman et al., 2019). Thus, in decreasing order of frequency, we find: passage of the first gas (140 studies out of 217, 64.5%), passage of the first stools (69 studies out of 217, 31.8%) followed by the first intestinal movements (65 studies out of 217, 30%)(Chapman et al., 2019). The commonly accepted outcome to assess the pharmacological effects of POI treatment is the resumption of solid food combined with the first defecation (van Bree et al., 2014).
Several studies have been carried out to propose a definition and standardise the semiological and clinical framework of postoperative ileus. Recent works include the American Society for Enhanced Recovery After Surgery (ERAS) study and the Perioperative Joint Consensus which considered a more functional definition of POI and a grading system for postoperative gastrointestinal transit disorders(Hedrick et al., 2018). A classification was proposed on a pathophysiological and functional basis using the following criteria: tolerance of oral ingestion, nausea, vomiting, physical signs of ileus (Intake, Feeling nauseated, Emesis, physical Examination and duration of symptoms “I-FEED”). A three-category classification system was therefore established:
- Normal (I-FEED score of 0-2)
Patients in this category tolerate a symptom-free diet, but may experience transient feeding difficulties with postoperative nausea and vomiting (PONV). PONV are considered non-pathological in the first 24-48 hours following surgery.
- Post operative gastro-intestinal intolerance POGI (I-FEED score of 3-5)
These patients usually do well initially, but begin to experience nausea 48 hours after surgery. They present with nausea, small volume non-bilious vomiting and bloating. The majority of patients tolerate drinking and do not require a nasogastric tube.
- Postoperative gastrointestinal Dysfunction (POGD) (I-FEED score ≥ 6)
POGD is the most severe form of impaired GI recovery and corresponds to what is considered ileus by most clinicians. These patients develop abdominal distension with tympany, anti-emetic resistant nausea and large volume bilious vomiting. This is associated with intolerance to oral ingestion. Specific treatment is required. Intravenous hydration and maintenance of fluid and electrolyte balance are necessary to maintain proper renal function. A nasogastric tube is also essential to prevent aspiration.
Secondary POI can also occur. This is defined by the same symptoms but is caused by a surgical complication such as anastomotic fistulae or another postoperative septic complication for which aetiological treatments based on the causal treatment of sepsis are administered (Chapman et al., 2018). Secondary ileus will not be dealt with here as it is usually managed surgically.
Pathophysiological studies have identified at least two phases in POI - an early phase involving neural pathways, known as the “neurogenic phase”, and a later phase, characterised by inflammatory features.
A third pharmacological phase occurring ”parallel” to the two previous phases is also apparent. This phase is essentially conditioned by the use of opioid. Opioids, often used as analgesics after different types of surgery, have a major impact on GI motility through the activation of μ-opioid receptors on myenteric fibres. This leads to inhibition of acetylcholine release from myenteric neurons and a reduction in GI transit (De Winter et al., 1997b; Holte and Kehlet, 2002). Interference with this mechanism by peripheral selective opioid antagonists will be discussed in detail later.