Final answer:
The nurse's first action should be to call a code and initiate CPR when a heart monitor indicates cardiac arrest, as it is a critical life-saving measure that maintains blood circulation until the heart can regain its rhythm.
Step-by-step explanation:
When a nurse working on the cardiac unit hears an alarm and finds that one of the heart monitor screens at the nurse's station is displaying a straight line, indicating a client is in cardiac arrest, the first action the nurse should take is to call a code and initiate CPR (cardiopulmonary resuscitation). In a cardiac emergency situation, immediate intervention is crucial, particularly CPR, which can maintain the flow of blood until the heart resumes beating. After applying CPR, the nurse might use an automated external defibrillator (AED) if available, as it can correct abnormal heart rhythms like ventricular fibrillation by delivering a shock to the heart.
Option 1, calling a code and initiating CPR, is the immediate and life-saving response. Notifying the client's family (Option 2), documenting the event (Option 3), and administering epinephrine (Option 4) should only be considered after the initial emergency response has been implemented. CPR is the first and most vital step in the chain of survival in cases of cardiac arrest. Proper technique and immediate action can make the difference between life and death.