For treatment of ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT), the 2005 Guidelines recommend one shock followed immediately by 5 cycles (about 2 minutes) of CPR prior to re-analysis of the patient ECG rhythm. This replaces the series of up to 3 shocks followed by the pulse check or check for signs of circulation prior to the initiation of CPR. This recommendation applies to all rescuers including lay providers.

This major change is based on the high first shock success rate of new defibrillators with biphasic waveforms and the clinical evidence that if the first shock fails, chest compressions may improve oxygen delivery to the myocardium, making the subsequent shock more likely to result in defibrillation. The pulse check or check for signs of circulation step uses valuable time and rescuers often cannot reliably perform it. This time could be better spent performing CPR. Implementation of this protocol change will require modifications to most AEDs on the market.

This is a key feature of the new cprMAX™ technology to be implemented in Physio-Control defibrillators. Appropriate voice prompts along with elimination of stacked shocks will guide rescuers to perform chest compressions and rhythm analysis appropriately.

Shock success becomes all the more important with the new protocols calling for 2 minutes of CPR between defibrillation shocks. Not all brands of biphasic AEDs have demonstrated high first shock success for long duration VF. To order a reprint of an article evaluating the shock success of the ADAPTIV biphasic waveform as compared to a monophasic waveform, contact Physio-Control Sales. You will be routed to our request page; please type "van Alem Study" in the message box that appears. [1]

EMS medical directors may implement a protocol providing about 5 cycles (or about 2 minutes) of CPR before defibrillation for unwitnessed arrest, particularly when the interval from the call to the EMS dispatcher to response at the scene is more than 4 to 5 minutes.

This is a major change, though optional. Many EMS systems have implemented this protocol already. There is clinical evidence supporting CPR prior to defibrillation for unwitnessed arrests, when response times are longer than 4-5 minutes from call to arrival on scene. cprMAX technology will allow EMS systems to adopt this protocol without "fighting the prompts."

There is insufficient evidence to support or refute CPR before defibrillation for in-hospital cardiac arrest.

In the hospital it is acceptable to deliver one shock followed by immediate compressions. In specific settings such as monitored areas, this sequence may be modified at physician's discretion.

With monophasic defibrillators the initial and subsequent defibrillation energy should be 360 J.

"If the monophasic AED being used is programmed to deliver a different first or subsequent dose, that dose is acceptable."

For facilities with monophasic devices, the new monophasic dosage recommendation will require retraining. This may be an opportune time to switch completely to LIFEPAK defibrillator/monitors with ADAPTIV biphasic technology, which follow the same 200J-300J-360J dosage protocol familiar to responders using monophasic devices prior to Guidelines 2005.

Recommended first shock biphasic energies

Truncated exponential: 150 J - 200 J.

Rectilinear: 120 J.

Subsequent doses should be the same or higher.

"When transthoracic impedance is too high, a low energy shock will not generate sufficient current to achieve defibrillation."

Download a view of the available dosage ranges for the leading defibrillator/monitors (PDF, 444 kb).

New clinical data on the benefit of escalating energy (i.e. subsequent doses at higher energy) have emerged since the scientific review upon which the Guidelines energy recommendations are based. Download a view of the data (PDF, 586 kb). To order a reprint of this abstract, contact Physio-Control Sales. You will be routed to our request page; please type "Chapman abstract" in the message box that appears.

"With the rectilinear biphasic waveform device, selected and delivered energies usually differ; delivered energy is typically higher in the usual range of impedance. For example, in a patient with 80 O of impedance, a selected energy of 120 J will deliver 150 J."

This comment addresses the difference between set and delivered energy that is characteristic of one company's AED with rectilinear biphasic technology. This difference adds to the confusion that customers face when evaluating the wide variety of AEDs and unique waveforms on the market. One good measure of waveform effectiveness is shock success in a real-life setting. Shock success becomes all the more important with the new protocols calling for 2 minutes of CPR in between defibrillation shocks. Not all brands of biphasic AEDs have demonstrated high first shock success for long duration VF. To Order a reprint of an article that evaluated the shock success of the ADAPTIV™ biphasic waveform as compared to a monophasic waveform, contact Physio-Control Sales. You will be routed to our request page; please type "van Alem Study" in the message box that appears. [1]

Regarding VF out-of-hospital sudden cardiac arrest: "No direct comparison of the different biphasic waveforms has been made."

"None of the available evidence has shown superiority for either nonescalating or escalating energy biphasic waveform defibrillation for termination of VF. Nonescalating and escalating energy biphasic waveform shocks can be used safely and effectively to terminate short-term duration and long-duration VF. (Class IIa). The safety and efficacy data related to specific biphasic waveforms, the most effective initial shock, and whether to use escalating sequences require additional studies in both the in-hospital and out-of-hospital settings."

A randomized out-of-hospital comparison of escalating vs. fixed dosage was recently published showing a significantly higher rate of VF termination when an escalating dosage protocol is used. Download a slide summarizing the data (PDF, 571 kb). Read a discussion of this study provided by Physio-Control (PDF, 92 kb). To order a reprint of this article, contact Physio-Control Sales. You will be routed to our request page; please type "Walsh Study" in the message box that appears.

"Manufacturers should display the device-specific effective waveform dose range on the face of the device, and providers should use that dose range when attempting defibrillation with that device." (p. IV-40) "Providers should be aware of energy levels at which their specific waveform was shown to be effective at terminating VF." (p. IV-40) "If a provider is operating a manual biphasic defibrillator and is unaware of the effective dose range for that device to terminate VF, the rescuer may use a selected dose of 200J for the first shock and an equal of higher dose for the second and subsequent shocks."

This particular recommendation applies to manual defibrillators.

Download a position statement on Physio-Control's recommended biphasic dosage protocol (PDF, 44 kb).