http://www.rocknrescue.com/acatalog/Russ-Anderson-Litter-Wheel-With-Frame.html
It has a big turn screw in the center, and attaches to the rescue basket. IMO, it's a pain in the posterior. Because then you're lifting the patient and the wheel. The basket is light as a feather, as far as rescue baskets go anyway. Then there is the deal of carrying it in, it ain't light. 30lbs may not be heavy where you stand, but carrying it for several hours isn't a task anyone wants. It may seem the smart thing to put all your shit in the basket, and walk it in attached. No, slow going, it's slow going with a patient. Everything that goes in, except the basket, is in backpack form. Ropes, rigging, haul systems, medical stuff; all in nifty bags to ease access and necessitate quick storage, when you have to set up, haul, tear down and move to the next location.