Final answer:
The immediate and appropriate action for an athletic trainer when an athlete is unconscious with signs of cardiac arrest is to initiate CPR and use an AED if available.
Step-by-step explanation:
If an athlete is unconscious with a weak pulse, tachycardia, and apnea after displaying difficulty breathing during a pre-game meal, the most appropriate immediate action for the athletic trainer to take is to initiate CPR. This is because the athlete is showing signs of cardiac arrest, a condition where the heart is not pumping blood effectively, which is a medical emergency that requires immediate intervention. After CPR is initiated, if an Automated External Defibrillator (AED) is available, it should be applied as soon as possible.
An AED automatically diagnoses the heart's rhythm and applies a shock with appropriate energy and waveform if necessary. The device is designed to be used by anyone and provides verbal instructions to help responders through the process. It's important to remember that CPR often precedes the use of an AED and both are critical steps in resuscitation efforts.