I was teaching class today, and I had a student tell me that an EMS system to our north was using a protocol that instructed rescuers to use two defibrilators simultaneously, in order to deliver 720 joules to patients in refractory Ventricular Fibrillation. At the time, I hadn’t known anything about this, so I told the student that this didn’t sound right, but that I would research the subject and get back to him.
It turns out that he was half correct. The procedure calls for two defibrillators to be used to deliver two shocks in rapid sequence, one with the traditional pad placement at the sternum and apex, and the other being in an anterior-posterior configuration. This is not delivering 720 joules, for the following reason:
Defibrillators do not deliver 360 joules per shock. Modern defibrillators are biphasic, and they deliver a shock that is EQUIVALENT to 360 monophasic joules. This means that when you press the shock button, the monitor measures the patient’s resistance to electrical current (called “impedance”), and delivers the energy that will get the appropriate energy to the fibrillating heart. This shock is actually 200j, and was determined to be the best energy level in clinical trials. (Mittal et al JACC 1999 24:1595-1601) Even so, the energy delivered would not even be equal to 400j, because the shocks are going to be delivered at least a half second apart. This makes them 2 “stacked shocks” of 200j each, not one 720j shock.
With that being said, systems using this procedure have had some success in converting stubborn Vfib with this protocol. My thought is that this is more due to either the placement of the pads of the second defibrillator in the anterior-posterior configuration, which would put more current directly through the heart, or is due to the fact that the shocks are being “stacked.” What strikes me as typical here is that there is serious talk about going back to “stacked shocks” as part of the ACLS algorithm, considering that the AHA removed those with the 2000 update. Will we see a return of them in the 2015 ACLS update?
Instead of recommending a return to stacked shocks, how about a study to determine is there is another factor at play here, like pad placement?