Final answer:
The staff nurse should pause the check and sign out of the medication dispensing system until the charge nurse can return to continue the controlled substance verification process properly.
Step-by-step explanation:
When a staff nurse is assisting a charge nurse with the checking of controlled substances and the charge nurse must leave abruptly, the most appropriate action for the staff nurse to take is to pause the check until the charge nurse returns. This action is necessary because controlled substance checks are a critical process, usually requiring dual verification to ensure accuracy and prevent misuse or diversion of medications. If the staff nurse continues alone or leaves to find another nurse, it may disrupt the controlled substance count or lead to inaccuracies. It is essential to sign out of the medication dispensing system to maintain the integrity and security of the medication management system until the process can be properly resumed.