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Unfortunately some people don't get total relief with the reflux surgeries. Not just nissens though. I don't know any specific percentages or anything, I just know 2 of my surgeons have said this is a possibility. They usually don't have to be on high doses though.
I recently did have to go back on them temporarily because my nissen was torn apart by an esophagus stent to help my torn esophagus heal. We didn't know it had ruined the wrap until a couple months after the stent was removed.
Nissen 6/06 and 5/09
#3 on 8/24/11