Surgery and insulin

I am having an op with a general anaesthetic, I have to go in for 4pm and they have said don't eat from 12 noon. I take my BI at breakfast and bedtime. Should I reduce my BI, and if so at which injection? Should I test before noon and if low, eat something to bring me up to normal BG and if high, correct with QA? Should I time breakfast for about 8am so that there is 4 hours until 12 and if necessary eat something. My actual op will probably be nearer 5pm. Thanks for any advice.

Another consideration is also how long you will be out to it. Helen