An automated external defibrillator sends a controlled electrical charge to the heart. This interrupts the chaotic signals, causing cardiac arrest. It helps the heart regain its natural rhythm, lowering the risk of sudden death. The energy strength is adjusted based on the device’s waveform and the patient’s resistance. This ensures the shock is safe and effective.
Restoring a stable heart rhythm might need more than one shock. Sometimes, medications are also needed to help with recovery. Understanding how defibrillator voltage can reverse cardiac arrest is key. It also shows why adjusting energy levels matters. This highlights the precision needed for effective treatment.
Voltage, Current, Impedance, and Energy Delivered (in joules)
For many, electricity is best understood as voltage. It is often used to explain the power from batteries and outlets.
In the early days of automated external defibrillators, people used voltage to measure the first defibrillation attempts.
- In 1947, Claude Beck revived a 14-year-old patient. He used four 110-volt direct-current shocks through electrodes during open-heart surgery.
- In 1956, Paul Zoll developed a closed-chest defibrillation method. This technique can deliver shocks up to 750 volts safely. This means open-heart surgery may not be needed.
- In 1957, William Kouwenhoven at Johns Hopkins University made a 250-pound “portable” external defibrillator. It could deliver 480-volt alternating current shocks to treat adult patients safely.
Early defibrillation used volts for shocks. Now, modern automated external defibrillators (AEDs) use joules. This change shows the real energy given to the heart.
Voltage Explained
Within the International System of Units (SI), voltage is formally defined as:
- Electrical potential
- Electrical potential difference
- Electromotive force
As described in the Encyclopaedia Britannica entry on volts:
One volt is the electric potential difference between two points. It occurs when a current of one ampere leads to a power output of one watt. This is the same as the voltage across a one-ohm resistor with that current.
The power from a 9-volt battery changes based on the resistance between the battery and the heart. This resistance affects how much energy is transferred.
Voltage alone doesn’t fully explain how it affects the heart. It shows the electrical potential in a circuit. The key factor is the current flowing through the heart muscle. That’s why modern defibrillators use various measurements to show this effect better.
Current Explained
Electrical current, measured in amperes, is the flow of electric charge in a circuit.
An ampere is the flow of one coulomb of electric charge each second. A potential difference of one volt drives this flow through a one-ohm resistance.
A current of about 100 milliamperes can disrupt heart function. This is why electric fences use high voltage with very low current. It helps reduce the risk of fatal injury if someone contacts them.
Joules and Impedance
In defibrillation, impedance is measured in ohms. It impacts how much current gets to the heart. Higher impedance limits the flow because it increases resistance in the body.
Automated external defibrillators (AEDs) deliver a shock by checking the resistance between the electrode pads. They change the energy in joules to ensure enough current flows through the heart, despite the resistance.
By definition:
A joule is the energy used when one watt of power acts for one second. For example, it’s what happens when a one-ampere current passes through a one-ohm resistance.
How Many Joules Are Delivered with Each Shock to the Heart?
Biphasic defibrillators usually start between 120 and 200 joules. They begin at lower energy levels and go up if needed. Studies show that higher-energy biphasic shocks don’t harm the heart more than lower doses do. However, using less energy can lead to fewer skin burns and better recovery in some cases.
Modern internal and external defibrillators use biphasic shocks. These shocks treat shockable rhythms effectively and at lower energy levels. This is a change from older monophasic systems, which needed higher-energy shocks.
Shock Energy Sequence Examples
Devices like the Philips HeartStart FRx and Defibtech Lifeline use a biphasic waveform. They deliver about 150 joules for adults and 50 joules for children. This is based on a standard impedance of 50 ohms.
The HeartSine Samaritan PAD 350P, HeartSine Samaritan PAD 360P, and HeartSine Samaritan PAD 450P utilize a proprietary SCOPE™ technology to deliver controlled levels of energy.
- 150 J for the first shock, 150 J for the second shock, and 200 J for the third shock in adults
- 50 J for the first shock, 50 J for the second shock, and 50 J for the third shock in children
These models come with default energy levels from the factory. They adjust the shock delivered based on the patient’s impedance.
The Philips HeartStart FRx changes its output based on resistance. It delivers about 128 joules at low impedance and up to 158 joules at higher levels. Pediatric doses are also adjusted to fit these impedance conditions.
Defibrillation impedance can be affected by several factors. Chest hair, body composition, and equipment issues can all block current flow. To improve conduction, electrode pads use a conductive adhesive. This creates a direct path to the heart. It’s important to use fresh pads, dry the skin, and remove excess hair before applying them.
How Long Each Shock Lasts
The shock feels intense, but it lasts a fraction of a second. There’s only a tiny gap between the two phases of the pulse.
The duration of each shock phase depends on patient impedance. For adults, it usually lasts a few milliseconds. In children, the intervals are often shorter. Devices like the HeartSine Samaritan PAD 350P keep a consistent 0.4-millisecond pause between phases. This happens no matter the impedance.
Battery Voltage, Shocks Delivered, and Most Operating Time
Modern automated external defibrillators use small 9-volt batteries. This keeps them lightweight and easy to carry in emergencies.
The Philips HeartStart FRx uses a sealed 9-volt lithium manganese dioxide battery. This battery can deliver up to 200 shocks or run for about four hours in normal conditions.
The HeartSine Samaritan PAD 350P has an 18-volt lithium manganese dioxide battery. This battery includes the electrode cartridge. It provides over 60 shocks or six hours of monitoring when new. Even after years of use, it can still deliver multiple shocks.
The Defibtech Lifeline DCF-100 has a 9-volt lithium battery for regular self-testing. For longer use, you can choose optional high-capacity lithium manganese dioxide battery packs.
