To the Editor: With the increasing availability of biphasic defibrillators for use in both the manual and shock-advisory modes, considerable confusion has developed as to the appropriate energy levels to be used with these devices. This confusion has arisen partly because of differing recommendations from manufacturers, partly as a result of limited clinical evidence and partly because of the clinical availability of both monophasic and biphasic defibrillators. The differences between these waveforms are the way energy is delivered. Biphasic energy is delivered in two directions, whereas monophasic energies are delivered in one direction.

Recommendations of the International Liaison Committee on Resuscitation state that biphasic energies less than or equal to 200 J are as efficacious as escalating higher-energy monophasic shocks.1 Lower-energy biphasic shocks cause less myocardial injury and postresuscitation myocardial dysfunction, and so potentially improve the likelihood of survival.2 Faced with the lack of data with respect to biphasic energy levels, the Australian Resuscitation Council makes the following recommendations:

1. When using manual biphasic defibrillators, energy levels of 150 J should be used for defibrillating ventricular fibrillation and pulseless ventricular tachycardia in adults.

The basis of this recommendation is as follows: one randomised controlled trial in people in out-of-hospital ventricular fibrillation compared monophasic and biphasic shocks delivered by automated external defibrillators (AEDs).3,4 This study showed that 150 J biphasic shocks achieved higher rates of defibrillation and return of spontaneous circulation than higher-energy (200 J/200 J/360 J) escalating monophasic shocks. No differences were observed in the proportion of patients discharged from hospital.

As clinical superiority of one particular biphasic waveform over another has yet to be demonstrated, it is appropriate to recommend this single energy level to achieve a consistent approach.

2. Biphasic energy levels of 1–2 J/kg should be used for defibrillating ventricular fibrillation and pulseless ventricular tachycardia in children.

The basis of this recommendation is as follows: extrapolation from adult data, supported by studies in “child” and “infant” animal models, suggests that the dose for biphasic shocks in children should be 1–2 J/kg (about half the monophasic dose). Higher doses (up to 4 J/kg) are not likely to be harmful and are more efficacious than equivalent monophasic shocks.5 Biphasic shocks may be delivered in a fixed dose of 50 J by an AED.

The use of AEDs in children less than 1 year of age is not recommended, as in this situation these devices are unable to differentiate between shock-able and non-shockable rhythms (eg, ventricular fibrillation v pulseless electrical activity).

Energy levels for AEDs when used in automatic mode have been pre-set by the manufacturer, and do not require an energy level to be set by the user.