The investigators in this study aim to examine a plausible mechanism by which gastrointestinal dysfunction, gastric dysmotility and loss of epithelial barrier integrity, occur in critical illness. Specifically, the investigators will examine whether an increase in PAR2 agonist levels, zonulin and serine proteases, are associated with gastric dysmotility and loss of epithelial barrier integrity in critical surgical illness in children. The investigators will examine GI function, gastric motility and epithelial barrier integrity, and PAR2 agonist levels, zonulin and serine protease, in participants before surgery and after surgery. Specifically, children undergoing posterior spinal fusion, a known significant inflammatory trigger, and with planned admissions to the intensive care unit will be enrolled. Gastrointestinal function and PAR2 agonist levels will be tested non-invasively in blood and stool.
