Eli5 Why do people with grade 4 pressure ulcers not bleed to death ?

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Title.
They have open wounds that can be as deep into the flash as to the bone. But they don’t bleed to death. Why?

In: 6

Usually unless you break a major vein or artery, its going to take a long long time to bleed to death.

Pressure ulcers are caused by pressure cutting off the circulation, so they don’t tend to bleed.

To check if a red pressure area is a grade one, or just at risk, nurses will press it with a finger. If it blanches, it isn’t a pressure ulcer.

Source : I’m a grumpy old nurse.

Blood moves through arteries and veins, like water through the pipes in your wall. A pressure “ulcer” is more like an area of dead soft tissue. Imagine if your wall made of drywall was damaged and you had to pull apart the damaged drywall. The pipes are still there holding in the water inside the wall. If you were careful taking it apart you would not expect water to start spraying out.

Another way of asking this questions is why you don’t bleed to death when you a surgeon cuts into your body. Of course there is a little bit of bleeding which is cauterized. But even without cauterizing there is surprisingly little bleeding during many surgeries. The reason is that the surgeon is not cutting the large blood vessels and so the blood stay in where it belongs.