What action should be taken first if a nurse suspects a reaction during a blood transfusion?

When a nurse suspects a reaction during a blood transfusion, the most critical action to take first is to stop the transfusion immediately. This step is vital because ongoing transfusion could exacerbate the patient's reaction and potentially lead to severe complications such as hemolytic reactions, allergic reactions, or circulatory overload. Stopping the transfusion halts the exposure to the transfused blood that might be causing the adverse reaction, thereby protecting the patient's health.

After stopping the transfusion, the nurse would typically take several subsequent steps, such as notifying the physician, monitoring the patient closely for changes, and documenting the reaction in the medical records. However, the priority must remain on halting the transfusion to ensure the patient's safety and minimize any harm that could arise from continuing the procedure.