Final answer:
The priority action for a nurse when a client experiences ventricular fibrillation is to defibrillate, with chest compressions being the next best option if an AED is not immediately available.
Step-by-step explanation:
A nurse caring for a client experiencing ventricular fibrillation should prioritize defibrillation. However, if a defibrillator is not immediately available, initiate chest compressions is the correct priority action. This situation is described as a 'code blue' emergency in a hospital setting, and without prompt treatment, it could lead to brain death. In cases of ventricular fibrillation, defibrillation is the most effective method for attempting to reestablish a normal sinus rhythm by applying a controlled electrical shock to the heart. Automated external defibrillators (AEDs) make it possible for both medical professionals and laypersons to administer life-saving defibrillation in various public settings.