Q: How long does it take for someone to die if their carotid artery is compressed?
A: The two carotid arteries lie in the front of the neck on either side of the trachea (windpipe) and carry blood from the heart to the brain. They supply 90% or so of the brain’s blood, with the rest coming from the two small vertebral arteries that travel along the spine and over the back-most portion of the brain. The carotids are interconnected in the brain so that in a normal individual compressing a single carotid artery will have little effect. Compressing both can cause a loss of consciousness in 15 to 20 seconds and death in 2 to 4 minutes.
One general rule in medicine is that if the heart stops, the victim will lose consciousness in about 4 seconds if standing, 8 if sitting, and 12 if lying down. This simply reflects the effects of gravity on blood flow. These numbers would also mostly hold true if both carotids were suddenly pressed shut—not easy to do—see below. But, to the brain, the complete interruption of blood flow through carotids would look the same as it would if the heart had stopped. Either way, the brain would receive no blood supply, and the brain needs a continuous supply of blood to function and survive.
Another medical truism is that dizziness, loss of consciousness, and sudden death are simply gradations along the same scale. That is, what makes you dizzy can make you lose consciousness, and what makes you lose consciousness can cause death. One of the things that can do this is compression of the carotid arteries. Brief compression, can cause dizziness, longer compression can cause loss of consciousness, and even a longer period of compression can cause death.
A major variable in play here is how severely the arteries are compressed. If only partially collapsed, the victim might have no problems. Severe and almost complete compression can cause loss of consciousness and death in short order. And anywhere in between. Significant and potentially deadly compression can result from strangulation–either manual or ligature–hanging, or an aggressively applied choke hold.
So, depending upon the nature, force, and duration of the compression, your victim could have no symptoms, become dizzy, lose consciousness, or die. Or could progressively move from one of these to the next. The time required for death could be a couple of minutes or many minutes if the compression is less severe or intermittent. As the victim struggled, he could intermittently release the strangle or choke hold and this would prolong the ordeal.
All these variable means that you can have it almost anyway you want. The killer could overpower the victim, render him unconscious in 20 seconds, and kill him in 2 minutes. Or the struggle could go on for many, many minutes. It’s up to you.