What is required immediately for adults, children, and infants who exhibit no signs of effective breathing and no pulse?

The correct answer is CPR, which stands for cardiopulmonary resuscitation. This technique is necessary for adults, children, and infants who show no signs of effective breathing and have no pulse because CPR serves to manually preserve brain function until further measures are taken to restore spontaneous blood circulation and breathing in an unconscious victim.

CPR combines chest compressions and rescue breaths, which helps circulate blood to the brain and other vital organs. When a person has no pulse, it indicates that their heart is not pumping blood effectively; thus, immediate action is critical. Starting CPR promptly can significantly increase the chances of survival and reduce the risk of long-term damage.

While rescue breathing might provide oxygen support, it is not sufficient alone without chest compressions. Advanced life support involves more complex interventions and is typically provided by emergency medical professionals, which is not immediately available in an urgent scenario. Emergency oxygen can assist in providing oxygen to the respiratory system but can only be administered effectively after circulation has been established. Therefore, CPR is the immediate lifesaving measure required in this critical situation.