- The DBP-1400 battery pack has 15 volts and 1400mAh of power, a capacity of 125 shocks or eight hours of continuous operation, and a standby life of five years.
- The DBP-2800 battery pack has 15 volts and 2800mAh of power, a capacity of 300 shocks or 16 hours of continuous operation, and a standby life of seven years.
Automated external defibrillators have changed a lot since the 1950s. Back then, “portable” units were bulky and weighed 250 pounds.
A Note About Manual Defibrillator Shock Energy…
Most modern manual defibrillators, like automated external ones, use biphasic shocks. These shocks are measured in joules. Clinicians can change the energy level on manual devices. In contrast, automated devices calculate it on their own.
Manual defibrillators offer precise control over shock levels. This makes them ideal for infants needing low energy doses. Only trained advanced cardiac life support professionals can use them. This includes doctors and paramedics.
How Defibrillators Deliver an Electrical Shock
Automated defibrillation involves a basic three-step process.
Step 1: Cardiac Rhythm Analysis
After you put the electrode pads on bare skin, the defibrillator looks at the heart’s electrical activity. It decides if a shock is needed. It’s important not to touch the patient during this time to avoid interference.
Shockable Rhythms
The two AED shockable rhythms are:
- Ventricular fibrillation (v-fib)
- Pulseless ventricular tachycardia (v-tach)
These irregular rhythms can be fixed with a shock. The heart still has electrical activity, even if it’s disorganized. The defibrillator stops this chaotic signaling for a moment. This lets the heart return to a normal rhythm.
Non-Shockable Rhythms
Some heart rhythms can’t be treated with a shock. For example, in asystole, there is no electrical activity. In pulseless electrical activity, signals look organized but don’t create a pulse. Here, defibrillation won’t work because there’s no chaotic activity to reset.
Step 2: Shock Advised or Shock Not Advised
The AED checks the heart. If a shock is needed, it uses battery power to charge up for delivery. During this process, the device may show its charging status. It usually takes a few seconds to gather enough energy based on the chosen shock level.
When the charge is ready, the device delivers the shock automatically. Otherwise, it tells the rescuer to press a button. It checks first to make sure no one is touching the patient. If a shock isn’t delivered within a short time or the rhythm changes, the stored energy is safely discharged.
Step 3: Resume CPR
After delivering the shock, the AED signals it’s safe to touch again. It then guides rescuers to start CPR. Trained people should do standard compressions with breaths. Others can perform hands-only compressions.
The device checks the heart rhythm every two minutes. It decides if another shock is needed. Keep the pads in place, even if no shock is advised. The AED will track the heart. It can respond if the rhythm becomes treatable before help arrives.
Importance of the Voltage of a Defibrillator for Lay Rescuers and AED Program Managers
Understanding how voltage, current, and energy work in defibrillation is important. It shows key points for AED program managers and responders.
- Do not touch the patient when the AED says “stand clear”! The body conducts electricity. Any contact with the patient during analysis or shock delivery can disrupt treatment. It can also transmit the shock to others, even through nearby objects like metal.
- Remove medicated patches before placing the pads. Adhesive medicated patches, like nicotine patches, can block electrical flow. This can raise the risk of burns by pushing the device to deliver extra energy. So, remove the patches and clean the skin before applying the pads.
- Don’t place the pads directly over a pacemaker or implantable cardioverter defibrillator. Implanted devices such as pacemakers or ICDs can disrupt current flow. A shock may harm them. So, place pads a few inches away or use a different configuration.
- Shave excessive chest hair. Excess chest hair can hinder pad adhesion. This increases resistance and reduces current flow. So, it should be removed quickly before placing the pad. This ensures a safe and effective shock.
Electricity, when properly delivered, can reverse common arrhythmias of cardiac arrest
An AED can deliver a shock in volts, amperes, or joules. This shock can disrupt dangerous heart rhythms. It greatly boosts a cardiac arrest victim’s chance of survival.
Defibrillation doesn’t work for everyone. Patients still need advanced medical care. Using an AED early, along with good CPR, gives the best chance for survival and recovery after cardiac arrest.
References:
- Skin Reactions Following Defibrillation or Cardioversion; Physio-Control White Paper; 1995
- The effects of biphasic and conventional monophasic defibrillation on postresuscitation myocardial function; Journal of the American College of Cardiology; September 1999
Information Sources
FAQs
What is the defibrillator voltage in an Automated External Defibrillator?
Defibrillator voltage is the shock’s electrical potential. Modern automated external defibrillators (AEDs) measure energy in joules for effective treatment.
How many volts are in AED devices?
The voltage in an AED can change. It automatically adjusts its output based on the patient’s impedance. This way, it focuses on giving the right energy instead of a set voltage.
Why is defibrillator voltage important during resuscitation?
Defibrillator voltage helps create the current to reset the heart. However, the main factor is providing the right energy for effective defibrillation.
What is the typical voltage for defibrillator shocks?
The voltage for defibrillator shocks varies. It depends on the device and the patient’s condition. Modern AEDs adjust the output automatically.
How does the Automated External Defibrillator voltage differ from joules?
Automated external defibrillators use voltage to represent electrical potential. Joules are used in practice since they measure the energy delivered to the heart.
Does the AED voltage change based on the patient?
Yes, the AED adjusts its voltage based on patient impedance. This change delivers the right current to the heart for effective treatment.
Conclusion
In summary, knowing defibrillator voltage is helpful. However, modern resuscitation aims to deliver the right energy to the heart. Automated external defibrillators analyze heart rhythms. They adjust output based on patient impedance. Then, they deliver shocks to restore a normal heartbeat. Timely intervention is what counts most. Voltage, current, and energy also matter, but not as much. Using an AED, quick responses, and good CPR greatly boosts survival rates in sudden cardiac arrest.
