Emergency Medicine/Cardiopulmonary Arrest
For those already familiar with CPR, a summary of recent changes is at the European Resuscitation Council website. 
This summary summarizes changes under the categories : basic adult resusc, automated defibrillators, advanced adult , advanced paediatric ;
advanced adult is subdivided to order of CPR/defibrillation is a) defib first in professional witnessed arrest, b) defibrillation technique is one shock and CPR for 2 minutes before other shocks , c) doubtful fine VF is not worth shocking delay of CPR, d) adrenaline 1mg after 2nd shock or non VF/VT / rate is 3-5 minutely, e) vf/vt - amiodarone (load 300mg +/- 150mg, 900mg /24h) XOR lignocaine (max 3mg/kg/hr), f) PE/thrombolysis/prolonged CPR 60-90 minutes , g) hypothermia to 32deg for 12-24 hours definitely for out of hospital VF/VT, and maybe for all others ( in hospital all, out of hospital non VF/VT).
The principles might be: minimize circulation downtime ( a, b, c), provide drugs better or earlier (d e f), more tenacity in rescue ( f and g) .
ABC - airway , breathing , compression. This in general describes conceptual categories, but is also the sequence of management in CPR: airways first, breathing next, compression of the heart.
The exception is when immediate defibrillation is available, AND equipment to diagnose ventricular tachyarrythmia or ventricular fibrillation is available. Then the sequence is : observed unexpected collapse + known history suggests ventricular fibrillation: e.g. was complaining of chest discomfort -> attach equipment -> diagnose VF ( automatic or manual) -> attach defibrillation pads -> charge equipment to 200J (or wait automatic) -> warn bystanders -> defibrillate. If manual, defibrillate x 3 , before resuming normal CPR sequence if still in ventricular fibrillation.
This is taken from an observed successful resuscitation of a witnessed arrest , as applied by an experienced provincial emergency specialist nurse.
It has some contrast to the recommended DRABCD sequence as per Guideline 7, February 2006, of the Australian Resuscitation Council  , but is similar to the European Guidelines Summary of Changes 2005 .
The pros and cons are : the first scenario meets the minimum time to defibrillation for successful defibrillation criteria ; the first scenario maximizes the success rate of the cardiac arrest resuscitation, as VF/VT arrest has a higher rate of successful treatment that asystolic and electromechanical dissociation arrest ; the second scenario is much easier to remember as mnemonic, and is a more general framework for resuscitation from all causes , including primary airway obstruction causes, and hypoventilation/hypoxemia as a cause of unconsciousness.
DRABC is Danger Response, Airways, Breathing , Compression .
- remove from danger. Ensure your own safety - e.g. do not commence resuscitation in the middle of a undiverted road.
D could also be DELEGATE - initiate a PHONE call for help (in Australia, dial 000 for emergency ambulance)
or request another to get help. The RATIONALE for DELEGATE, is that in cardiac arrest where it is ventricular fibrillation, the most effective management is electrical defibrillation, available when the ambulance arrives.
check for consciousness - ask the patient to OPEN EYES and SQUEEZE MY HAND ,
and also SHAKE THE SHOULDERS if an uninjured adult, or if a child, or adult suspected of spinal injury,
apply PRESSURE STIMULUS ; anything less than or equal to a GROAN , is regarded as UNCONSCIOUSNESS. 
the aim is to open an obstructed , naturally positioned airway. In an uninjured adult, CHIN LIFT and HEAD TILT ; in injured adult or small child, CHIN LIFT only. an uninjured child may be SLIGHTLY TILTED, but AVOID PUSHING ON THE SOFT TISSUE OF THE NECK, and causing another source of obstruction.
CHIN LIFT can be achieved with - PINCER GRIP, PISTOL GRIP, or ANGLE OF JAW THRUST VERTICAL UPWARDS when the patient is lying horizontally face upwards (supine) (ANGLE OF JAW is where the angle of the L shape of the side profile of the jaw is)
The rationale behind CHIN LIFT, is that by lifting the jaw forwards, this pulls up the tongue away from the opening of the larynx, and opens up the collapsed larynx.
