Which of the following actions should a dental assistant take at the completion of a dental procedure involving nitrous-oxide oxygen?

At the completion of a dental procedure involving nitrous oxide-oxygen, turning off the nitrous oxide is the correct action to take. This step is critical because nitrous oxide is a sedative agent used to help patients feel relaxed during dental procedures. Once the procedure concludes, it is essential to discontinue nitrous oxide to prevent any residual sedation and to ensure that the patient can safely return to their normal state.

In addition to turning off the nitrous oxide, it's standard practice to continue providing oxygen for a few minutes after discontinuation to help flush the nitrous oxide from the patient's system. This further aids in ensuring the patient's safety and comfort.

Options that involve increasing the oxygen dosage are premature since the procedure is completed. Administering more nitrous oxide is inappropriate once the procedure is over; it would only prolong sedation unnecessarily. While monitoring the patient is important throughout the procedure, the specific action needed after the procedure involves turning off the nitrous oxide. Thus, focusing on the immediate action of shutting off the nitrous oxide is fundamental to patient care post-procedure.