Air-fluid levels are seen on upright films. Most small bowel gas comes from swallowed air, and the purpose of an N-G tube is to prevent the further accumulation of air in the obstructed bowel. It also prevents vomiting and aspiration. The tube does nothing to relieve the distention already present. Free air is best seen under the diaphragm on upright chest X-ray. The patient must be upright for 10 minutes before the film is taken.
The smaller the hernia, the more likely is incarceration and strangulation (see strangulated femoral hernia.) As the lymphatics, veins and arteries become successively compromised by the build-up of edema fluid, the wall necroses, thins and finally perforates. The decompressed knuckle of bowel can then slip back into the abdominal cavity and cause generalized peritonitis.
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