In my hospital and in the discussions we have with the other chiefs of surgery at the other children's hospitals, it's nurses. It's nurses who keep our ORs and our recovery rooms open and nurses who staff hospital beds, particularly in critical care areas.
We can have a child waiting for surgery, we can have a room and we can have a surgeon and an anaesthetist, but without a nurse to staff a bed for that child to go to after surgery, we can't start that case. Obviously you can see the shift in the allocation of resources away from children who need beds after surgery, which means that we use that time in other ways, but it's usually to treat children who don't necessarily need a bed after surgery.
Some of the other issues around space and equipment are important, but I would have to say that in my hospital, and in most of the children's hospitals across Canada, it is the nurse human health resource that is the limiting factor.