Note that responsive web design is different from adaptive web design! Don't confuse the two -- they're not interchangeable terms. Responsive basically sends all your materials over, and lets CSS and JS on the browser sort out which things to use. Adaptive basically has the server asking the browser what it supports (screen dimensions, control devices, etc.) and then just sends out pages customized to those capabilities.
Adaptive would have to send an update to the server if display dimensions (window size, mobile device orientation) changes. You could have a hybrid system where the first page to a browser is responsive, the browser sends back information about its capabilities, and subsequent pages in the session are adaptive (customized to the device). I haven't seen such a setup, but it should be possible.