necrosis in thinner body parts (i.e., ears, fingers) vs. thicker parts (i.e., arms/legs)

Wondering if gangrene develops more quickly in thin body parts (such as the ears, using ears as the example) when bloodflow is totally cut off, than in thicker parts such as the arms and legs. The thinner ears would seem to be easier to begin dying off if there were no bloodflow to them, but the arms and legs, despite having more blood vessels servicing them, also have more oxygen-hungry cells that need O2.

I had read that limbs can go up to 1.5 hours with a tourniquet without needing amputation. Wonder how long the thin ears could survive without blood?

To be clear, necrosis is tissue death. A number of no good, very bad, often antibiotic resistant bacteria can cause tissue or fascia to liquify.

Ischemia is tissue death due to loss of oxygenation. Ears have two separate arteries supplying the top and bottom of the ear; feet and hands also have a back-up blood supply.

A region with less tissue will be more damaged given the same amount of tissue damage. So the ears and feet are at risk — toes much more so than thighs.

The most common cause is a foot infection is in a severely diabetic patient. Diabetes causes damage to both small nerves and blood vessels. Many diabetics get unwanted amputations since they cannot see the bottom of their feet or toes easily, do not feel when infection arises, and are resistant to treatment since blood supply is already compromised and antibiotics rely on the blood supply to get to the site of an infection.

Ear infection tends to cause very visible swelling and is much more likely to be treated early. I don’t know if bad diabetes causes ear numbness — Perhaps occasionally, but classically it causes “stocking and glove” paresthesia instead.

The amount of time needed to cause irreversible tissue damage is hard to study. An estimate of six hours is often used. No doubt it is much less in some situations.

If brain tissue dies in 5 minutes without O2 and other tissue can last hours, is the brain matter much more sensitive to lack of oxygen?

The six hour figure is a guideline for limb ischemia. It is a “generally agreed upon” time by vascular surgeons. But people are different and it is not going to be exact for any individual.

If someone is having a blood clot to the brain or heart blocking flow, time is obviously important. The sooner flow is restored, the lower the chance of irreversible damage. The amount of time to irreversible damage is controversial and hard to measure. Medicines to break up clots can cause severe bleeding and death. They are not given lightly, but current guidelines suggest benefit for a few hours after symptoms begin. Brain tissue is pretty sensitive, and obviously can have more severe effects. But five minutes of ischemia (not sure where this number comes from) is likely reversible in some situations. Specifics matter.