CPR (Cardiopulmonary resuscitation) is an emergency procedure for manually preserving the blood circulation of a person in cardiac arrest. Cardiac arrest means that the normal circulation of blood has stopped due to failure of a normal heart function, typically that the heart fails to contract effectively.
Lack of blood circulation is critical since delivery of oxygen to the body is prevented. Lack of oxygen to the brain is very critical and will cause loss of consciousness, which in turn will result in abnormal or absent breathing. If cardiac arrest is not treated within five minutes brain damage will most likely follow.
CPR generally involves chest compressions at least 5 cm deep and at a rate of at least 100 per minute in an effort to create artificial circulation by manually pumping blood through the heart. CPR is often combined with electric shock treatment by performing defibrillation.
Defibrillation includes delivering a therapeutic dose of electrical energy to the heart with a device called a defibrillator. The purpose is to restore a normal heart rhythm by depolarizing a critical mass of the heart muscle. Defibrillators can be external or implanted, depending on the type of device used or needed. Some external units, known as automated external defibrillators (AEDs) automate the diagnosis such that lay responders or bystanders are able to use them successfully with little or no training at all.
The connection between a defibrillator and a patient consists of a pair of electrodes that are placed on the patient such that an electric shock passes through the heart muscle.
FIG. 1 is an illustration showing a typical electrode placement on a body 10 used during defibrillation where one electrode 100, 105 is placed on each side of the heart 110 such that the electric shock 115, symbolized as dashed lines, will pass through the heart.
Applying electric shock to a body is well known, but knowing if the body actually has received an electric shock and the efficiency of this without measuring this directly in the body is not known.
Even if a defibrillator indicates that a shock has been given it does not guarantee that the shock has been applied to a patient. There is a risk of causing injury to a patient when using a defibrillator. This is due to possible electrical resistance between electrodes and body resulting in possible burning of a patient. Minimization of electrical resistance for decreasing the impedance to a chest is normally done by using electricity conductive gel.
Knowing that a shock has been applied to a patient is thus an important factor when considering further application of shock treatment.