Is is safe to have lip filler before going into hospital for a surgery under general anaesthetic?

Go right ahead!  There is no problems or contraindications for you to have filler prior to general anesthesia.  Good Luck with everything

There is likely no risk to you if this is done, especially if done with a cannula, however, i suggest waiting. there is likely no reason why you would need to do this prior to having general anesthetic which would need access to your throat.  I suggest waiting till after.  Best, Dr. Emer.

I would generally advise against any elective cosmetic procedure just prior to a medically necessary procedure to avoid any delay or interruption of medical care. 

 Thanks for your question. I don't see why this would be a problem.  You certainly don't have to worry about any kind of an interaction between the filler and the anesthetic. Best of luck to you!

You will not have any problems with your filler if it is done at least a week or so before the general anesthesia. You want the filler to settle  before the lips and mouth are manipulated which is frequently done with general anesthesia.