It depends what you want to slice, if it's a button you have to slice exactly how it is showing, and if it is background then you have to slice according to your page though it includes bit of html here.
content area, navigation bar, buttons and all plays some role to your 1920px you have to slice exactly what is given.
See this how every single element is sliced in a manner its just an example dont follow this every designer use their own way, its an example only: Coding from psd to xhtml
show us your screenshot so better we can help/suggest you, that what you have to do.