An automated external defibrillator (AED) gives a controlled electric shock to the heart. This shock helps stop chaotic electrical activity during cardiac arrest. Stopping these irregular impulses helps the heart reset. This leads to a normal rhythm and greatly boosts survival chances. The energy level changes with the device’s waveform and the patient’s body resistance. This way, each shock is safe and effective.
Restoring a normal heart rhythm often needs several shocks. Sometimes, supportive medications help improve the results. Defibrillator voltage plays a key role in reversing cardiac arrest. Properly adjusted energy levels make the treatment precise and effective.
Voltage, Current, Impedance, and Energy Delivered (in Joules)
Electricity is often described by voltage. Voltage shows the force that drives electric current. This idea often means energy from common sources like batteries and power outlets.
In the early days of automated external defibrillators, people often measured initial shocks in voltage.
- 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 defibrillators used voltage to describe shocks. Now, modern automated external defibrillators measure output in joules. This shows the real energy delivered to the heart.
Voltage Explained
In the International System of Units (SI), voltage is officially described as follows:
- Electrical potential
- Electrical potential difference
- Electromotive force
As described in the Encyclopaedia Britannica entry on volts:
A volt measures the electric potential difference between two points. If a current of one ampere flows, it produces one watt of power. This is equal to the voltage across a one-ohm resistor in the same situation.
The energy from a 9-volt battery changes based on the resistance between it and the heart. This resistance affects how much power is transferred.
Voltage alone doesn’t show its full effect on the heart. It indicates the electrical potential in a circuit. The key factor is the current flowing through the heart muscle. That’s why modern defibrillators use extra measurements for better accuracy.
Current Explained
Electrical current, measured in amperes, is the flow of electric charge in a circuit.
An ampere is one coulomb of charge moving each second. This happens when there’s a one-volt potential across a one-ohm resistance.
A current of about 100 milliamperes can disrupt heart activity. That’s why electric fences use high voltage with low current. This design helps reduce the risk of serious harm if someone touches it.
Joules and Impedance
In defibrillation, impedance is measured in ohms. It affects how much current reaches the heart. Higher resistance means less current flows through the body.
Automated external defibrillators adjust the shock based on the pad resistance. This ensures they deliver enough energy in joules. That way, the needed current flows through the heart effectively.
By definition:
A joule is the energy used when one watt of power works for one second. For example, it happens when a one-ampere current goes through a one-ohm resistor.
How Many Joules Are Delivered with Each Shock to the Heart?
Biphasic defibrillators usually give initial shocks of 120 to 200 joules. They only raise the energy if needed. Research shows that higher levels don’t lead to more heart damage. However, lower doses might lessen skin injury and help recovery in some cases.
Modern defibrillators, whether internal or external, use biphasic shocks. These shocks effectively treat shockable rhythms with lower energy levels. This shows a change from older monophasic devices. They needed much more energy to get similar results.
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 devices come with standard energy levels. They automatically adjust the shock based on the patient’s impedance.
The Philips HeartStart FRx adjusts its energy delivery based on resistance. It gives about 128 joules at lower impedance and up to 158 joules at higher resistance. It also changes pediatric doses to fit these settings.
Defibrillation impedance can be affected by several factors. These include chest hair, body composition, and equipment limitations. Each of these can restrict current flow. Electrode pads have a conductive adhesive for better contact and a clear path to the heart. For effective conduction, follow these steps: use fresh pads, dry the skin, and remove extra hair.
How Long Each Shock Lasts
The shock is quick but strong. It lasts a split second, with little gap between the two pulse phases.
The length of each shock phase changes with patient impedance. In adults, it usually lasts a few milliseconds. In children, it’s often a bit shorter. Devices like the HeartSine Samaritan PAD 350P keep a steady 0.4-millisecond gap between phases, no matter the resistance.
Battery Voltage, Shocks Delivered, and Most Operating Time
Modern automated external defibrillators use small 9-volt batteries. This makes them lightweight and easy to carry for emergencies.
The Philips HeartStart FRx uses a sealed 9-volt lithium manganese dioxide battery. This battery can provide up to 200 shocks or last about four hours in normal use.
The HeartSine Samaritan PAD 350P has an 18-volt lithium manganese dioxide battery. This battery is built into the electrode cartridge. It provides over 60 shocks or up to six hours of monitoring when new. Even after heavy use, it can still deliver multiple shocks.
The Defibtech Lifeline DCF-100 runs on a 9-volt lithium battery for self-checks. You can also use high-capacity lithium manganese dioxide packs for longer use.
- 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” models were huge and heavy, weighing about 250 pounds.
