The ABC of first aid is a mnemonic designed to help people remember how to respond to an emergency situation in which someone is injured. Numerous other mnemonics and variants on the ABC of first aid exist, but it is probably the most useful one for lay people to remember. The letters stand for Airway, Breathing, and Circulation, also referred to as the vital signs. If all of the vital signs are monitored and addressed, a patient has a much better chance of surviving until trained help arrives.

Some emergency services prefer the variant DRABC, to remind people to check for danger in a situation before assisting someone. The DR stands for Danger and Response, and means that people should first examine the environment and then the patient, to ensure that there is not a source of potential physical danger. For example, an unconscious patient next to a live wire should be treated, but not until the live wire has been turned off or the patient can be moved out of the way, to ensure that the responder is not injured as well.

When using the ABC of first aid, the first thing to do is check the patient's airway. If someone's throat is blocked, he or she will be unable to breathe. If the patient is conscious, you can ask the patient to talk to you. If the patient is unconscious, lift his or her chin and tilt the head back. Do this carefully, as you may aggravate spinal and neck injuries by manipulating the head. Sweep the back of the mouth with a finger to check for obstructions if you suspect that someone may have a compromised airway.

Next, check for breathing. Place your face close to the patient's mouth to listen and feel for breathing, or use an object like a mirror. If the patient is breathing, the breath will condense on the mirror. If the patient is not breathing, according to the ABC of first aid, you need to correct the problem before moving on to the next step. Administer rescue breathing and CPR until the patient is breathing again.

Finally, circulation should be checked by monitoring the patient's pulse at the wrist or throat. In addition, check the patient's color. If he or she is pallid or has splotchy areas of color, it suggests that the circulation may be compromised. Try to keep the patient warm. By following the ABC of first aid, you can ensure that the patient's basic needs have been met, allowing you to move on to more general treatment.

If all of the steps of the ABC of first aid are satisfied, responders can move on to a general assessment of the patient, looking at injuries and their severity. Responders constantly check the vital signs while they work on the patient, to ensure that the patient is still stable. The ABC of first aid may diverge here into a plethora of options, depending on the patient's condition. If you are first on the scene and have no medical training, however, just try to focus on the ABC of first aid, and apply pressure to obvious sites of bleeding.