A patient presents to the ED with angioedema and visible tongue swelling but oxygen saturation remains stable. What is the nurse's priority action?

Angioedema involving the tongue is a true airway emergency because swelling can progress rapidly and occlude the upper airway with little warning, even when oxygen saturation appears normal at initial presentation. The nurse's priority action is to prepare airway equipment — including bag-valve mask, suction, and supplies for intubation or emergency surgical airway — because the window for securing the airway can close within minutes as edema worsens. Acting before saturation falls is consistent with the principle of anticipating deterioration rather than waiting for it. Providing reassurance is not appropriate; it minimizes a potentially life-threatening situation and delays action. Applying oxygen may be helpful but does not address the underlying mechanical obstruction that is developing. Administering an antihistamine is a secondary pharmacologic measure; while epinephrine and corticosteroids are part of anaphylaxis management, ensuring that equipment is ready to manage a compromised airway takes precedence in the sequence of nursing actions. Vigilant preparation for intubation or cricothyrotomy is the most critical immediate step, and this readiness is what differentiates a safe response from a reactive one that may come too late.