Last week my wife had an operation to put a fistula in her left arm, just above the elbow. The surgeon checked it while she was in recovery and claimed it was successful. However, now, a week later, we cannot feel the "thrill" or hear, with the aid of a stethoscope, the whooshing sound we were told to check for. Neither could the nurse who removed the dressing yesterday, and she suggested a further scan to check its function. It may be due to swelling following the trauma of the operation but, should we be worried that the fistula is not working and what happens next?