Which abbreviation is used to indicate that a procedure or action should happen immediately?

The abbreviation that signifies a procedure or action should happen immediately is "STAT." This term originates from the Latin word "statim," meaning "immediately." In healthcare settings, using "STAT" alerts medical staff that urgent attention is required for a patient's condition or treatment, ensuring prompt delivery of care.

The other terms have different meanings: "After" does not convey urgency; "WNL" stands for "within normal limits," indicating that a patient's measurements or conditions fall within expected ranges; and "O2" refers to oxygen, commonly used to describe oxygen therapy or supplemental oxygen needs, not urgency in action. Thus, "STAT" clearly stands out as the correct choice for urgent action.