What indicates that an adult patient is experiencing cardiac arrest?

The scenario that indicates an adult patient is experiencing cardiac arrest is when the patient has no pulse and is not breathing. Cardiac arrest occurs when the heart stops pumping effectively, leading to a lack of blood flow to the body's organs, including the brain.

When a patient is unresponsive and has no detectable pulse, it signals that the heart is not functioning, which confirms cardiac arrest. In this state, immediate intervention is critical, as the likelihood of survival decreases rapidly without prompt cardiopulmonary resuscitation (CPR) and potential defibrillation.

In contrast, the other scenarios described reflect different conditions. A patient who is breathing but unresponsive may be in a state of altered consciousness or respiratory depression but does not indicate cardiac arrest. A patient who is alert but in pain displays responsiveness and some level of circulation. Lastly, a weak pulse accompanied by gasping indicates severe distress but not a complete cardiac arrest, as some blood circulation is still present. Thus, the presence of no pulse and no respiration is the definitive indicator of cardiac arrest.