In a post-procedure assessment of a client with a duodenal ulcer, which symptom indicates a potential complication?

A rigid, boardlike abdomen after a procedure for a duodenal ulcer may indicate a serious complication such as perforation or peritonitis. This symptom suggests that there is irritation or inflammation in the abdominal cavity, possibly due to an underlying issue related to the ulcer.

In conditions like perforation, the contents of the gastrointestinal tract can leak into the abdominal cavity, leading to infection and severe abdominal pain. The rigidity of the abdomen results from the body's instinctive reaction to guard against further pain and injury, a phenomenon known as "guarding." Therefore, when a patient presents with this symptom, it is crucial to assess them further as it may require immediate medical intervention, such as surgery, to address the complication.

While bradycardia, nausea and vomiting, and numbness in the legs can be concerning in their own contexts, they do not specifically signal the same immediate and severe complication that a rigid, boardlike abdomen does, which makes the latter the most critical symptom to note in the post-procedure assessment.