(Acute Colonic Pseudo-obstruction)
Ogilvie syndrome, which is also known as acute colonic pseudo-obstruction, is a term used to describe a pathological dilation of the colon (ie: "large" intestine) in the absence of a mechanical lesion responsible for the dilation. This differs from colon obstruction caused by tumors, volvulus, strictures, or infection (ie: "mechanical" causes).
The underlying mechanism behind Ogilvie syndrome is not fully understood. The current working hypothesis is that the autonomic nervous system, which is partially responsible for gut motility, stops working properly.
Therefore, in order to understand Ogilvie syndrome, we have to understand a little about the autonomic nervous system. This branch of the nervous system is broken up into two parts: sympathetic and parasympathetic. The sympathetic nervous system is responsible for the "fight or flight" response and the parasympathetic system is responsible for the "rest and digest" response. When it comes to the colon, the parasympathetic system increases gut motility and the sympathetic system decreases motility.
Ok, so what is happening in colonic pseudo-obstruction? It is believed that there is an over-abundance of sympathetic input to the colon. This causes a failure of the gut to contract (aka: peristalsis) and therefore poop is not pushed along properly.
If the colon stops contracting then it starts to expand as mucous and stool fills it up. For unknown reasons, the most common part of the colon that is involved in Ogilvie syndrome is the cecum (first portion of the large colon) and the ascending colon.
Acute colonic pseudo-obstruction causes belly pain, nausea, and vomiting. In addition, since the colon is not contracting, many patients have obstipation (ie: a fancy term for intractable constipation).
If medical attention is not sought soon, the colon may perforate, which can cause peritonitis (infection of the abdominal cavity). Fever, chills, and frank septic shock may occur in the setting of colonic perforation and peritonitis.
Diagnosis is made when there is evidence of an enlarged colon with no mechanical obstruction. In essence, diagnosing Ogilvie syndrome is more about ruling out other causes of colon obstruction.
CT scans, abdominal xrays, barium swallow studies, and colonoscopies are commonly used as adjunctive means for diagnosing pseudo-obstruction.
Treatment of Ogilvie syndrome is typically conservative. This means making the patient NPO (ie: nothing by mouth) and placing a nasogastric tube (NGT) to suction. The NGT helps "decompress" the colon from above until the pseudo-obstruction resolves.
If conservative measures fail then a medication known as neostigmine can be given. Neostigmine is a parasympathetic "mimic". It blocks the breakdown of acetylcholine by inhibiting an enzyme known as acetylcholine esterase. Acetylcholine is the main neurotransmitter of the parasympathetic nervous system. Therefore, if there is more acetylcholine around, then more gut motility occurs (hence why neostigmine has become a very effective treatment for Ogilvie's syndrome, see pathology above).
Another medication known as methylnaltrexone may also be useful in cases of acute colonic pseudo-obstruction caused by opioids.
In cases that are refractory to conservative and medical therapies the use of colonoscopic decompression is extremely effective. Patient's who have evidence of colonic perforation require prompt surgical exploration. Surgery is typically used as a last resort, but is always necessary if perforation has occurred.
Ogilvie syndrome, or acute colonic pseudo-obstruction, is a pathologic dilation of the colon that occurs in the absence of a mechanical cause. It is believed to be the result of autonomic nervous system dysfunction. Diagnosis is made with xrays and CT scans of the abdomen. Treatment is with nasogastric decompression, neostigmine, methylnaltrexone, colonoscopic decompression, or surgery in advanced cases.
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