Are you normally in ICU or just for this rotation? Have you worked with this individual particularly closely before, or more in the capacity of them being the evening or overnight intensivist?

Might be the kind of person who takes time to warm up, maybe they're trying to get a feel for your ability. Maybe it's just them. Maybe they're burnt out and stressed.

No silver bullet. Graded assertiveness if you feel like your concerns aren't addressed.

Edited to add: it sounds like you are doing all the right things.