There was, however, a door knob on the outside. Angel had no idea that there was someone trapped inside or he would have attempted to do something a little stupid and a little heroic. (Kicking down a door while still suffering from broken ribs? Painful and stupid.)
Not knowing that was the case, the former vampire settled on polite knocking. The hospital at this point was filled to capacity with those who's medical needs were greater than his, not to mention that Angel suffered from a fairly severe hero complex. There were times when he missed being a vampire almost as much as he enjoyed walking freely in the sun (which was a lot).