If someone drops dead, it is most commonly a cardiac arrest. It happens because the heart, instead of pumping blood in normal rhythmic fashion, suddenly stops beating regularly and instead, quivers or shivers- called ventricular fibrillation. Blood supply to vital organs like the brain stops and in less than 10 minutes there is certain death.

How does one recognize a cardiac arrest? 

First, call the affected person in a loud voice. If there is no response, shake the person to check if he or she is conscious. If there is no response, check the breathing: Is it normal or abnormal? Abnormal breathing means either no breathing at all or intermittent gasping. If you witness a person suddenly collapse for no apparent reason and that person is unresponsive and not breathing normally, you should treat this as a cardiac arrest. Do not waste time trying to determine whether the victim has a pulse.

What should one do?

First call for the cardiac ambulance. The only way the quivering heart will start beating normally is by giving an electric shock to it. It is done by a gizmo called defibrillator. Modern cardiac ambulances are equipped with it and paramedics can give it. However, till the time the shock is given you have to keep the blood moving to vital organs like the brain.  Hence the next important and fast step is to start CPR or cardio pulmonary resuscitation. 

And here comes AHA! the good news! 

Till now, the standard way of giving CPR was giving chest compressions interrupted by mouth to mouth breathing in a 30 to 2 ratio. However, according to a new "science advisory" statement from the American Heart Association (AHA)—mouth to mouth breathing doesn't necessarily improve outcomes after cardiac arrest.

It has been found that survival chances for adult victims of out-of-hospital collapse dueto cardiac arrest are same (or even better) if they receive hands-only (compression-only) CPR without mouth to mouth breathing as compared to conventional CPR with mouth to mouth breathing. Hence, it says, continuous chest compressions without mouth to mouth breathing is at least as good a method of CPR as standard CPR with mouth to mouth breathing for this group of patients, especially by lay people untrained in standard CPR.

This has tremendous public health importance. Firstly, it makes things simpler to follow for lay people and secondly it removes the fear of infections related to mouth to mouth breathing. Thus there will be more willingness from untrained bystanders to act promptly.

However, certain caveats to this new advisory should be noted:

For a rescuer trained in CPR or who is "confident in his or her ability to provide rescue breaths with minimal interruptions in chest compressions," either compression-only or conventional CPR, with a ratio of 30 chest compressions to 2 ventilations, is recommended.

Also, the new recommendation for bystander intervention "does not apply to unwitnessed cardiac arrest, cardiac arrest in children, or cardiac arrest presumed to be of noncardiac origin." like drowning, trauma, airway obstruction, acute respiratory diseases, and stoppage of breathing (apnea) such as that associated with drug overdose which will need standard CPR with mouth-to-mouth breathing.

So, if you witness an adult who collapses for no apparent reason and that person is unresponsive and not breathing normally first call for help (see figure).

• Then position the patient on the floor, face up.
  
  
• Place the heel of one hand on the center of the chest with the heel of the other hand on top of the first. Lock your elbows so that your arms are straight.
  
  
• Position your shoulders directly above the center of the patient’s chest and fall so that the weight of your upper body compresses the patient’s chest.
  
  
• Perform fast, forceful chest compressions at about 100/min, compressing the chest 1.5 to 2 in.
  
  
• Lift hands slightly after each compression to allow the chest to recoil.
  
  
• Continue till the paramedics or the patient (if revived) tell you to stop or you are too tired to continue.

Photo credit to: The University of Arizona Sarver Heart Center