Ogilvie syndrome

Ogilvie syndrome is the acute dilatation of the colon in the absence of any mechanical obstruction in severely ill patients. Ogilvie syndrome is the acute dilatation of the colon in the absence of any mechanical obstruction in severely ill patients. Acute colonic pseudo-obstruction is characterized by massive dilatation of the cecum (diameter > 10 cm) and right colon on abdominal X-ray. It is a type of megacolon, sometimes referred to as 'acute megacolon', to distinguish it from toxic megacolon. The condition carries the name of the British surgeon Sir William Heneage Ogilvie  (1887–1971), who first reported it in 1948. Usually the patient has abdominal distention, pain and altered bowel movements. There may also be nausea and vomiting. Ogilvie syndrome may occur after surgery, especially following coronary artery bypass surgery and total joint replacement. Drugs that disturb colonic motility (e.g., anticholinergics or opioid analgesics) contribute to the development of this condition. The exact mechanism is not known. The probable explanation is imbalance in the regulation of colonic motor activity by the autonomic nervous system. It has been postulated that reactivation of varicella zoster virus (which causes chickenpox and shingles) in the enteric ganglia may be a cause of Ogilvie syndrome. Acute megacolon develops because of abnormal intestinal motility. Normal colonic motility requires integration of myogenic, neural, and hormonal influences. The enteric nervous system is independent but is connected to the central nervous system by sympathetic and parasympathetic nerves. The targets of the enteric neurons are muscle cells, secretory cells, endocrine cells, microvasculature, and inflammatory cells. The neurons in the enteric plexuses are stimulated by a food bolus, which both distends the gut and stimulates the mucosal surface, leading to the release of factors that stimulate interneurons. The stimulated interneurons transmit excitatory signals proximally, which cause contraction and inhibitory signals distally, and these in turn cause relaxation. These signals are transmitted by the neurotransmitters acetylcholine and serotonin, among others. Acute megacolon can also lead to ischemic necrosis in massively dilated intestinal segments. This is explained by Pascal's law and Laplaces's law. Pascal's principle states that a change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid; the pressure across all parts of the lumen is equal. Laplace's law states that: T = P r 2 t {displaystyle T={frac {Pr}{2t}}}