How much energy does a defibrillator deliver during a shock?

In case of cardiac arrest, quick defibrillation with a defibrillator is essential to restore the heart rhythm. But how much energy does a defibrillator actually deliver during an electrical shock? What voltage is used in a defibrillator? This is measured in joules (J) and varies by model and manufacturer. In this information page, we will explain how this 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 is normal for a defibrillator?

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 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 vulnerable:

• Special child electrodes, a child key, or a child button ensure that the defibrillator switches to child mode, automatically lowering the shock energy to 50 to 70 joules (depending on the defibrillator's 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 deliver a biphasic shock because it is more effective and causes less 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 aspect.  Defibrillators are designed to deliver an effective shock, regardless of the exact energy level. Manufacturers apply various technologies to ensure that the victim's body receives the right amount of energy.

At Medisol, we follow the motto: "All defibrillators save lives!" That’s why we are completely brand-independent.