Defibrillation involves delivering a controlled electrical shock to the chest to reset the heart’s chaotic electrical activity, such as ventricular fibrillation, back to a normal rhythm. The energy used for this procedure is measured in Joules (J), which represents the amount of electrical work delivered. The exact number of Joules required for a successful shock is not a single, fixed value, but depends heavily on the type of technology used in the defibrillator device. The appropriate dose also varies significantly depending on the patient’s age and body weight.
The Critical Difference Between Biphasic and Monophasic Defibrillation
The fundamental reason for the wide range of energy settings is the difference between monophasic and biphasic electrical waveforms. Monophasic defibrillators, which represent older technology, deliver the electrical current in a single, unidirectional pulse. To achieve successful defibrillation, this technology requires a high energy input, typically set at 360 Joules for all adult shocks.
Biphasic technology, which is the modern standard, delivers the current in two phases, reversing the direction of the electrical flow halfway through the pulse. This approach is significantly more efficient, allowing biphasic devices to terminate ventricular fibrillation using substantially lower energy levels than monophasic counterparts. They also reduce the risk of post-shock complications, such as damage to the heart muscle and skin burns, because less overall energy is applied. Modern biphasic devices have largely replaced monophasic units.
Standard Energy Settings for Adult Defibrillation
For adult patients experiencing ventricular fibrillation or pulseless ventricular tachycardia, the standard energy dose depends on the specific device. Manual biphasic defibrillators, typically used by advanced medical providers, usually recommend an initial shock in the range of 120 to 200 Joules. The exact starting dose within this range is specific to the manufacturer and the device’s unique waveform design, such as rectilinear or truncated exponential biphasic.
If the first shock is unsuccessful, guidelines suggest that subsequent shocks should be delivered at the same dose or at an escalating dose, depending on the device’s capabilities. If the rescuer is unsure of the manufacturer’s recommended setting, the highest available energy dose on the device is often advised for the initial shock. Monophasic devices, if still in use, deliver a fixed dose of 360 Joules for every adult shock attempt.
Automated External Defibrillators (AEDs), designed for public use, are universally biphasic but function differently. These devices are pre-set by the manufacturer to deliver their maximum effective dose, typically between 150 and 200 Joules. The user does not manually select the energy level; the device automatically charges and delivers the fixed dose upon analysis of a shockable rhythm. A standard biphasic AED is recommended for any adult patient, delivering the appropriate low-energy shock with high success rates.
Adjusting Defibrillation Energy for Pediatric Patients
Defibrillation for infants and children requires a significantly different approach, as the energy dose must be carefully calculated based on the patient’s body weight. This is in stark contrast to the standard fixed-dose approach used for adults. The initial energy dose recommended for a pediatric patient is 2 Joules per kilogram (J/kg) of body weight.
This lower weight-based dose is necessary because a child’s smaller body size and cardiac mass could be damaged by the high energy levels used for adults. If the initial 2 J/kg shock is unsuccessful, subsequent shocks are typically escalated to a higher dose, usually 4 J/kg. Higher energy levels, up to a maximum of 10 J/kg, may be considered if subsequent shocks continue to fail.
When using an AED on a child between one and eight years old, special pediatric pads or cables are necessary. These pads contain an energy attenuator that reduces the standard adult energy dose to the lower, weight-appropriate level for the child. For children under one year of age, a manual defibrillator is generally preferred to ensure accurate, weight-based energy delivery.