Attack is the best defence! I read my emails in the morning and figure out whether there's some action for me. When I go and get my second coffee, I drop by the PM's office and have a short chat with him.

Where I am in the projects, whether there's stuff from other tasks or unexpected actions, how long that might take, whether schedules are still OK, whether I need him to take care of some customer communication, these things. Usually less than 5 minutes.

The kicker is that he mostly doesn't interrupt me because I instead interrupt him - unless he is highly busy, in which case he just says "sorry, later", same as I would do.

It's a win-win because I can schedule the interruptions while he enjoys that he doesn't have to ask around.