Defibrillator

Cardiac Arrest

An Elder Having a Cardiac Arrest.

If the heart stops beating properly and blood stops flowing due to various reasons, the brain starts to lose its oxygen supply and soon after death within five minutes. That's why people who suffer cardiac arrest (when their heart stops or goes into a dangerously abnormal rhythm) need emergency medical treatment. 


CPR (cardiopulmonary resuscitation) can help maintain the flow of oxygen to the brain, but getting the heart restarted and working normally often requires defibrillation with an electric shock.

CPR is given to a Cardiac Arrested Person.

Introduction.

As the name suggests, defibrillation stops fibrillation, the useless trembling that a person's heart muscles can adapt during a cardiac arrest. Simply speaking, a defibrillator works by using a high-voltage (something like 200–1000 volts) to pass an electric current through the heart so it's shocked into working normally again. The patient's heart receives roughly 300 joules of electrical energy.

The most common kind of defibrillator consists of an electric supply unit and two metal electrodes called paddles that are pressed very firmly to the patient's chest using insulating plastic handles (so the person using them doesn't get a shock too). The important thing is getting the current to flow through the heart, so where the paddles are applied is crucial.

One way of applying them is to put one paddle above and to the left of the heart and the other slightly beneath and to the right.

Another method involves placing one paddle on the front of the body and the other around the back.

In order for the electric current to flow properly, and to reduce the risk of skin burns, the electrodes have to be applied close enough together. They must also make good electrical contact with the skin, so a solid or liquid conducting gel is usually applied to the patient's chest first.

In units designed to be used by less-trained people in public places, sticky, self-adhesive electrode pads are often used instead of paddles for safety and simplicity: once the pads are stuck on, the operator can stand well clear of the patient's body and reduces the risk of their getting an electric shock.

A Defibrillator.

Types of defibrillators

Most defibrillators are energy-based, meaning that the device charges a capacitor to a selected voltage and then delivers a pre-specified amount of energy in joules. The amount of energy that arrives at the myocardium is dependent on the selected voltage and the transthoracic impedance (which varies by patient).

Mainly modern Defibrillators can be grouped into five categories:

1.  Advanced Life Support (ALS) Units
2. Automated External Defibrillators (AEDs)
3. Manual External Defibrillators (MEDs)
4. Implantable Cardioverter Defibrillators (ICDs)
5. Wearable defibrillators.

(ALS) units:- are used in the healthcare setting such as in hospitals and ambulances and allow staff to monitor the patient’s heart rhythm and intervene manually if a shock is required. The majority of these units contain an in-built function that uses advanced algorithms to perform waveform analysis and recommend the charge that should be used. Many ALS units are equipped with additional functions such as the monitoring of carbon dioxide and oxygen levels, blood pressure measurement, temperature monitoring, and a myocardial infarction alert system.

AEDs:- have self-adhesive electrode pads and a built-in computer that automatically analyzes the patient's heart rhythm to figure out whether a shock will help them (defibrillation doesn't work if the heart has stopped beating altogether) and, if so, what level of shock is appropriate.

AEDs can be further divided into two groups:  
The semi-automatic:- indicates the need for defibrillation but requires that the operator deliver the shock by pushing a button.
The fully automatic:- AED is capable of administering a shock without the need for outside interventions.

Comparison Between the Above Two.

Most current AEDs are energy-based but there are two other types of defibrillators less frequently used in clinical practice:-

• Impedance-based defibrillators:- allow selection of the current applied based upon the transthoracic impedance (TTI). TTI is assessed initially with a test pulse and subsequently the capacitor charges to the appropriate voltage. In patients with high TTI there was a significant improvement in shock success rate using this approach when compared to the energy-adjusting defibrillators.
• Current-based defibrillators:- deliver a fixed dose of current which results in defibrillation thresholds that are independent of TTI. The optimal current for ventricular defibrillation appears to be 30 to 40 amperes independent of both TTI and body weight thus achieving defibrillation with considerably less energy than the conventional energy-based method. Current-based defibrillation was proved superior to energy-based defibrillation with monophasic waveforms in one clinical study but this concept merits further exploration in the light of biphasic waveforms now available.   

Manual External Defibrillator (MEDs):- devices the doctors, nurses, or paramedics have to figure out whether defibrillation will help and also what shock voltage or energy level to use.

(ICDs):- units are placed directly into the chest of patients (a bit like a pacemaker) who are at high risk of sudden death, such as those with medical conditions known to put them at risk or patients who have already experienced ventricular fibrillation or ventricular tachycardia.

