Originally Posted by
Liba
The POC is included in your cabin baggage allowance.
I would read this as "you can carry on the POC in addition to the regular stuff you can carry on". I admit it's ambiguous, though.
But I'm not aware of any other airline regulation that forces medical equipment to displace other carry on items.
Your "we'll pack what he needs" plan is a good one. Allow plenty of time, take lots of deep breaths, and assume ignorance rather than malice.