Kuushou = Vaacum palm (english dub) where he send a pressure wave, he did against Kisame.
You must be talking about Kaiten.
They might seem the same concept, but the very basic objective are totaly oposite.
Kaiten, is a defensive move, where you expel chakra to parry an attack
Not only that, it use a large ammount of chakra for it.
Rasengan, is an direct attack move, that is nearly self sustaing and use somewhat alot less chakra then Kaiten, simply because once its made, you can keep the rasengan out as long you wish, oposed to kaiten where you got to keep pumping a giant ammount of chakra to spin.
Also the rotation is totaly diferent, Kaiten only spin one direction
So even if you make a miniature Kaiten to Rasengan size, it wouldn't be effective.
Lastly if you tried to Maximize Rasengan to Kaiten size, it wouldn't be able to be used, as Rasengan is FULL of chakra, spinning on all directions..
The chakra spinning inside would hurt YOU.
Kaiten is just a skin of chakra
Only thing they have in common, is they only use only chakra(non elemental) and no seals.
"Chile is a thin and tall country"