The “Pre-Clear” & Other Tricks to Reduce the Perishock Pause

Push Hard. Push Fast. Don’t Stop.

By now, every single healthcare person out there should know that in order to improve a victim of cardiac arrest’s chances of meaningful survival, chest compressions are where it’s at. Blood needs to keep circulating in order to keep a person’s heart and brain alive and functioning. High quality chest compressions at a rate equal to or exceeding 100 per minute need to keep going without interruption, or at least without stopping for an exceptionally good reason such as defibrillation or to move yourself out of the way of an explosion or something similarly dangerous.

I’m reasonably sure that my entire audience already knows this and is doing all they can to keep high quality compressions going on every patient they attempt to resuscitate. It’s just good medicine and is really the only thing that’s ever been clearly shown to improve survival rates. Compressions = good. No compressions = bad. It’s pretty simple. Chances are that if you’re here reading an EMS blog you’re already well versed in this fact, but if you’re not, now you are. Keep pumping on those chests, ok?

As a paramedic who is keenly interested in the art of keeping his patients alive as long as possible, I am quite interested in new techniques and strategies I can use in order to stop interrupting the things that are doing the most good for my patients. Early on in my career, back when the medical system was more interested in the fancy tricks they had just taught me to use than they were with that boring BLS stuff, we used to pause compressions all the time. Even though we knew we should probably keep the patient’s heart, y’know, beating and all, we always seemed to put more time and emphasis into other things such as IV medications, endotracheal intubation, and even into moving patients into an ambulance and proceeding towards a hospital. Sure, we realized that we stopped compressions for a few moments here or there, but we weren’t really tracking just how much those moments were adding up. It turns out that those few seconds of paused compressions every so often were adding up to minutes and minutes of time when the patient’s blood wasn’t going where it needed to go. We were wrong to do that and I’m glad that now we’re acutely aware that no matter what, we need to keep that blood moving.

I am still somewhat convinced that ALS treatments like medications and airway management are necessary, especially for the moments before a patient arrests where we can stop the code before it starts and after the resuscitation where we can keep the heart beating effectively. However I absolutely cannot condone moving patients in cardiac arrest without a compelling reason related to provider safety or patient rescue. Patients in cardiac arrest need to be worked where they are found, or at least as close to it as possible in an area with enough room to effectively operate. There is no reason to take a patient to a hospital when they are in cardiac arrest. There is no reason to put them in your ambulance unless you are in danger or if they were already in there when their heart stopped. Transport reduces the effectiveness of compressions. So does moving a patient. Just don’t do it. Your ALS equipped ambulance should be more than adequate to save the ones that can be saved. If it isn’t, your protocols need changing. There is no magic pixie dust at a hospital that cannot be carried in an ambulance. At least no pixie dust worth bringing most of your patients’ overall chances for survival down to nothing for. BLS crews in rural areas should start and continue resuscitation while ALS is on the way to the scene.

Implementing strategies that help keep compressions going without pause is a key component in performing well during resuscitation attempts. I enjoy learning about and implementing them and you should too. One of them I learned a few years back, for instance, was to start getting immediately “back on the chest” after a defibrillation attempt instead of groping around in an attempt to see if a pulse came back. The heart needs to be pumping blood via chest compressions the instant after a shock is given. This improves survival rates and does not hurt a beating heart should the defibrillation attempt succeed. Don’t even worry about checking for a pulse or looking at the monitor after you shock. Just keep pumping. Another, more recent technique is to pre-charge the defibrillator before briefly pausing compressions to simultaneously switch compressors, look at the rhythm, give a shock if needed, and then get right back on the chest. This eliminates those few seconds it takes for the defibrillator to charge up its capacitors with the required energy level (that annoying “BoooooOOOOOOOO” noise it makes) before a shock can be delivered. When we started that practice, the looks we got from the people doing compressions were pretty alarming but they’ve gotten used to it by now and we haven’t inadvertently shocked anybody yet, so yay science!

Speaking of the above, there is a term for those moments of time between the instant we stop compressions and the time that a defibrillation shock is administered. It’s called the “Perishock pause” and it’s too long. Shortening that pause is another way we can squeeze more life into more people.

