CDO

Dear CDO users,
I'm having a fairly simple problem, yet I still haven't came to a solution.

I have a file with these variables:
var_a(time,latitude,altitude)
pressure(time,latitude,altitude)

and what I need is this:

var_a(time,latitude,pressure)

Is there a simple CDO command that does this conversion?

Thank you for your help,
Pavle