Wearable defibrillators:- are used for patients who are known to be at short-term risk of sudden death and for those who do not qualify as candidates for an ICD.

Waveforms and their importance Energy-based defibrillators can deliver energy in a variety of waveforms, broadly characterized as monophasic, biphasic, or triphasic.

Monophasic waveform:- Defibrillators with this type of waveform deliver current in one polarity and were the first to be introduced. They can be further categorized by the rate at which the current pulse decreases to zero. If the monophasic waveform falls to zero gradually, the term damped sinusoidal is used. If the waveform falls instantaneously, the term truncated exponential is used. The damped sinusoidal monophasic waveforms have been the mainstay of external defibrillation for over three decades.

Biphasic waveform:- This type of waveform was developed later. The delivered current flows in a positive direction for a specified time and then reverses and flows in a negative direction for the remaining duration of the electrical discharge. With biphasic waveforms, there is a lower defibrillation threshold (DFT) that allows reductions of the energy levels administrated and may cause less myocardial damage. The use of biphasic waveforms permits a reduction in the size and weight of AEDs.

Triphasic waveform: There are no human studies to support the use of multiphasic waveforms over biphasic. Investigation in animals suggests that the benefits of biphasic waveform could be harnessed through the use of a tri-phasic waveform in which the second phase has the larger strength to lower the DFT and the third phase has the lower strength, to minimize damage.

Waveform Patterns.

Major Parts of a Defibrillator.
1. Power Source:
There are two different types of power sources that can be used in defibrillators.

Power supply

Step-up transformers are used to convert the mains voltage of 240 V AC to 5000 V AC. This is then converted to 5000 V DC by a rectifier. In practice, a variable voltage step-up transformer is used so that different amounts of charge may be selected by the clinician. The control switch is calibrated in energy delivered to the patient (J) because this determines the clinical effect.

If a mains supply is unavailable, most defibrillators have internal rechargeable batteries. These supply DC, which is then converted to AC by means of an inverter, and then amplified to 5000 V DC by a step-up transformer and rectifier as above.

Batteries.

Essentially they are containers of chemical reactions and one of the most important parts of the AED system. Initially, lead batteries and nickel-cadmium were used but lately, non-rechargeable lithium batteries, smaller in size and with longer duration without maintenance (up to 5 years), are rapidly replacing them. Since extreme temperatures negatively affect the batteries, defibrillators must be stored in controlled environments.

Also, it is important to dispose of the batteries using designated containers as they contain corrosive and highly toxic substances.

2. Electrical circuit.

AEDs are highly sophisticated, microprocessor-based devices that analyze multiple features of the surface ECG signal including frequency, amplitude, slope, and wave morphology. It contains various filters for QRS signals, radio transmission, and other interferences, as well as for loose electrodes and poor contact. Some devices are programmed to detect patient movement.

3. Capacitors

The most important component of a defibrillator is a capacitor that stores a large amount of energy in the form of electrical charge, then releases it over a short period of time. The capacitors which are used here can hold up to 7 kV of electricity and can deliver energy in between 30 to 400 joules at a time with a peak value of current 20A.

4. Inductors

For successful defibrillation, the current delivery must be maintained for several milliseconds. However, the current and charge delivered by a discharging capacitor decay rapidly and exponentially. Inductors are therefore used to prolong the duration of the current flow. They are coils of wire that produce a magnetic field when current flows through them.

5. Electrodes

These are the components through which the defibrillator collects information for rhythm analysis and delivers energy to the patient's heart. Many types of electrodes are available including hand-held paddles, internal paddles, and self-adhesive disposable electrodes. In general, disposable electrodes are preferred in emergency settings because they increase the speed of shock and improve the defibrillation technique.

6. Controls.

The typical controls on an AED include a power button, a display screen on which trained rescuers can check the heart rhythm, and a discharge button. Defibrillators that can be operated manually have also an energy select control and a charge button. Certain defibrillators have special controls for internal paddles or disposable electrodes.

Intrathoracic Impedance.

Successful defibrillation depends on the delivery of the electrical charge to the myocardium. Only part of the total current delivered (about 35 A) flows through the heart. The rest is dissipated through the resistance of the skin and the rest of the body. The impedance of skin and thoracic wall act as resistances in series, and the impedance of other intrathoracic structures act as resistances in parallel with the myocardium. The total impedance is about 50 – 150 Ω, however, repeated administration of shocks in quick succession reduces impedance.

