Monday, September 08, 2008

The Almighty Defibrillator

And now, to change the subject just a wee bit...

I've run across some misinformation amongst some of my family members recently, regarding the use of defibrillators. Articles like this one from February indicate that they're not the only ones who may not understand. So what is a defibrillator, and what is it good for?
We'll start with the heart. It beats between 60-90 beats per minute (normally) in all of us who are alive to read this. The heart beats because inside the heart the "pacemaker", or sinoatrial node, generates an electric signal that courses through the heart muscle, which causes the muscles to contract, forcing blood up and out.

When the rhythm of the heart beat is normal, we call it "normal sinus rhythm". It looks like this:
Sometimes, the electrical system of the heart gets screwed up. It starts to fire in an abnormal fashion, causing the heart beat to become abnormal. We call this an arrhythmia. There are many types of arrhythmias. You can start with slow versus fast patterns. The thing to remember is there are MANY TYPES. Since there are many types of arrhythmias, it makes sense to think that patients have many types of reactions to their arrhythmias. Some patients with a benign arrhythmia may have no symptoms or may have severe symptoms. Some have a potentially lethal pattern and may have severe symptoms or no symptoms.

Now, what do you see on TV? Patient says "I can't breathe!", grasps their chest, and keels over; someone slaps the paddles together, yells "CLEAR!", then you hear BOOM! and the patient sits straight up, fit as a fiddle.

Not exactly.

In real life, the paddles only come out when a) the patient is sick enough and b) the rhythm is shockable. On airplanes and in school gyms, automated external defibrillators may be used instead of the big fancy paddles. Someone goes down, isn't breathing, and they look bad. Bystander grabs the AED, slaps on the pads, and the machine starts to analyze the patient. It has two options: shockable rhythm or non-shockable rhythm. That's it. The machine doesn't know if the patient is breathing, or conscious, or has no blood pressure; the machine simply knows whether it should deliver a strong shock or not.

So when will the machine deliver a strong shock? Two rhythms only: ventricular tachycardia and ventricular fibrillation. Both of these rhythms can be fatal, as the heart beats too fast to pump blood, so the brain dies, and the heart wears out, so it dies.

Unlike on TV, if someone's heart has stopped completely, or is in asystole, they don't get shocked. In that case, the only thing to do is good old-fashioned CPR: manual chest compressions and mouth-to-mouth (or bagging if you're in a hospital).

Thus, if you strap on an AED, it will not always shock the patient. It shouldn't. Pulseless electrical activity, where the heart has some electricity but isn't pumping blood to the body, does not respond well to shock. Asystole does not respond well to shock. The slow arrhythmias, unless they start having ventricular fibrillation, do not respond to this kind of shock (and require a special pacemaker). The correct thing to do, if the machine says "no shock advised", and the patient still isn't breathing, or has no pulse, is to continue CPR.

AED's can and do save lives--it's true. You can't go wrong by strapping one on someone who's down without a pulse and not breathing. But don't forget the CPR.

So, what was my family's misinformation? They thought that the machine always shocked--and therefore always saved. Not true. And unfortunately, if there's not a shockable rhythm, and the patient can't get help within minutes, their prognosis is grim, even with the world's greatest CPR (although with CPR is better than without). A patient who goes down may still have a poor prognosis even if the AED delivers a shock, but now they've got a fighting chance. Since you don't know why the patient is down--they may have had a heart attack, or a stroke, or a pulmonary embolus, or a chemical imbalance in their blood, any of which could trigger an arrhythmia--it's good to strap on the machine and do CPR.

Something random and (I think) fascinating: Hands-Only CPR can be just as effective as the regular kind. So, if you're worried about doing mouth-to-mouth, or don't have your barrier device handy, just work on the chest compressions (100 per minute, so faster than 1 per second, and compress the chest 1.5-2 inches in an adult).

--I'm going to use this for my family and other lay people who have questions about CPR and AED's. Let me know if there's something I should fix.

1 comment:

Rach said...

Great post! I'm teaching an aquatics course and I wish I had this about 6 weeks ago, because the 13 year olds looked at me like I had 6 heads and 14 eyes when i explained the AED... Next time around I may ask your permission to print this out and hand it out.

(oh and random comment moderation word for this comment? yafib - I kid you not)