Shout for help. Try to wake person by shouting “Hello! Are you OK?” and gently shaking their shoulders
Check for pulse (may be weak). Feel inside wrist and/or carotid artery under jaw.
Breathing? Place person on their back. Watch chest for 5 seconds, place ear close to mouth and listen or feel for breath on the ear.
Ask bystander to phone 911. If alone, use your cell phone and put it on “Speaker” so you can lay it down while you respond to questions. Do not hang up unless permission given.
Not breathing? Airway clear? Tilt person’s head back, raising chin. Be very gentle in case of spinal damage. Look in airway for foreign objects and remove them if possible.
CPR (cardiopulmonary resuscitation): place palm of one hand in centre of chest, at base of breast bone. Place other hand on top, interlacing fingers. Straighten arms, place your weight vertically above pressure point and push hard and fast. Push down 5 or 6 cm (2”) and release, twice per second, allowing the chest to expand completely at the end of each compression.
If an AED is handy, ask someone to fetch it, and follow instructions given by the apparatus. Do not stop compressions until AED or EMS personnel request it.
Keep arms straight to reduce fatigue.
If person begins breathing, place in “response position”, by rolling onto their side, with lower arm under their head, upper leg bent 90 degrees at knee. This prevents vomit from clogging airway.
Background:
https://www.healthing.ca/injury/unconsciousness-first-aid,
https://www.ncbi.nlm.nih.gov/books/NBK469741/
Summary: