The short answer is yes, absolutely, they work in ICU's, but the extent that they actually practice "critical care medicine" varies widely. The issue basically comes down to whether the ICU staffs intensivists...if so, the hospitalist will usually have a much more limited role. On the other end of the spectrum, at some places the hospitalist will do everything from placing lines to managing the pressors and so on. Where I am now, we have no intensivists (we have pulmonary/critical care specialists who consult on patients, but their role rarely goes beyond the lungs) so as hospitalists we have to handle the other critical care issues, obviously in consultation with other services. We usually don't do procedures outside of emergent lines (surgeons do the routine ones), but again, that's certainly not true at all places.