Welcome to the site, Fordgrl! Glad to have you with us.
Hmmm, good old deligation. I understand where you are coming from. If they are routine/patient has been there a day or two, stable, I would give the CNA's a time frame as to when you need the VS/BGM's, etc. Ex: 'I need room 201's BGM by 4:30 PM. If something should come up where you are not able to get it, could you please let me know? Thank you!'
Of course, if the patient is unstable....enough said.