There were two ways that we knew Evan needed a dieretic - when he was in the hospital he retained lots of fluid (puffy feet and hands for example) and his respiration rate would go up when he built up excess fluid in the lungs. A dose of Lasix would bring his respiration rate back down, and his sats would stabilize. As Christy said, Lasix is nasty, so our docs wanted Evan off it ASAP. However, he did not seem to do as well on the aldacteside (more fluid build up, etc) and his bloodwork showed he was tolerating the Lasix well, so we kept him on it. I was surprised they took him off cold turkey, but he did not retain fluid, urinated OK (sometimes kids become dependent on dieretics to urinate), and had grown his way into a better place with his lungs, so he did not need it anymore.
To summarize, if you try stopping the dieretics, I suggest you monitor lung function (respiration rates and sats), urine output, and fluid retention (puffiness of hands, feet, face) and if none of these things change, your child is ready to go without. Those were the things we looked at. Good luck!
Laurie - Mom to Evan (the E-man), 27 week preemie, born 2-23-02, trached at 3 months for severe BPD. Vent dependent until 10 months, G-tube placed at 17 months, oxygen dependent until 2 years, 3 months, decannulated 6-27-04 at 2 years 4 months. The most enthusiastic, positive person I've met.