Pathophysiology. According to some hypotheses, postoperative ileus is mediated via activation of inhibitory spinal reflex arcs

According to some hypotheses, postoperative ileus is mediated via activation of inhibitory spinal reflex arcs. Anatomically, 3 distinct reflexes are involved: ultrashort reflexes confined to the bowel wall, short reflexes involving prevertebral ganglia and long reflexes involving the spinal cord. The long reflexes are the most significant. Spinal anaesthesia, abdominal sympathectomy, and nerve-cutting techniques have been demonstrated to either prevent or attenuate the development of ileus.

The surgical stress response leads to systemic generation of endocrine and inflammatory mediators that also promote the development of ileus. Rat models have shown that laparotomy, eventration, and bowel compression lead to increased numbers of macrophages, monocytes, dendritic cells, T cells, natural killer cells, and mast cells, as demonstrated by immunohistochemistry. Calcitonin gene-related peptide, nitric oxide, vasoactive intestinal peptide, and substance P function as inhibitory neurotransmitters in the bowel nervous system.

Nitric oxide and vasoactive intestinal peptide inhibitors and substance P receptor antagonists have been demonstrated to improve gastrointestinal function.