I only know what I’ve seen working in clinical pharmacology. At first, the pca pump is set very conservatively low and there is a demonstrated psychological/placebo effect from pushing the button, whether or not drugs are delivered. (Rather like the “close door” button on the elevator that doesn’t do anything but makes you feel like you’re doing something). Most MDs put a lot of stock in this placebo, so if you aren’t getting real relief, don’t be shy about requesting a higher delivery dose.