A Note About Manual Defibrillator Shock Energy…
Modern manual defibrillators, like automated ones, deliver biphasic shocks in joules. Clinicians can adjust the energy level on manual devices. In contrast, automated devices set it automatically.
Manual defibrillators allow precise control of shock intensity. This feature is helpful for infants needing lower energy levels. Only trained professionals, like doctors and paramedics, can operate them.
How Defibrillators Deliver an Electrical Shock
Automated defibrillation involves a basic three-step process.
Step 1: Cardiac Rhythm Analysis
Once the pads are on bare skin, the defibrillator checks the heart’s rhythm. It decides if a shock is needed. Don’t 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)
Some irregular heart rhythms can be fixed with a shock. Even when disorganized, the heart still produces electrical signals. The defibrillator briefly halts this chaotic activity, allowing a normal rhythm to resume.
Non-Shockable Rhythms
Not all cardiac rhythms respond to defibrillation. In asystole, there is no electrical activity. In pulseless electrical activity, signals look organized but don’t create a pulse. In these cases, a shock is ineffective because there is no disordered activity to reset.
Step 2: Shock Advised or Shock Not Advised
An AED first checks the heart’s rhythm. If a shock is needed, it uses battery power to charge up. This process, shown on the device, usually takes just a few seconds to reach the chosen energy level.
Once charged, the device either shocks on its own or tells the rescuer to press a button. This ensures no one touches the patient first. If the shock isn’t given quickly or the heart rhythm changes, the stored energy is safely released.
Step 3: Resume CPR
Once the shock is delivered, the AED signals it’s safe to resume contact. It tells rescuers to start CPR. Trained individuals should give compressions and breaths. Others can do hands-only compressions.
The AED checks the heart rhythm every two minutes. It decides if another shock is needed. Even if no shock is needed, keep the pads on. This lets the device monitor and respond if a treatable rhythm appears.
Importance of the Voltage of a Defibrillator for Lay Rescuers and AED Program Managers
Understanding voltage, current, and energy in defibrillation is vital for AED program managers and emergency responders.
- Do not touch the patient when the AED says “stand clear”! The body conducts electricity. So, touching the patient during analysis or shock delivery can disrupt treatment. It may also pass the shock to others, even through nearby metal objects.
- Remove medicated patches before placing the pads. Medicated adhesive patches, like nicotine patches, can disrupt electrical conduction. This increases the risk of burns because the device may deliver more energy. Removing them and cleaning the skin beforehand helps ensure proper pad contact.
- Don’t place the pads directly over a pacemaker or implantable cardioverter defibrillator. Implanted devices like pacemakers or ICDs can disrupt current flow. They may also get damaged by a shock. So, place pads a few inches away or adjust their position.
- Shave excessive chest hair. Excess chest hair can block pad contact. This increases resistance and limits current flow. So, it should be removed quickly to ensure a safe, effective shock.
Electricity, when properly delivered, can reverse common arrhythmias of cardiac arrest
An AED sends an electrical shock to stop dangerous heart rhythms. This shock is measured in volts, amperes, or joules. It can greatly boost survival rates during cardiac arrest.
Defibrillation alone isn’t always enough. Patients need advanced medical care too. Using an AED early, along with high-quality CPR, boosts the chances of survival and recovery after a cardiac arrest.
FAQs
What is the automated external defibrillator voltage?
Automated external defibrillator (AED) voltage is the electrical power an AED uses. This shock helps restore a normal heart rhythm during cardiac arrest.
How many volts are in AED devices?
Most AEDs generate thousands of volts internally. This helps deliver energy safely and effectively, though the exact voltage can vary.
What is the typical defibrillator voltage used during a Shock?
Defibrillator voltage varies by device and patient impedance. It’s carefully managed to ensure enough current reaches the heart.
Is AED voltage the same as energy in joules?
No, AED voltage is different from energy. Modern devices focus on joules (energy), while voltage is one part of how the shock is delivered.
Why is the voltage for a defibrillator important?
Voltage in the defibrillator is crucial. It helps push current through the heart. This is needed to stop dangerous rhythms so that normal activity can start again.
How does the AED voltage adjust during use?
The AED adjusts its voltage based on the patient’s body resistance. This ensures the shock is safe and effective.
Can defibrillator voltage be dangerous?
AEDs use high voltage for defibrillation, but they have safety systems. These systems ensure controlled shocks. This minimizes risk for both the patient and the rescuer.
Conclusion
Defibrillator voltage is key for restoring a normal heart rhythm during cardiac arrest. However, it’s one part of a controlled process. Current, energy, and patient impedance also play important roles. Modern automated external defibrillators adjust these factors on their own. This makes each shock safe and effective. Defibrillation is a life-saving tool, but it needs prompt and accurate use. Good CPR and advanced medical care also support its success.
