Cardiac arrest, let's talk about defibrillator voltage

By Cristiano Antonino Last updated Jun 20, 2023

The defibrillator is a device capable of generating a controlled electrical discharge to the heart in order to re-establish the rhythm of its beats in the event of cardiac arrest or rhythm alterations

It is used in the medical field and is capable of interrupting an arrhythmia using direct current that supplies it with a low voltage, which is capable of reaching up to 220 volts from about 15 thanks to a transformer with a mains power supply.

Typically, the defibrillator is powered by a rechargeable battery, mains or 12-volt direct current; it consists of two electrodes that are placed to the right and left of the patient’s chest, while the ‘core’ analyses the data transmitted to it.

Before moving on to quantify voltage and discharge energy, let us briefly touch on function and structure.

Defibrillator: types and operation

The manual defibrillator has two electrodes that deliver the discharge to the patient’s chest; frequency modulation is the responder’s responsibility.

The semi-automatic defibrillator works in semi-automatic mode by electrocardiogramming the victim in order to check whether intervention is necessary or not.

The automatic defibrillator is connected to the patient and will automatically deliver the shock if the victim has suffered cardiac arrest.

Another type of defibrillator is the internal defibrillator, a small battery-powered stimulator; thanks to its small size, it can be implanted in the heart muscle, and its function is to record any abnormalities by intervening when needed.

Defibrillator circuits

Defibrillators are made up of two types of circuit; a low-voltage circuit and a high-voltage circuit.

The first, of 10-16 V, powers all the functions, from the monitors to the microprocessors; the second, concerns the mechanism for charging and discharging the defibrillation energy, which can be up to 5000 V.

These devices are equipped with an internal resistor; in automatic or manual mode, depending on the type of defibrillator, the energy stored by the capacitor is discharged.

To transmit the shock to the patient, the discharge button is pressed, the electrode-monitor circuit is closed, and the electrocardiogram trace is taken.

Defibrillator Voltage and Energy

The defibrillator, powered by a rechargeable battery, has a voltage that varies from 10 to 16 volts if the circuit is low voltage up to 5000 volts of defibrillation energy; the discharge energy is usually 150, 200 or 360 J.

In the adult, the required discharge energy is about 200 J at the first delivery, and up to 300 J at the second.

With the use of the same amount of energy, higher current levels are achieved one shock after the other, the increase in transmitted current occurs with a higher amount of energy delivery.

If the first two shocks are not effective for defibrillation, the third shock will have to increase its energy to 360 J.

The constant application of energy will accumulate in the capacitor, the current delivered is related to the resistance or impedance between the defibrillator electrodes.

Impedance, is the resistance to the flow of electrons, measured in Ohms, while the pressure pushing the same electrons is called electrical potential, this is measured in Volts.

Defibrillation allows a flow of electrons to pass through the heart for a short unit of time, thus generating current, which is measured in amperes.

We therefore have electrons passing for a few milliseconds through the heart by means of a substance that generates resistance under a certain pressure.

The risks that can be generated when using the defibrillator concern the high impedance that leads to reduced effectiveness, generating sparks between the electrodes and increasing the danger of burns.

This is more likely to occur especially in patients in whom there is little electrical contact due to hairiness, which facilitates the formation of air between skin and electrodes; to avoid burns, it is also necessary to ensure that the electrodes do not touch each other, touch bandages, transdermal patches, etc.

It is essential to observe safety regulations in order to ensure that the defibrillator voltage is not hazardous to the victim’s health.

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