You may want to try enalapril (0.25 mg/Ib twice a day) to see if it helps. It is an ACE inhibitor. If it helps, you know the rattie has a heart problem and add atenolol (1mg/Ib twice a day).
As you know, the lasix is used to remove fluid from the lungs, etc.
If the lungs are still full of fluid, then you likely need to increase the frequency of the lasix (1 to 2 mg/Ib twice a day) ... ie instead of twice a day, give it 3 or 4 times a day. The dose might also need to be increased. If you do this, keep a close watch for dehydration. Dehydrated ratties need to be rehydrated orally or by SQ injustion.
If they do have a heart problem, then you can check to see if their hearts are enlarged. If so, then they will also need to be on digoxin (0.0025 mg/Ib twice a day) to the other three medications.
(not a vet, info from the rat health care book and from experience)
Also, if they are dying with respir problems, you may want to consider having them put to sleep if they are suffering.
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