Journal of the New Zealand Medical Association, 07-May-2004, Vol 117 No 1193
Energy settings for mono- and biphasic defibrillation: guideline of the New Zealand Resuscitation Council
Duncan Galletly, Peter Larsen, Nigel Lever, Richard Aickin, and Warren Smith
The New Zealand Resuscitation Council (NZRC) has received many requests from health professionals in New Zealand to provide a clear guideline regarding the energy settings to be used for the defibrillation of ventricular fibrillation using biphasic devices.
On the basis of available evidence, the following rationale and recommendation were developed by the defibrillation advisory group of the NZRC, and were approved by the NZRC in September 2003.
For a person suffering a ventricular fibrillation arrest, the key determinant of survival is the time interval between collapse and the delivery of a defibrillating shock.1 International guidelines, emergency medical services, and (now) public access defibrillation programs are all based upon this evidence. To achieve successful defibrillation, sufficient electrical current needs to flow through the myocardium,2 but this need must be balanced by the caution that excessive current may cause direct injury to the myocardium.3
The shock output from defibrillators is measured as Joules of energy. Currently, the internationally agreed recommendation for monophasic waveform shock energies (in the treatment of ventricular fibrillation and unstable ventricular tachycardia) is an initial escalating triplet of shocks from 200, 200 (or 300), then 360 Joules, followed by further shock triplets maintained at 360 Joules.4 Although long experience has shown that this energy sequence is clinically effective1,4 there is no conclusive evidence to indicate that this sequence is indeed the optimal for maximising the number of victims who survive VF/VT arrest.5,6 The uncertainty in the optimal energy sequence is due primarily to a paucity of systematic research, which in turn is due (in part) to the significant ethical difficulties of resuscitation research.
In recent years, a range of defibrillators delivering biphasic shock waveforms have become available. Compared to monophasic waveform shocks, research clearly indicates that biphasic shocks achieve defibrillation rates equivalent to those of monophasic shocks, but at lower energies.6,7 A theoretical advantage of low-energy defibrillation is that it may result in less myocardial injury caused by the direct effects of the electrical current,8 but, in the clinically used range, the relevance of myocardial injury is not conclusively known.4
Biphasic waveforms vary in their shape according to the electronic method used in their production. The shape of the biphasic waveform used in a particular defibrillator differs according to manufacturer, and it is probable that the energy required for each biphasic waveform shape to be optimally effective differs according to that shape.9,10
Just as with monophasic waveforms, the ideal sequence of energy settings for biphasic defibrillators (used for a population of VF / unstable VT victims) is not presently known.4,6 Unfortunately, there are no dose-response studies to define optimal energy sequences based upon large-scale systematic study of human victims of ischaemia-induced ventricular fibrillation, and it is on the basis of less conclusive evidence that different energy sequences have been recommended by manufacturers for different devices delivering different biphasic waveforms.4,6
Although there are competing claims for particular biphasic waveforms and energy sequences, to date there is no conclusive evidence that any particular brand of biphasic device or waveform (or energy sequence), results in greater hospital-discharge rates of neurologically intact victims of human VF / unstable VT, than any other brand.4,6,11
Unfortunately, wide variations in manufacturer recommendations have the potential to create considerable confusion when a rescuer is faced with an unfamiliar defibrillator (of unknown waveform) during a cardiac emergency—and may create educational problems in attempting to provide a simply remembered guideline for recommended energy sequences.
Furthermore, although low (120–200 Joule) energy biphasic shocks appear to be more effective than high energy (200–360) monophasic shocks,4,6 it is not conclusively known whether high energy biphasic shocks are more effective than low energy biphasic shocks—and it is therefore impossible to state whether biphasic settings should optimally be lower than (or indeed similar to) the present monophasic settings.6
With the above considerations in mind, and because of the absence of conclusive human research evidence, the following recommendation is made by the NZRC. (We emphasise that the primary aim of this recommendation is to promote safe practice while further research evidence becomes available; it does not imply that higher shock energies are proven to be more effective).
The NZRC recommends that, for manual defibrillation, mono- and biphasic energy settings (for the treatment of VF / unstable VT in the adult), the initial settings should be 200, 200 Joules, followed by a third shock at the maximum available energy setting (up to a maximum of 360 Joules). All subsequent shocks should be given at the maximum available energy setting (up to a maximum of 360 Joules). If the rescuer is using a manual defibrillator that is not capable of delivering energies of 200 Joules, it is recommended that the maximum energy output be used throughout the resuscitation procedure.
In infants and children, it is recommended that monophasic and biphasic energy levels (using manually operated defibrillators) be given with initial escalating settings of 2, 2, and 4 Joules/Kg, followed by subsequent shocks at 4 Joules/Kg.
This NZRC recommendation provides:
The implications of this recommendation, for the major brands of defibrillator available in New Zealand, are shown in Table 1.
Table 1. Energy settings for three major brands of biphasic defibrillator available within New Zealand, used in accordance with the NZRC recommendation
Author information: Duncan Galletly; Peter Larsen; Nigel Lever; Richard Aickin; Warren Smith, NZRC Defibrillation Advisory Group, New Zealand Resuscitation Council, Wellington
Correspondence: Peter Larsen, NZRC Defibrillation Advisory Group, New Zealand Resuscitation Council, PO Box 7343, Wellington. Fax: (04) 389 5318; email: firstname.lastname@example.org
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