Defibrillator
From Simple English Wikipedia, the free encyclopedia
 |
The English used in this article may not be easy for everybody to understand. You can help Wikipedia by making this page or section simpler. |
A defibrillator is a medical device that is used to defibrillate the heart. It does this by shocking the heart with an electric current to stop ventricular fibrillation or pulseless ventricular tachycardia. The current is sent through two electrodes. These electrodes are normally either paddles or sticky pads. Each electrode is placed on one side of the heart.
Ventricular fibrillation is a situation of electrical chaos in the heart's conduction system. It changes the normal contractions of cardiac muscular tissue. This causes the heart to stop pumping blood around the body properly. It causes circulatory arrest and death within minutes from hypoxic brain damage. The electric current from a defibrillator stops all electrical activity in the heart by depolarising its electrical system. This lets the hearts normal impulses regain control of the muscular tissue of the heart.
Contents |
[edit] Types of defibrillators
[edit] Internal defibrillators
Implantable cardioverter-defibrillators (ICD) are defibrillators that are designed to defibrillate patients from inside their body. They are put inside people that are at high-risk of going into cardiac arrest and monitor a person's heart rate, rhythm, and waveform, and by comparing atrial and ventricular activity, an implantable cardioverter-defibrillator can detect cardiac arrhythmias and treat them quickly.
[edit] External defibrillators
External defibrillators are often used in hospitals and ambulances, but they are now being used outside of medical environments more as automated external defibrillators become safer and cheaper. There are a variety of technologies and form factors in use for external defibrillators, and recent progress in cardiac research has led to big improvements in the underlying technology.
[edit] Biphasic defibrillation
Until recently, external defibrillators relied on monophasic shock waves. Electrical pulses are quickly sent from one electrode to the other in one direction. Biphasic defibrillation, however, alternates the direction of the pulses, completing one cycle in approximately 10 milliseconds. Biphasic defibrillation was originally developed and used for implantable cardioverter-defibrillators. When applied to external defibrillators, biphasic defibrillation significantly decreases the energy level necessary for successful defibrillation. This, in turn, decreases the risk of burns and other damage. However, there is limited evidence to suggest that biphasic defibrillation is better than monophasic defibrillators, although the small capacitor size required for the defibrillator can result in significant cost and size savings -- essential for the proliferation of automated external defibrillators.
[edit] Automated external defibrillators
An automated external defibrillator (AED) is a self-contained defibrillator device designed to be movable easily and simple to use. They are often shaped like briefcases so that they can be carried by a handle. An automated external defibrillator contains a battery, a control computer, and electrodes. When the electrodes are stuck onto the patient, the control computer will assess the patient, checking the rhythm of their heart. It will then charge itself to an appropriate power level and tell users that the person needs to be shocked. If the patient does not need to be defibrillated, the automated external defibrillator will not allow a shock to be administered. A button must still be pushed manually to trigger the shock, as the operator beforehand must be certain that nobody is touching the patient. Often, automated external defibrillators will have speakers which give instructions when they are opened.
Current automated external defibrillator devices are designed for emergency medical technicians, home users, public safety officers and other people with minimal medical knowledge. AEDs are available for $1000 for a basic model to several thousand dollars for a more fully-featured or durable model.
These devices are commonly found in large gathering places, such as airports, casinos, sports stadiums, and college campuses.
[edit] Electrodes
The electrodes are a key part of a defibrillation system.
[edit] Design
The most well-known type of electrode is the traditional metal paddle with an insulated handle. This type must be held in place on the patient's skin while shocks are delivered. Before the paddles are used, gel must be applied to the patient's skin so that there is a good connection and to minimise electrical resistance, also called chest impedance (despite the direct current discharge).
Another type of resuscitation electrode is designed as an adhesive pad. When a patient has been admitted due to heart problems, and the physician or nurse has determined that he or she is at risk of arrhythmia, they may apply adhesive electrodes to the patient in anticipation of any problems that may arise. These electrodes are left connected to a defibrillator. If defibrillation is required, the machine is charged, and the shock is delivered, without any need to apply any gel or to retrieve and place any paddles.
Both solid- and wet-gel adhesive electrodes are available. Solid-gel electrodes are more convenient, because there is no need to clean the patient's skin after removing the electrodes. However, the use of solid-gel electrodes presents a higher risk of burns during defibrillation, since wet-gel electrodes more evenly conduct electricity into the body.
While paddles on a monitor/defibrillator may be quicker than using adhesive pads, pads are superior due to their ability to provide appropriate electrocardiogram readings without the artifact visible from human interference with the paddles. Many monitor defibrilators provide three, five or 12-lead ECG monitoring to compensate for this downfall of the paddles. Adhesive electrodes are also inherently safer than the paddles for the operator of the defibrillator to use, as they minimize the risk of the operator coming into physical (and thus electrical) contact with the patient as the shock is delivered, by allowing the operator to stand several feet away. Another inconvenience of the paddles is the requirement of around 11 kilograms of pressure to be applied while defibrillating.
[edit] Placement
Resuscitation electrodes are placed according to one of two schemes. The anterior-posterior scheme is the preferred scheme for long-term electrode placement. One electrode is placed over the left precordium (the lower part of the chest, in front of the heart). The other electrode is placed on the back, behind the heart in the region between the scapula. This placement is preferred because it is best for non-invasive pacing.
The anterior-apex scheme can be used when the anterior-posterior scheme is inconvenient or unnecessary. In this scheme, the anterior electrode is placed on the right, below the clavicle. The apex electrode is applied to the left side of the patient, just below and to the left of the pectoral muscle. This scheme works well for defibrillation and cardioversion, as well as for monitoring an ECG.
