Short answer: map to any standard concept that aligns with your data, and if none, use SNOMED concepts.
Infusion products that are not pharmaceutically active are indeed considered devices in OMOP conventions. Same goes for Albumin — blood products are subset of tissue transplants.
As for what Standard concepts to use — it’s hard to say. There is no convention yet, because conventions come from established practices, and there is not many observational research done on electrolytes and blood transfusions.
For that reason, basically ALL device concepts in vocabulary are currently standard and map to self. There used to be a Device workgroup, which worked on establishing a standard, I’m not sure if it is currently active.
SNOMED developers themselves face a similar issue, and there’s hoping they will establish standards first.