I've just remembered this (I've been mega busy with work and exams).
Some general notes on CPR...
Place hands on centre of chest. Rate should he around 120 compressions per minute at a depth of 5-6 cm with the heel of your hand (one hand on top of the other). If you know how to give rescue breaths then do so but make sure to manually clear the mouth of debris or vomit first and remember to tilt the head back. If the person has a suspected spinal injury then NEVER tilt the head back. If the person was familiar with the jaw thrust maneuver then this could be done but best just stick to compressions. Handy to have someone to take over if possible as continuous CPR is very tiring..
A good idea would be to have a look on you tube to see a demonstration of correct cpr technique.
I know it seems unlikely that an OD would take place in a public area but if it does and there is an AED (automated external defibrillator) then get this out straight after calling 999 these can be used with little to no training as they're voice prompted and have diagrams and instructions on the box. They assess the cardiac rhythm and deliver the shock automatically so it's difficult to go wrong. Once a person's heart has stopped their chances of survival go down by 7-10% every minute until a shock is delivered.
If you have narcan to hand then administer is as soon as the person has overdosed although if the person has already gone into cardiac arrest then narcan will be useless.
In terms of prognosis then after the person has gone into respiratory arrest cardiac arrest soon follows and it then depends on the quality of cpr, the use of a defib and the type of cardiac rhythm the person has. An AED as mentioned above will only shock Ventricular Fibrillation but the type of defib carried by paramedics will shock VF and pulseless Ventricular Tachycardia (heart rate >160) as well.
It really all comes down to time.
If you catch the person as soon as possible after overdose then narcan should bring them out of it. Any later than that and cardiac arrest will result. The persons only chance then is good CPR and the prompt arrival of paramedics. If an AED is available and you can use it then do so (if the person is not breathing and has no carotid pulse then this implies cardiac arrest but the machine will determine if the person is shockable)..
I wish I could think of anymore to write but I can't.
My best suggestion is go on you tube and see a demonstration of correct CPR technique and maybe look at how an AED works...Most importantly call an ambulance straight away....DO NOT DELAY FOR ANYTHING...
stay safe folks
Also...Yes sprout that perspective would be useful I think. Please do contribute.