AED's are designed to shock both ventricular fibrillation and ventricular tachycardia without pulses. The key to this is that you must identify the patient to be unresponsive, because as stated above v-tach does occur with pulses and there is a vast difference in treating the two. Vtach with pulses (depending on the stability of the patient) can be treated with an anti arrhythmic medication such as amiodarone (my favorite) or in severe cases a strategically timed shock (which can only occur with advanced monitors (not aeds). The purpose behind CPR is to keep the patient viable. Studies show that survival rate declines by 10% for every minute someone is in cardiac arrest without CPR. That rate drops to less than 5% per minute (depending on the source) while CPR is in progress. The chaos and irritation in the heart will almost never resolve itself with CPR and this is why defibrillation is required.
ALL defibrillation including aeds must be done on a dry chest or dry area. When you stick those two pads on the chest the actually talk to each other and determine the amount of ohms of impedance the chest wall and organs have so the correct dose of electricity can be administered. No amount of science in the world is going to stop electricity from traveling through water so if you're standing in a soaking wet boat deck when you discharge that thing prepare to experience something new yourself.
When you have a hypothermic patient there are some many changes in the body, including a decrease in the metabolic rate that slows the process of death. These patients must be rewarmed while performing CPR and CPR cannot be stopped until they are warm and dead as the poster above me mentioned. There is alot that goes into the resuscitation of these patient from an advanced life support perspective but again CPR is the only thing that gives them a chance.
Just to clarify a point though, not all medics will transport patients to the hospital doing CPR. In the old days it was "load and go" you would race through the city swerving to get to the hospital so a doctor could pronounce them dead. Now studies have shown how ineffective CPR is while driving down the road, and the dangers it presents to everyone racing lights and sirens, coupled with the advances in prehospital medicine medics will often stay on scene and work someone until they achieve ROSC or the patient is pronounced. This does not apply to most cold water cardiac arrests however it was a side bar for anyone who may encounter and emergency and wonder why they aren't racing to the er.
And I know that for some reason my statistics are way above average. As a whole my department has consistantly been well above average nationwide for cardiac arrest ROSC. I attribute it to our training, the size and location of our stations/crews, our equipment and the fact our medical director is amazing at trying I stay cutting edge with our protocols.
---------- Post added March 23rd, 2013 at 12:46 AM ----------
Vincent, I'd love to try to elaborate on yor statement about if there is a defib problem CPR might not be effective, but I'm not entirely certain what you mean by defib problem?
