Semi-automatic shocks make long delays in CPR

By Eleanor McDermid, Senior medwireNews Reporter

Paramedics should avoid using defibrillators in semi-automatic mode, say researchers who found this increases interruptions to cardiopulmonary resuscitation (CPR) in the 30 seconds preceding shock delivery.

Using defibrillators in semi-automatic rather than manual mode did not affect the success rate of the shock, but did significantly reduce the prehospital rate of return of spontaneous circulation (ROSC), the prospective study findings show.

Study author Andrew Swain (University of Otago, Wellington, New Zealand) and team caution that a larger study would be required to look at survival to discharge. Their study only included 44 patients, because it was stopped early for ethical reasons raised by the increased rate of ROSC with use of manual mode.

The prehospital ROSC rate was 18.49% after 119 manual shocks, compared with 8.33% after 84 shocks in semi-automatic mode.

Semi-automatic mode "is often preferred, even by senior paramedics, as it allows other resuscitation needs (such as immediate chest compressions, ventilation, equipment preparation and cannulation) to be addressed simultaneously," write the researchers in Resuscitation.

But they say that their findings "have prompted changes to local prehospital defibrillation protocols and teaching to emphasise that manual defibrillation is the preferred mode amongst appropriately trained paramedics."

Use of manual mode reduced pre-shock pauses by a small but significant 1 second, at a median of 3 versus 4 seconds in semi-automatic mode. The corresponding cumulative interruption to CRP during the 30 seconds preceding shock delivery amounted to 7 versus 14 seconds.

The post-shock pause did not differ with the defibrillation mode used, and the success of shock delivery was similar, at 75.6% and 70.2% for manual and semi-automatic mode, respectively.

Swain et al say that their findings confirm those from registry analyses. They note that increased pre-shock pauses in semi-automatic mode are thought to arise from voice prompts, while interruptions during the 30 seconds before shock delivery are likely caused by the hands-off rhythm-analysis period. In manual mode, rhythm analysis is normally part of the pre-shock pause, reducing the overall interruption of CPR.

"We attribute our higher rates of ROSC in manual mode to shorter CPR pauses in both the pre-shock phase and the 30 [seconds] preceding shock delivery," say the researchers.

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