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When undergoing cardiac surgery, the heart is disconnected from the blood circulation and blood is passed through a heart-lung machine and cooled so that the body temperature of the patient is reduced.

I understand that this would slow down metabolic processes but how exactly does slowing down these processes benefit the patient?

Thanks for answering!

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As you mention, hypothermia is routinely induced during cardiac surgery. There is a blog post including a photo of a heart being cooled with ice chips here: https://www.heart-valve-surgery.com/heart-surgery-blog/2010/10/17/ice-cardioplegia-open-heart-surgery/

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The primary therapeutic benefit of deliberate hypothermia was long thought to be, as you say, the slowing-down metabolic processes, which reduces the amount of oxygen needed by the brain and other vital organs (source). Cooling the blood during open heart surgery therefore allows the operation to be performed more slowly (2-4 hours).

However, according to this open-access article on the benefits of therapeutic hypothermia for cardiac surgery:

the widely held notion that hypothermia protects because lower temperatures slow metabolism is not completely accurate. Recent research has shown that hypothermia can alter a plethora of cell death and cell survival pathways including gene regulation resulting in the inhibition of apoptosis and inflammation and the up-regulation of anti-apoptotic or trophic factors.

So basically it does slow down the metabolic processes but it also reduces inflammation and cell death.

After surgery, rewarming needs to be done slowly to maximise the chances of recovery (source).

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  • $\begingroup$ Does the lowered amount of oxygen used by organs other than the heart really matter? Surely they have a good supply of oxygen due to the heart-lung machine. $\endgroup$ – Aswin Abraham Dec 5 '17 at 20:30

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