In practice, a successful airway management is when spontaneous breathing is heard with the ear placed over the mouth, or when artificial respiration results in the patient being heard to breath out again , and the chest move up and down.
CONSCIOUS SEVERE OBSTRUCTED AIRWAY (CHOKING WITH INEFFECTIVE COUGH)
INEFFECTIVE COUGH is where the patient appears not to be getting enough air between coughs, or is not coughing and not breathing and unable to speak.
This is managed by ALTERNATING 5 BACK BLOWS between the shoulder blades with the palm, with 5 STERNAL THRUSTS with the palm ; this is different from the Heimlich maneuver, which was thrusting the diaphragm upwards with a fist in palm hands , whilst holding the patient from behind and under the armpits ; this maneuver could cause internal organ injury, such as rupturing the spleen or liver . If the patient is UNCONSCIOUS and was CHOKING, commence CPR as Airways , Breathing , Circulation described here. 
The new recommendation is to give 2 rescue breaths ; if the rescuer is unwilling to give rescue breaths , mouth to mouth, with or without a separation device e.g. a pocket resuscitation mask, a piece of glad wrap with a central hole over the mouth opening, a piece of paper with a central hole over the mouth opening,
then it is still important to provide circulation as below, with or without attempted expired air resuscitation. ANY ATTEMPT AT RESUSCITATION IS BETTER THAN NONE; BUT CALL FOR HELP (DIAL 000) , SO THAT
DEFINITIVE THERAPY CAN BE GIVEN. ANY ATTEMPT IS BUYING MORE TIME FOR DEFINITE HELP TO ARRIVE.
It is this author's experience, that mouth-to-mouth resuscitation, whilst lifting the patient's chin, is MUCH EASIER than trying to ventilate the patient with a device such as a BAG AND MASK. The only thing easier to ventilate, is a CORRECTLY SITED TRACHEAL INTUBATED patient ( getting to that status though, is not easy).
The provision of artificial ventilation is probably the primary therapy for OPIATE OVERDOSE, other than administering an opiate antagonist, such as NALOXONE;
there are anecdotes of drug affected patients being kept alive till the drug overdose wears off , by other drug affected people with brains enough to provide expired air resuscitation , but still not responsible enough to seek hospital or ambulance help. It is probably on par with being responsible human beings as drug buddies that dump the ODed user at the front door of the casualty department or the GP clinic , after attracting the attention of the triage nurse/receptionist. Druggies can be heroes too ( like extreme sportsmen helping an injured fellow ?)
Like the above statement about resuscitation, ANY ATTEMPT TO REMOVE FROM DANGER IS BETTER THAN NONE.
Updated first aid guidelines for laypersons now downplay the significance of checking for a pulse, thus circulation. Laypersons are advised to commence CPR immediately should the victim not be breathing.
external cardiac compression is achieved by placing 2 hands palm downwards over the MIDDLE OF LOWER HALF OF THE STERNUM , and leaning one's whole upper body onto STRAIGHT ARMS HELD VERTICAL OVER THE PATIENT, and pushing down in a piston action, to a DEPTH of about 5 cm for adults, or
ONE-THIRD THE DEPTH OF THE CHEST.
In an INFANT, 2 FINGERS SHOULD BE USED INSTEAD.
THE RATE OF COMPRESSION IS 100 COMPRESSIONS PER MINUTE, for ALL AGE GROUPS.
SINCE THE RATIO OF COMPRESSION TO BREATHS GIVEN IS NOW 30 to 2 , THIS AMOUNTS TO ABOUT
3 CYCLES OF CPR PER MINUTE.
The old rate was 2:15 , but the time to change from giving ventilation to cardiac compression was a factor in decreasing the amount of compressions given in one minute; at 30:2 , there are half as many changeovers .