Aetiology

The aetiology is multi-factorial and is related to a disruption in the normal motility of the intestine. Predisposing factors include:

  • Electrolyte imbalances

  • Release of inflammatory agents

  • Deregulation of the sympathetic and parasympathetic input to the gastrointestinal tract

  • Exogenous compounds, such as analgesics and anaesthetics.

Predisposing factors are most likely to occur after gastrointestinal surgery, but may also occur with:

  • Non-abdominal surgery (thoracic, cardiac, or extremity)[23][24]​​

  • Other retroperitoneal pathology such as aortic or urinary disorders[6]

  • Acute or systemic illness (e.g., myocardial infarction, acute cholecystitis, pancreatitis, peritonitis, sepsis)

  • Pharmacological agents (e.g., opioids, anticholinergics)

  • Multi-organ trauma[24]​​

  • Cardiopulmonary bypass.[18][24]​​

Pathophysiology

Gastrointestinal motility is controlled by neurogenic, hormonal, and inflammatory factors.[25] During the postoperative period, catecholamine levels are higher than usual, which is believed to contribute to decreased gastrointestinal motility. This also occurs in other non-surgical conditions, including systemic illnesses, sepsis, and trauma. Gastrointestinal motility is inhibited by nitric oxide, vasoactive intestinal peptide, calcitonin gene-related peptide, and substance P.[6][26]​​ Studies in animals have shown that antagonists to these substances may improve postoperative ileus, although this has not been substantiated in humans.

In addition, corticotropin-releasing factor levels rise as part of the stress response, causing a delay in gastric emptying. The macrophages in the wall of the intestine are activated by bowel manipulation and secrete various substances (nitric oxide, prostaglandins, COX-2, interleukin-6, tissue necrosis factor alpha) that contribute to the decreased motility of the gastrointestinal tract.[26][27]​​

Classification

Classification according to type of ileus

Postoperative ileus

  • The normal slowing of bowel motility in response to the trauma of surgery. This usually follows gastrointestinal surgery but is also associated with non-abdominal surgery.

  • Motility typically returns first in the small bowel (<24 hours), then in the stomach (24-48 hours), and finally in the large bowel (>48 hours).[2] Resolution of ileus is signalled by the passage of stool or flatus and tolerance of an oral diet, though definitions of resolution of ileus are not consistent across published literature.[3][4][5]

  • In some patients, prolonged postoperative ileus develops, which is defined as two or more of the following occurring on or after day 4 post-surgery without prior resolution of postoperative ileus:[6][7]

    • Vomiting

    • Abdominal distension

    • Inability to tolerate oral feeding

    • Absence of flatus.

Ileus with systemic illness

  • Paralysis of bowel motility accompanying certain acute illnesses, such as myocardial infarction, acute pancreatitis, sepsis, and gastrointestinal disorders.

Narcotic ileus

  • Slowing of bowel motility associated with opioid use, thought to be caused by opioid action on mu receptors.[6][8]

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