The appropriate nursing action in this scenario is:
D. Notify the healthcare provider
Constipation occurring three days after a barium enema may be a sign of a complication or blockage related to the procedure. It's essential to notify the healthcare provider so that they can assess the patient's condition, determine the cause of the constipation, and provide appropriate guidance or treatment. Option C (performing a digital rectal examination) may not be indicated without the guidance of a healthcare provider, and administering a laxative (option A) without proper assessment and provider approval can be contraindicated in some cases. Therefore, notifying the healthcare provider is the safest and most appropriate action.