To add to the discussion in the comments:

There is also the practice of not using anesthesia on infants when undergoing medical surgery.

Anesthesia is hard to do even on adults, harder on children, and very difficult on infants. Not accidentally killing one is quite hard.

So, for a long time we just didn't. I think some countries still don't, but can't remember.

The idea really gets back all the way to philosophy. If you can't remember if you were in pain, did you get hurt? And then you add in the medical problem itself, the duty to do no harm, the difficulties, etc. The conclusion was to just not use pain meds.