To learn and remember CPR, it helps to understand the physiology behind it. To help, we're going to take a trip back to your High School Biology class to explain how CPR works.
Let’s start with the heart. Where do you put your hand when you say the “Pledge” each morning before work? Well, if you feel a heartbeat there, it’s probably your Aorta. Your heart actually lies in the middle of the chest, beneath the sternum, or breastbone. When we compress the chest during CPR, the rescuer places the heels of his/her hands on the sternum and presses downward with enough force to compress the heart.
Properly performed compressions will squeeze the heart between the sternum and the spine, forcing blood away from the heart. Releasing pressure will allow the heart to refill with blood. Repetitions of this activity will simulate the heart’s natural beat, and will pump the blood through the body where it is needed.
Well, that’s half of it. You must remember that merely moving the blood through the body is not enough to keep the brain alive for long. Blood is just a carrier, and what it needs to carry is Oxygen. Oxygenated blood is easy to recognize because it is bright red, while deoxygenated blood is blue. When an individual’s skin becomes blue it means he or she may have plenty of blood, but they have run out of oxygen.
There are two major types of blood vessels that we will discuss; they are Arteries and Veins. Arteries are the larger ones. Arteries carry bright red blood. Arteries travel AWAY from the heart. If you can find a pulse on your body, it’s an artery. If you cut an artery, it won’t be something you’re likely to forget; arterial bleeding is characterized by forceful spurts of blood that leave the body rapidly. When the red, arterial blood reaches the extremities, the oxygen is released and the blood turns blue. This blue blood will return to the heart through a system of Veins. Veins are the opposite of arteries. Veins carry blue, deoxygenated blood back to the heart, and ultimately to the lungs, to get more oxygen.
The heart has four chambers. The upper chambers (Atria) are the “receiving” chambers, while the lower, more heavily muscled chambers (Ventricles), are responsible for “pumping.” When the veins bring the blue blood back to the heart, it arrives in the right atrium, is sent down to the right ventricle, and the ventricle pumps the blood off to get oxygen in the Lungs. We tend to think of our lungs as a couple of big air sacs, but there are actually thousands of tiny air sacs called Alveoli that trap the air as it enters the lungs. The air that we breathe contains about 20.8% oxygen that is immediately absorbed by the blood that surrounds these alveoli. When the blood and the oxygen have combined, it turns bright red, returns to the left atrium of the heart, passes into the left ventricle, and ultimately is pumped out to the body through the Aorta.
There are a few arteries that should be identified before we continue. The first is the Aorta. It is the biggest artery in the body, leaving the heart from the left ventricle. Sometimes, an individual experiencing a heart attack will describe pain radiating toward their left arm, following the path of the Aorta. The first major artery to branch off of the Aorta is called the Coronary Artery. The Coronary arteries circle back to provide oxygenated blood to the heart. The heart needs oxygen like any other organ, and the Coronary arteries make this possible. I mentioned earlier that brain cells live for only 4-6 minutes in the absence of oxygen. Well, heart tissue is made of specialized cells that will die almost immediately when the oxygen supply is cut off. If you’ve ever heard of someone having a “Massive Coronary,” it means that a lifeline to his or her heart has been blocked. An occluded Coronary Artery means a heart attack, or cardiac arrest is imminent.
Another important set of arteries is the Carotid. These lead up the sides of your neck, providing the major blood pressure to your brain. You may be able to locate them by placing your first two fingers on the side of the neck, just below the curve of the jaw. Current Emergency Cardiovascular Care (ECC) 2001 guidelines suggest responders are now to “look, listen & feel” for signs of circulation, which include normal breathing, coughing, movement, and/or a pulse. Some helpful hints for finding a pulse:
- You have two Carotid arteries. If you don’t feel it on one side, try the other, but don’t try both sides at the same time. That’s called strangulation.
- Resist the urge to check for pulses with your thumb. The thumb often carries its own pulse, which can give you the false impression that a coffee table is going to be “just fine.”
One more artery before we wrap up our Biology flashback. This one’s called the Brachial. It runs along the Humerus, between the underarm and the elbow, and between the bicep and the tricep. This artery is useful when Medical personal are checking the pulse of an infant. They don’t check the Carotid artery on babies because their necks are covered in baby fat. Okay, I’ve shown you this interaction between the heart and lungs to reiterate a point made earlier in this class. Breathing and heartbeat are what CPR is all about. Heart and lungs. Later on I’ll attempt to confuse you with all kinds of numbers, ratios, rates, depths of compression and so on. But if you forget all of this, remember the basics: If they’re not breathing, breathe for them. And if there’s no pulse, beat their heart. That’s the essence of CPR.