some good answers.
it is of my opinion that the aline should be verified against a second source with some regularity, and this should be documenting in your protocols. some places, it is q2hrs, some q4hrs
i am a proponent for using the opposite arm, but not just for my convenience.
when we occlude the artery on the side of the a-line, in theory we could promote thrombus formation as the stagnant blood allows for the platelets to begin their thing
second, the radial/ulnar flow is already partially compromised (thus, the infamous, inaccurate allen test), and we are furthering that compromise for awhile longer with same arm nibp
thirdly, there is can be a transient change in flow dynamics causing shearing force pulsations that may compromise the site further, ntm dampening issues with the monitoring system itself
fourth, excessive nibp measurements on same side may increase interstitial spacing near the site and affected extremity, ntm interfering with lymphatics--something we dont want to do cause possibly affecting immunity and possibly changing infectious statistics
all in all, it just seems more prudent, esp. with q15minute checks, to use an unaffected extremity when possible.
my 2 cents