I think what LPN's can and cannot do is state, and even institution dependent.
Every ICU I've been in has had at least 1 LPN. I was also an LPN for four and a half years on the floor and regularly took the sicker patients. In my institution the four things LPN's cannot do is:
1) Spike and hang blood (they can monitor and take it down)
2) Take a verbal order, but no one is supposed to be doing that any longer. (In units such as Dialysis, they are allowed to in an urgent situation.)
3) Do the initial assessment on an admission and care plans
, but they can take a transfer, or an RN can co-sign their admit assessment and care plans.
4) Do the A and P on a SOAP note, but again, an RN can co-sign that as well.
Other than that, they can do it all where I work, push meds, hang meds, etc... There used to be about 7 meds they weren't supposed to push, but most LPN's are NAPNES certified so that covered them for med admin. They can certainly do ongoing assessments of the patient (and by ongoing, I mean after the very initial admission assessment) and chart their findings.
I oriented as an RN with two LPN's in ICU's for a bit, and let me tell you, they were a couple of the most knowledgeable nurses I've ever known. Every nurse is different.