just another thing to note. Having just spent a brief amount of time in the ICU myself I originally had my cuff on the same arm as the a-line. It HURT a lot so I asked them to move it, despite the a-line they were still doing hourly cuff pressures on me, I'm young, 24 years old, average size but that cuff hurt a lot more than I ever thought it could and my other arm had IV's with fluids which would burn until the cuff released.
The things you don't know until you experience them. I never did ask why they needed both, I did ask for the a-line to come out ASAP :-)