You've just finished renewing your CPR card at the firehouse, and now you're sitting in the day room with your classmates. One of them is frustrated that the guidelines keep changing. "First it's five compressions to one breath," he says. "Then it's 15 to two, and now 30 to two. And what about shocking first? They just can't seem to make up their minds." You liked the class, but you can't help thinking about all the cardiac arrests you've been on over the years. For all the changes in CPR and the new toys and drugs paramedics use now, very few patients seem to get pulses back and walk out of the hospital. You wonder if things will change with the new guidelines.
Despite advances in care over the years, survival from out-of-hospital cardiac arrest remains low, averaging about 6% worldwide.1 It's easy to get cynical about all the changes recommended by the American Heart Association (AHA) and wonder if the latest ones will make any difference. However, there are several things that make this revision of the AHA's Basic Life Support (BLS) and Advanced Cardiac Life Support (ACLS) guidelines different.
First, the science behind cardiac arrests is more robust and the pathophysiology is better understood now. An international committee of experts met and closely scrutinized studies of cardiac arrests to see what works, what might work and what doesn't.1 Second, there is new insight into what happens to patients in cardiac arrest, which helps determine what treatment options are most likely to work.2
Looking at what has worked in the past and understanding what's happening to the body during cardiac arrest, it is clear that EMS must rethink its approach to managing these cases. The key is to prioritize our interventions and perfect the ones that are most important.
THE THREE PHASES OF CARDIAC ARRESTS
The vast majority of sudden cardiac arrests begin with ventricular fibrillation (v-fib), where electrical impulses chaotically fire from all parts of the heart instead of the normal pathways. This causes the heart to "quiver," and no blood can be pumped from it. An AED will deliver a shock if this rhythm (Figure 1) is detected. The heart may also have electrical activity conducted through normal pathways and appear normal on a monitor when it's really not pumping in response to the electrical impulses. This is known as pulseless electrical activity, or PEA (Figure 2). Finally, there may be no electrical activity in the heart at all, and subsequently no pumping. This is known as asystole, and appears as a flat line on a monitor.
Previous cardiac arrest treatment guidelines focused only on the rhythm displayed. Upon detection of v-fib, shocks were delivered immediately. Now it appears that simply defibrillating anytime v-fib is seen may be not be helpful. A three-phase model of the body's changes during cardiac arrest has been proposed, and the appropriate treatment now depends on the patient's time of collapse or which phase they're in.2
I. Electrical phase (0–5 minutes)—For the first five minutes of a cardiac arrest with v-fib, the best treatment is immediate defibrillation. Because the patient's time down usually isn't known, the only patients who should be defibrillated immediately are those whose arrests were witnessed by EMS.2,3
II. Circulatory phase (5–10 minutes)—If a patient has been in v-fib longer than five minutes, defibrillation is more likely to be successful after a period of CPR. Defibrillating without doing CPR first is more likely to convert the rhythm to asystole or PEA, making the chances of survival even smaller. For most patients in arrest on EMS arrival, it is safe to assume that more than five minutes have passed since collapse.2,3