Biphasic defibrillators have been commercially available for the past decade. With the increasing evidence of greater biphasic waveform efficacy,
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biphasic defibrillators are now established as the waveform of choice. Most manufacturers have now ceased monophasic defibrillator production and produce only defibrillators using a biphasic waveform. As a result, most hospitals are using a combination of older monophasic and newer biphasic defibrillators. Defibrillators used in hospitals are usually manual rather than automatic to enable greater flexibility in the delivered energy. The energy levels recommended for monophasic defibrillation are not necessarily appropriate for biphasic defibrillation, which is generally more efficacious at lower energy levels, particularly with ventricular arrhythmias of long duration.4
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We were concerned that there is currently considerable confusion as to how monophasic and biphasic defibrillators may be distinguished since the type of waveform is not usually immediately apparent on the defibrillator. From clinical experience, we also believed that there might be confusion as to the recommended energy levels for biphasic defibrillators.
One hundred and fifty anaesthetists of all grades from the Wessex region were surveyed to assess current knowledge regarding biphasic defibrillation. Each anaesthetist was asked to describe the difference between the two waveforms, how they would distinguish between a monophasic and biphasic defibrillator, and what would be an appropriate energy setting for the first shock in ventricular fibrillation using a biphasic defibrillator.
Fifty six percent (85/150) anaesthetists were able to describe the difference between the two waveforms correctly. The suggested method by which monophasic defibrillators could be distinguished from biphasic defibrillators is shown in Table 1. The first shock energy level for biphasic defibrillation of ventricular fibrillation is shown in Table 2.
Table 1Suggested methods as to how to distinguish between a monophasic and biphasic defibrillator
| Distinguishing feature | Number of anaesthetists (%) |
|---|---|
| Do not know | 50 (33.3) |
| It says on it | 84 (56.0) |
| You can just tell | 3 (2.0) |
| The energy settings are different | 7 (4.7) |
| You are told | 1 (0.1) |
| There is a label attached | 1 (0.1) |
| By the name of the machine | 2 (1.3) |
| They look different | 2 (1.3) |
Table 2First shock biphasic energy levels for defibrillation of ventricular fibrillation
| Energy level for first shock | Number of anaesthetists (%) |
|---|---|
| Do not know | 32 (21.3) |
| 100J | 13 (8.7) |
| 150J | 55 (36.7) |
| 200J | 11 (7.3) |
| Variable | 5 (3.3) |
| Depends on the machine | 16 (10.7) |
| Other | 18 (11.2) |
It can be clearly seen from this survey that there is a great deal of confusion relating to biphasic defibrillation, not only in terms of energy level administered, but also with regard to how to discriminate between the two types of machine. Where biphasic defibrillators are introduced into clinical practice, it is important that all relevant clinical staff undertake a comprehensive training scheme. As a result of this audit, we recommend that all defibrillators (both mono and biphasic) should also be clearly labelled with regard to their waveform and with appropriate energy settings for defibrillation.
References
- Efficacy of lower-energy biphasic shocks for transthoracic defibrillation: a follow-up clinical study.Prehosp Emerg Care. 2004; 8: 262-267
- Biphasic and monophasic shocks for transthoracic defibrillation: a meta analysis of randomised controlled trials.Resuscitation. 2003; 58: 9-16
- Transthoracic biphasic waveform defibrillation at very high and very low energies: a comparison with monophasic waveforms in an animal model of ventricular fibrillation.Resuscitation. 2002; 54: 183-186
- Patient outcomes following defibrillation with a low energy biphasic truncated exponential waveform in out-of-hospital cardiac arrest.Resuscitation. 2001; 49: 9-14
- Optimal Response to Cardiac Arrest study: defibrillation waveform effects.Resuscitation. 2001; 49: 233-243
- Multicenter, randomized, controlled trial of 150-J biphasic shocks compared with 200- to 360-J monophasic shocks in the resuscitation of out-of-hospital cardiac arrest victims.Circulation. 2000; 102: 1780-1787
- A comparison of biphasic and monophasic shocks for external defibrillation. Physio-Control Biphasic Investigators.Prehosp Emerg Care. 2000; 4: 305-313
- Monophasic versus biphasic transthoracic countershock after prolonged ventricular fibrillation in a swine model.J Am Coll Cardiol. 2000; 36: 932-938
- Increasing fibrillation duration enhances relative asymmetrical biphasic versus monophasic defibrillator waveform efficacy.Circ Res. 1990; 67: 376-384
Article info
Publication history
Received:
July 4,
2005
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© 2005 Elsevier Ireland Ltd. Published by Elsevier Inc. All rights reserved.
