Description of the condition

The modern meaning of the ileus condition reflects the absent or reduced peristalsis that can be attributed to a normal, prolonged, or pathological response of the gastrointestinal tract. This failure of peristalsis results in the accumulation of gastrointestinal secretions leading to abdominal distention and nausea, possibly vomiting [1].

By this definition, postoperative ileus is a transient cessation of coordinated bowel motility after surgical intervention, which prevents effective transit of intestinal contents or tolerance of oral intake resulting in the presence of nausea, vomiting, and the failure to pass flatus or stool [1]. Furthermore, it may become a source of pain and discomfort for the patient and leading to the consequent onset of impaired nutritional requirements and protein deficiency and, therefore to increased risk of infection, delays in hospital discharge increasing costs [2–4].

In the literature, some authors as Bragg et al. [1] and Holte & Kehlet [5], described how the return of a normal gastrointestinal function after surgery follows, in most cases, three stages: 1) the small bowel recovers between 0 and 24 hours, 2) the stomach between 24 and 48 hours and 3) the colon between 48 and 72 hours. However, other authors like Delaney et al. [6] state that gastric and small bowel activities should return to normal function just a few hours after surgery. As this background, it is still debated how to distinguish between a physiological and a prolonged status of ileus. Moreover, postoperative ileus (POI) is a common response to abdominal surgery, with an estimated incidence between 17% and 80% [7]. The high variability of incidence reported in the literature reflects the absence of an established and shared definition of what can be accepted as a “normal” duration of the intestinal paralysis [1, 3]. Nevertheless, Lee et al. [8] highlighted that postoperative ileus could be considered resolved if the following requirements are concomitantly present: food tolerance, absence of abdominal distension, the passage of flatus, or stools.

Because of the lack of consensus regarding the POI definition, some uncertainties remainy regarding its assessment and therefore regarding which outcomes may be the most appropriate to evaluate. Many different effects have been proposed in the literature as an expression of POI resolution, such as the reappearance of bowel sounds and passage of flatus or bowel movement, tolerance to fluid and food consumption, and reinsertion of the nasogastric tube together with the presence of bowel sound. However, these seem to be poor markers of Ileus recovery [9].

Currently, the most effective approaches for postoperative ileus tend to be focused on prevention rather than treatment. Some interventions, as the adoption of minimally invasive surgery [10], perioperative fluid management strategies based on the “Goal-Directed Therapy” [11], and the use of local epidural anaesthetics in lieu of opioid-based analgesic regimens [12], have been thoroughly studied and have been considered effective for ileus prevention.

One of the five key component of the ERAS (Enhanced Recovery After Surgery protocols) program [13] is enforced early feeding. In current practice, early feeding is reached using different kind of interventions such as chewing gum, [4] coffee consumption [14], sips of water clear fluid, tube feeding and so on, sometimes a combination of these interventions can be proposed [9, 15]. Chapman and colleagues [4] reported that early postoperative feeding compared with traditional (or late) timing was safe and reduced length of hospital stay; nevertheless, they reported small effects in hospital discharge with an uncertain clinical significance, shoving minimal effects on a several measurement of gastrointestinal function. Although early oral feeding is considered by the international literature a common and safe intervention for postoperative ileus prevention, the current evidence regarding early versus delayed postoperative feeding does not highlight any significant change regarding the incidence of wound infections, intra-abdominal abscesses, or pneumonia [16]. Therefore, the effectiveness of early postoperative feeding to reduce ileus duration remains debated.

Description of the intervention

Over the last few years, early postoperative feeding (within 24 hours from surgery) was among the many preventive multimodal interventions introduced in the Enhanced Recovery After Surgery protocols (ERAS). The ERAS has been proven effective in accelerating the post-surgical recovery and reducing hospital length of stay, although the relationship between early feeding and ileus has not yet been directly evaluated. To date, it has been considered safe to resume feeding early in the postoperative period without the risk of negative impacts on the anastomosis dehiscence [17].

How the intervention might work

Early oral nutrition allows the gastrointestinal system to regain its physiological status and functions more rapidly than parenteral nutrition and specifically stimulates motility, which will allow a faster first passage of flatus and stools [18]. In addition, on the one hand, early oral nutrition would prevent significant metabolic changes that occur within 24 hours of starvation, such as increased insulin resistance [19]; on the other, it would readily provide the fundamental constituents for surgical wound healing.

Why it is important to perform this review

The postoperative time and day to be considered safe to resume oral intake and the concept of “early feeding” is still discussed and varies widely between surgical contexts. Moreover, there is no shared definition regarding the most appropriate outcomes that need to be used to evaluate postoperative ileus and the most appropriate time and nutrients to administer to stimulate peristalsis.

The intervention “feeding” itself remains vague due to the lack of consensus regarding what is considered feeding (liquids versus solid food, for example) and what is the best approach in terms of types of nutritional components routinely prescribed to the patients to improve intestinal motility, which may vary widely across surgical settings and cultures and therefore being context specific.

Most of the previously published systematic reviews considered only colorectal [9, 20, 21] or lower gastrointestinal surgery [16], or assessed other primary outcomes rather than POI, such as length of stay (LoS) and postoperative complications [23].

The strategies currently used to improve postoperative intestinal motility concerning oral feeding include the administration of sips of water, clear fluids, coffee, restrictions to or combination of certain food types [4].

Study registration

This systematic review has been registered prospectively in the International Prospective Register of Systematic Reviews (PROSPERO) the registration number is CRD42022298777.

The protocol aligns with the PRISMA-P guidelines [22], and the checklist is available in S1 Appendix.

Criteria for including studies in this review

Search methods for identification of studies

Pubmed, Embase, Cinahl, Cochrane Central Register of Controlled Trials (CENTRAL), and the ClincalTrials.gov register will be searched to identify the RCTs of interest. Additionally, the SIGLE System for Information on Grey Literature (SIGLE) will be consulted to identify further studies or papers not published. The bibliographic references will be revised, and, if necessary, the corresponding authors will be contacted to clarify doubts and consider unpublished data.

Data collection and analysis