Principle of Defibrillation

Defibrillation is the definitive treatment for life-threatening cardiac arrhythmias ventricular fibrillation and pulseless ventricular tachycardia. Defibrillation consists of delivering a therapeutic dose of electrical energy to the affected heart with a device called a defibrillator. This depolarizes a critical mass of the heart muscle, terminates the arrhythmia, and allows normal sinus rhythm to be re-established by the Sinoatrial node.

Defibrillators can be external, wearable, or implanted, depending on the type of device used, but all operate on the same principle. A ventricular arrhythmia is detected by the monitoring circuit of the device. A capacitor is charged with an appropriate level of voltage for the device (either by an operator or automatically) and upon initiation of the shock (automatically or upon the press of a button) current is delivered directly to the heart to interrupt the arrhythmia and restore normal conduction. When the current is delivered via an internal defibrillator far less is required as there is not a lot of resistance in the circuit. External defibrillators, however, have to be able to deliver sufficient current to reach the heart through the mass of skin, hair, and tissue.

Until recently, most external defibrillation shocks were delivered via paddles placed upon the patient’s chest and the waveform was monophasic: Current traveled in one direction through the heart (monophasic waveform).

Monophasic (As the Arrow Shows; From above OR From Below).

Nowadays two major changes have occurred in defibrillation techniques:-

The first one is that the majority of defibrillation shocks are delivered through defibrillation electrodes, pads that are placed directly on the patient’s skin. These defibrillation pads are safer for rescuers, and because they conform to the chest are generally able to deliver the current more effectively.

The second major change in defibrillation is the use of biphasic waveform to deliver the current to the heart. With a biphasic waveform, the current is delivered to the heart in two vectors. Because of the two-vector approach, the peak current required to convert the arrhythmia is reduced, and the efficacy of the shock is greatly enhanced. It is generally accepted that biphasic defibrillation results in less myocardial damage from the shock itself.

Monophasic Vs Biphasic.

Pad Placement Methods

Placing Pads in Two Ways.

Safety

• Before administering the charge, it is essential to make the correct diagnosis to avoid defibrillating a patient who is already in sinus rhythm. 

• If a defibrillator monitor is being used, check that the leads are correctly connected and whether the device is monitoring from the paddles or from chest electrodes.

• The paddles should be placed across the long axis of the heart to facilitate effective defibrillation.

• The paddles should not be placed over transdermal patches, because they may block current delivery or if they contain an inflammable substance (e.g. glyceryl trinitrate) may result in burns or explosions.

• The paddles should not be placed near metal objects, either on the surface of the skin (e.g. ECG leads or electrodes, skin clips, jewelry), or subcutaneously (e.g. implanted pacemakers), because the current follows the path of least resistance through the metal, resulting in arcing, heating or burns.

• The paddle size should be appropriate for the patient (typically 13 cm diameter for adults): large enough to prevent burns but small enough to deliver an adequate current density.

• Conductive gel pads and firm pressure (about 10 kg force) are used to improve electrical contact between the paddles and the patient’s chest. Liquid electrode gel should not be used, because excess may cause arcing across the surface of the chest wall or the operator’s hands.

• All sources of oxygen must be removed from the patient during defibrillation because it supports combustion if arcing occurs.

• Staff should not touch the bed, patient, or any equipment connected to the patient during defibrillation.

• Fluids may conduct electricity, therefore it is important to ensure that the immediate area is clean and dry. 

• The defibrillator should not be charged until the paddles are applied to the patient’s chest, because accidental discharge from open paddles may cause injury or death.

• The operator must not touch any part of the paddle electrodes. Before administering the charge, the operator must shout “Stand clear!” and check that all staff has done so.

• If the defibrillator is charged but a shock is no longer indicated, it should be discharged through the defibrillator internally by turning the control knob to zero before removing the paddles from the patient’s chest: charged paddles should never be returned to the defibrillator.

• Equipment that does not have the ‘defibrillator protected’ symbol should be disconnected from the patient before defibrillation to prevent damage, heating, or arcing effects.

• The defibrillator should never be discharged with the paddles shorted together, as this may cause burning and damage to the electrical contacts.

Defibrillator Precautions

1. First of all, check the patient for a pulse. If you cannot sense the pulse you may proceed, and let the AED determine if there are heartbeats at all. In most of cases, the AED will indicate if there is a pulse and if defibrillation is needed.

2. You might want to try to perform cardiopulmonary resuscitation (CPR) before taking any further action. But make sure that the AED device is not analyzing the rhythm. This may cause some unpleasant accidents. Many AED devices possess motion and CPR detectors, but you won't have time to determine that in a crisis.

