Lyren wrote:Hmm, isn't something like this already done for open-heart surgery? Could somebody explain the difference? I am a bit confused about this.
This is what I remember from the last open-heart surgery I was involved in (this was third year of medical school, about four years ago). Some of the details might be a little glossed over, but the idea is the important thing.
- Tubes from a heart-lung bypass machine are connected up to the great vessels of the heart after the chest is opened up.
- The heart is isolated and infused with a cold fluid called cardioplegia mixed with cooled blood. Cardioplegia is a compound with, among other things, a whopping amount of potassium which in very high doses directly delivered to the bloodstream will stop your heart. (Don't worry. Your body only keeps as much potassium from your diet as it needs, and discards the rest in your urine.)
- Clamps are applied and the blood is redirected from venous return into the heart-lung bypass, and arterial oxygenated outflow from the bypass is directed into the aorta (the main trunk artery). The bypass operates just as it says -- it works to oxygenate the blood, as the lungs would, and pump it out through its artificial chambers. The whole apparatus is kept very cold to minimize metabolic damage, because this is not a physiologic setup. In fact, because the heart is not being properly oxygenated with this technique (the coronary arteries are usually well upstream of the clamps), if it were not kept cold, the heart would suffer irreversible damage. There are now some studies to suggest that under some circumstances you can do this at body temperature, or at room temperature, but this is controversial.
- The surgery is done.
- Afterwards, the venous return shunt is disabled and blood is allowed to re-enter the right side of the heart and pump out through the aorta as the heart-lung bypass itself drains into the aorta and completes. The body is warmed up, and the connections removed in preparation for closing up.
As you can see from all of this, the patient's heart might be stopped, but the rest of the body is not, so this doesn't really quite qualify as the same thing.
If people want some rather weighty reading, here is a study on optimal temperatures for cardioplegia done by the Veterans' Administration health network. Warning, it's rather technical.
http://www.va.gov/vatap/pubs/cardioplegia.pdf
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