An anti-reflux valve developed to help esophageal cancer patients also has been shown to help those with bile duct obstruction, according to Kulwinder S. Dua, M.D., a research physician at the Medical College of Wisconsin in Milwaukee. The study, using the anti-reflux biliary stent in patients with cancer of the pancreas or bile duct, appears in the May issue of Gastrointestinal Endoscopy journal.
This bile duct stent with the "Dua Anti-Reflux Valve," named after its inventor, was cleared for use by FDA last year. The Dua stent, for short, has also been approved for use in Europe and Canada.
The bile duct carries bile from the liver to the intestines. When this duct is obstructed from cancers of the pancreas, gallbladder, or bile duct, bile begins to backup resulting in jaundice, itching, fever, chills, other organ malfunctions and death. About 30,000 new patients with pancreatic cancer and 4,000 new cases of bile duct cancer are diagnosed in the United States each year, most frequently in older people.
Surgery to remove the tumors is generally the best treatment, but often the disease has progressed too far to consider surgery. Consequently, a stent, a tiny, hollow tube, is inserted using a minimally invasive procedure to help improve the passage of bile. However, these stents frequently clog requiring repeat procedures to replace the clogged stents. The exact mechanism that leads to stent clogging is not known. There is a possibility that clogging occurs from contents from the intestines backflowing (refluxing) into the stent.
The "Dua Anti-Reflux Valve" was initially developed to reduce reflux of stomach contents in patients with cancers of the esophagus. Resembling a windsock, it functions as a pressure-sensitive valve that closes when stomach pressure increases thereby preventing reflux. However, when the pressure builds beyond a certain point, the valve inverts allowing for belching or vomiting. By drinking one gulp of water, it reverts to its anti-reflux position.
The U.S. Food and Drug Administration cleared the "Dua Esophageal Stent" for use by patients with esophageal cancer in 2002. Using a similar windsock design, Dr. Dua modified the valve and attached it to the bile duct stent that closes whenever the pressure in the intestines increases so as to prevent backflow into the bile ducts.
Laboratory studies to evaluate the flow dynamics of this modified stent showed that its valve was effective in reducing backflow while maintaining its primary function, namely forward flow.
Dr. D.N. Reddy from the Asian Institute of Gastroenterology in Hyderabad, India, conducted a study on 60 consecutive patients in whom the bile duct was obstructed from cancer of the pancreas or the bile duct. He placed a standard biliary stent in 30 patients and the Dua stent in the remaining 30 patients. Addition of the anti-reflux valve on the Dua stent did not compromise the main function of the stent, i.e. bile drainage as both stents were equally effective in improving liver tests, and complication rates were similar.
The study showed that the stent with the Dua anti-reflux valve remained functional for a median of 145 days compared to 90 days in those with a standard stent. This resulted in fewer repeat endoscopies for stent changes in patients with the Dua stent. There were six patients in the anti-reflux stent group in whom the stent remained patent for six months and longer compared to only one such patient in the standard stent group.
"In patients with advanced cancers causing bile duct obstruction in whom life expectancy is limited, this difference may translate into fewer procedures to maintain bile duct patency. That means a better quality of life for these cancer patients," says Dr. Dua.
"Our next step is to do electron microscopic analysis of clogged standard and anti-reflux stents to evaluate the role of reflux of intestinal contents in stent clogging," Dua says. "We also hope to look at other uses for this type of stent."
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