A post by Tom Bouthillet whom you probably know from the excellent blog helped me think of this. He posted a study on his Facebook Page that started me thinking about how we could implement a new strategy to help. The study looked at the effects of the perishock pause on survival rates and found something that we all pretty much could have guessed if we had chosen to think about it:

“In patients with cardiac arrest presenting in a shockable rhythm, longer perishock and preshock pauses were independently associated with a decrease in survival to hospital discharge. The impact of preshock pause on survival suggests that refinement of automatic defibrillator software and paramedic education to minimize preshock pause delays may have a significant impact on survival.” (1)

Another article regarding the same study phrased the results this way:

“Conclusions: Peri-shock pause was an independent predictor of survival to discharge in this cardiac arrest registry.” (2)

If you take the time to read the study, you’ll see that the impact on survival caused by shortening or eliminating the perishock pause is impressive and important. It’s another one of those little things we might not have thought of that is impacting survival rates. It needs to be eliminated.

I’ve got two strategies to help with this, the first being something that isn’t my idea but that is an idea I fully support. I believe that AEDs should be relegated solely to public access programs and first responders and that EMS personnel of all levels should be using manual defibrillators. It’s not hard to recognize V-fib and the time it takes for an AED to analyze, charge, and deliver a shock is unacceptably long when compared to the ease of training EMTs and AEMTs to recognize V-Fib on a monitor screen and shock at maximum energy. There’s simply too little risk and too much benefit to keep a manual defibrillator solely in the hands of ALS personnel.

The other is what I call, “The Pre-Clear”

The Pre-Clear is a practice where everyone but the person actively providing chest compressions clears the patient in anticipation of delivering a defibrillation shock. The code commander calls out “Pre-Clear!” before he or she charges the defibrillator about ten seconds before the two-minute interval hits. Once it’s fully charged, the code commander calls “Clear,” visually confirms the compressor is clear, verifies the rhythm, shocks, and calls “back on the chest” in under 5-10 seconds. This effectively slashes the time it takes for the current practice of stating “I’m clear. You’re clear. Everybody’s clear” which the authors of the above study determined could take up to 20 seconds or longer. Those seconds really add up and they are proven to be harming our patients. Any strategy that shaves those extra seconds off really seems to make a difference.

I think the “Pre-Clear” method might be an effective way to reduce the perishock pause and I will be working it into my future resuscitations. It can’t hurt and might just help us push our survival rates even higher. Learn about how you perform during resuscitations and practice with your team. Be a good leader, a good follower, and an exceptionally competent provider. Little things matter. Pay attention to them for the good of your patients.


"Pre-Clear" + charge + "Clear" + Shock >10sec

“Pre-Clear” + charge + “Clear” + Shock >10sec



  1. Perishock pause: an independent predictor of survival from out-of-hospital shockable cardiac arrest. – Cheskes S1, Schmicker RH, et al. Circulation. 2011 Jul 5;124(1):58-66.
  2. Abstract 266: Peri-Shock Pause: an Independent Predictor of Survival From Out-of-Hospital Shockable Cardiac Arrest – Presentation, Resuscitation Science Symposium


  1. How the Peri-Shock Pause in Automated External Defibrillators Affects CPR – Christopher Watford, BSc, NREMT-P | David Baumrind, BA, EMT-CC  – JEMS, February 2013
  2. Perishock Pause – EMRAP Podcast – May 2013
  • Christopher

    A trick we use at our service is to designate somebody to count down once the “hold compressions” command is given. They count down aloud from 5 (5..4..3..2..1..GO), letting the interpreter/button masher know that they’d better get a move on. The next compressor watches for the button push or the GO from the countdown role.

    If the button masher can’t determine if the rhythm is shockable in 5 seconds…the rhythm is not shockable.

    Some folks were worried about the next compressor getting shocked if they moved when the button was pushed…so you can let them know that their human reaction time is longer than the shock delivery time. The defibrillator could throw in 5 shocks in the time it takes you to even realize the button is being pushed!

    • Barefoot in MN

      this is related to why when I’m doing compressions, I count out loud, & about the 20 mark I ask the person doing respirations to get into position. (I know, they ought to be already.) What I’d like is a partner who anticipates. Those seconds & fractions thereof do add up.

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  • sean

    Well done. Btw, thumper have been shown to consistently deliver better compressions with little to no interruptions.
    The next thing we need to tackle is when we “call it.” I saw a 60 minutes episode where the wife of an icu nurse went down and he did cpr on her for an hour before she came back…and with nominal neuro deficits.

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