3. The AED device should be used with great care if the patient is in a moving means of transportation. The movement of a vehicle may affect the analysis the AED makes, which won't be accurate and consequently, it will perform incorrect tasks. However, if employed while transporting the patient to the hospital, stop and take the pulse several times and do monitoring checks with the help of the AED. Some AED models are smart enough to distinguish between external movement and cardiac movement.

4. Beware of water: Before performing the defibrillation, make sure the chest of patient is completely dry. In the AED kit, you will find a piece of cloth or a towel that is set there exactly with the purpose of drying the patient's chest. Sweat or water spots make certain parts of the chest be less resistant and defibrillation might not be very effective. Besides, the presence of water may lead to local burns. Also, make sure that the patient has no contact with water. If the patient is in a pool or outside, in wet weather, take the patient under a safe shelter and dry the chest before taking any further action. However, do not use alcohol to dry the chest of the patient. As you may probably know, alcohol is very flammable.

5. Take a close look at the patient's chest. It should be free of nitroglycerine patches or any other patches or materials. Get rid of any patches before performing the defibrillation. The nitroglycerine patches may cause an explosion when in contact with the AED pads.

6. Make sure the patient does not lie on a conductive surface like sheet metal or metal bleachers. These conductors may transmit the shock to other people that are in the patient's neighborhood.

7. Keep your hands off the patient while performing the defibrillation: Also make sure no one else touches the patient. If these rules are not respected, you or others might get an electric shock. Touching the patient while the AED performs the analysis will not give accurate results.

8. An AED should not be used on children under the age of 8, or under 55 pounds: Some AEDs are not able to adjust to the low-energy settings that are required for children. Anyway, there are several AED devices on the market that may resuscitate even children under 8. So check the packaging of the device before using it.

9. Take a look at the environment where you will perform the resuscitation: You shouldn't perform defibrillation if you are among flammable supplies such as gasoline or free-flowing oxygen. Also, the AED should be used with prudence when there is strong electromagnetic interference (EMI). The AED might detect false cardiac rhythms when there is electromagnetic interference.

10. Careful with the cell phones and portable radios- the waves cause trouble: It is highly important to notify an ambulance of the incident and the cell phone is the most effective device, but make sure you keep all cell phones at least 6 feet away from the patient and the AED. The cell phone may influence the analysis. Radios have the same effect on the AED, so keep all radios away.

Troubleshooting Tips for Defibrillation:

Some Troubleshooting Techniques.

   

👉 Please Watch Our Defibrillator Videos (Part 1 & Part 2) from Our YouTube Channel Below:-

1. Part 1 Video:-

2. Part 2 Video:-

Article Prepared By:-

👉 Gaston Ravin Dias 

References:

• Cardiac Defibrillator Devices - Defibrillator Models for CPR Resuscitation - Cardiac Resuscitation Devices. 2017. Cardiac Defibrillator Devices - Defibrillator Models for CPR Resuscitation - Cardiac Resuscitation Devices. [ONLINE] Available at: https://www.zoll.com/medical-products/defibrillators/. [Accessed 08 November 2017].
• Defibrillator - what is it and how to use it - British Heart Foundation . 2017. Defibrillator - what is it and how to use it - British Heart Foundation . [ONLINE] Available at: https://www.bhf.org.uk/heart-health/how-to-save-a-life/defibrillators. [Accessed 08 November 2017].
• Explain that Stuff. 2017. How do defibrillators work? - Explain that Stuff. [ONLINE] Available at: http://www.explainthatstuff.com/defibrillators.html. [Accessed 08 November 2017].
• Implantable Cardioverter Defibrillator (ICD). 2017. Implantable Cardioverter Defibrillator (ICD). [ONLINE] Available at: http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/Implantable-Cardioverter-Defibrillator-ICD_UCM_448478_Article.jsp#.WgKdR2iCzIU. [Accessed 08 November 2017].
• News-Medical.net. 2017. What is a Defibrillator? . [ONLINE] Available at: https://www.news-medical.net/health/What-is-a-Defibrillator.aspx. [Accessed 08 November 2017].
• Pacemakers and Implantable Defibrillators | MedlinePlus. 2017. Pacemakers and Implantable Defibrillators | MedlinePlus. [ONLINE] Available at: https://medlineplus.gov/pacemakersandimplantabledefibrillators.html. [Accessed 08 November 2017].
• What Is an Automated External Defibrillator? - NHLBI, NIH. 2017. What Is an Automated External Defibrillator? - NHLBI, NIH. [ONLINE] Available at: https://www.nhlbi.nih.gov/health/health-topics/topics/aed. [Accessed 08 November 2017].