chest compressions buy time by manually moving blood; brain death begins at minutes without flow
CPR actually works because it takes over the heart's job as a pump. When the heart stops, oxygenated blood is still sitting in the arteries and capillaries; a firm compression of the chest forces that blood toward the brain, and the release lets the heart refill for the next push. That cycle, repeated steadily, keeps the brain alive even though the heart itself is not beating.
The heart is a muscle that contracts to squeeze blood out. In cardiac arrest, it quivers or stops. Pressing on the lower half of the sternum squeezes the heart between the sternum and spine, raising pressure inside the chest and ejecting blood into the aorta. When you release, the chest recoils, pressure drops, and veins refill the heart. Full recoil is as important as the push, because if you lean, the heart cannot refill and the next compression pushes little.
At a rate of 100 to 120 per minute, the pause between pushes is about as long as the push itself. Suppose help takes 8 minutes to arrive with a defibrillator. At 110 compressions per minute, that is roughly 880 compressions. Each one gives the brain a small squirt of oxygenated blood. Not enough for normal function, but enough to slow the damage that begins after only a few minutes without blood flow.
CPR does not restart a stopped heart. It maintains a low level of circulation. The only treatments that can restart a shockable rhythm are a defibrillator for ventricular fibrillation or pulseless ventricular tachycardia, and sometimes medications given by paramedics. Rescue breathing is secondary; for an untrained bystander, uninterrupted compressions are recommended because stopping to breathe lets the blood pressure collapse and makes it much harder to restore good flow. The oxygen already carried in the blood is enough for several minutes, especially if the arrest was sudden and the person was breathing normally just before collapse.
CPR is far less useful when there is no blood to move. In severe bleeding or other forms of hypovolemia, compressing an almost empty heart does little, and the priority is stopping bleeding and restoring fluid volume. Likewise, if the arrest is caused by a tension pneumothorax or pericardial tamponade, the mechanical blockage must be relieved before compressions can have much effect. And for a drowning victim, the usual advice differs: rescue breaths may be more important early, because the oxygen remaining in the blood has been used up during the drowning process. Finally, if someone is unresponsive but breathing normally, compressions are unnecessary and can do harm; they are meant only for cardiac arrest.
The key point is that your hands act as a temporary pump, not a cure. Push hard and fast in the center of the chest, let it come back up fully, and keep going until help arrives. That is how the brain survives long enough for the defibrillator to do its real work.
Cram If someone collapses, I always thought CPR meant mouth to mouth rescue breathing first. Right?
Rep That is the old idea. The crucial part is chest compressions, because they keep blood moving to the brain.
Cram But if I am not breathing for them, how does the blood get oxygen?
Rep The blood still holds oxygen from the last breaths. Each compression pushes that oxygenated blood to the brain and heart.
Cram So my hands are basically doing the heart job?
Rep Exactly. Squeeze the center of the chest, pump the blood out, let it refill on the release. Every squeeze keeps the brain alive.
Cram How deep and how fast do I press?
Rep About five to six centimeters deep, at a hundred to a hundred twenty compressions per minute. Push hard and push fast.
Cram And if I get tired after a minute?
Rep That is why helpers should rotate. Studies show even a brief pause drops survival sharply, so keep the chest moving.
Cram Should I stop to give rescue breaths then?
Rep For untrained bystanders, hands only CPR is now recommended. Uninterrupted compressions beat loud breaks, and nobody hesitates to help.
Cram Because without blood flow the brain fails quickly.
Rep Yes. Brain cells begin to die within minutes without oxygen. CPR does not restart the heart, it buys time until a defibrillator arrives.
Cram So the real goal is keeping the brain alive until help gets there.
Rep Correct. Push hard, keep the blood moving, and let the machine deliver the shock. That is how a life is saved.