How much energy does a defibrillator deliver during a shock?

In case of cardiac arrest, quick defibrillation with a defibrillator is essential to restoring heart rhythm. But how much energy does a defibrillator actually deliver during an electrical shock? Wat voltage is used in a defibrillator? The energy is measured in joules (J) and varies by model and manufacturer. In this information page, we explain how it works!

What do joules mean in a defibrillator?

The energy delivered by a defibrillator during a shock is measured in joules (J). This is the amount of electrical energy sent through the victim's body to restore the heart to a normal rhythm. But how many joules does a typical defibrillator use?

According to adult resuscitation guidelines, the following applies (shock protocol):

• The first shock is delivered with 150 to 200 joules in a biphasic defibrillator (the most common technology)
• In a monophasic defibrillator (an older technology), the first shock must be 360 joules
• If the heart rhythm is still not restored after 2 minutes, the energy can be increased to a maximum of 360 joules.

For children, different guidelines apply as their bodies are smaller and more sensitive to electrical energy:

Special child electrodes, a child key, or a child mode button ensure the defibrillator automatically lowers the shock energy to 50 to 70 joules, depending on the brand and model.

Biphasic vs. Monophasic Defibrillation

There are two ways a defibrillator delivers a shock:

1. Monophasic: The electrical current flows in one direction through the body. This requires higher energy (360J) to be effective.
2. Biphasic: The current flows in two directions, meaning less energy (150-200J) is needed to achieve the same effect.

Almost all modern defibrillators use biphasic technology because it is more effective and reduces damage to the heart.

Is a higher number of joules better?

Many manufacturers emphasize the maximum number of joules their defibrillator can deliver, but in practice, this is not the most important factor. Defibrillators are designed to provide an effective shock, regardless of the exact energy level. Manufacturers use different technologies to ensure that the right amount of energy reaches the victim’s heart.

At Medisol, we follow the motto: "All defibrillators save lives!" That’s why we remain completely brand-independent, ensuring you find the right defibrillator for your needs.