Regarding overhydration, here's the info from felinecrf.org. I can't recommend that site more highly. Nor can I recommend the support group more highly!
Overhydration and Fluid Retention
It is possible for cats to be overhydrated, i.e. given too much fluid, either via IV or sub-Qs. Some vets say it is not possible to
overhydrate a cat using sub-Qs, but believe me, I've heard of plenty. Overhydration may also cause
hypertension.
Cats with heart problems can also develop problems with body fluid build up. If your cat is receiving sub-Qs and has undiagnosed heart problems, it may be that the amount of fluid you are giving, that would be fine for most cats, is too much for your cat. It is also possible for cats with heart disease to develop fluid retention even if they are not receiving sub-Qs.
Fluid may collect:
- in the lungs (pulmonary oedema)
- around the lungs (pleural effusion)
- in the abdomen (ascites).
If your cat:
- feels "squishy" when you stroke him or her
- has loss of appetite (which may be caused by the fluid pressing on the stomach causing a feeling of fullness)
- appears to be gaining weight rapidly or suddenly. Most people are delighted when their CKD cat gains weight, and certainly if weight gain is slow and steady, this is good news. However, if your cat gains weight very quickly (I have heard of people who are delighted because their cat has gained 2 lbs in a week, a phenomenal rate of weight gain as a percentage of the average cat's size), this may be a sign of fluid build up.
- starts coughing and/or develops a nasal discharge
you need to see a vet quickly.
If your cat starts breathing with the mouth open or develops a limp with the affected leg cold to the touch, your cat may be in severe
congestive heart failure or may have an
arterial thromboembolism. These are medical emergencies and you need to get to a vet as quickly as possible.
Do not give sub-Qs to a cat exhibiting any of the above symptoms until you have spoken to your vet. You should also never give a cat sub-Qs until the fluids from the previous session have been absorbed.
The
Heart Problems page has more information about fluid build up and congestive heart failure, including symptoms, causes, what happens, and how to treat.
If your cat does exhibit these problems and you can afford it, I would recommend a visit to a feline cardiologist to discuss future treatment options for your cat. It may still be possible to give sub-Qs in the future if your cat needs them, but it is a careful balancing act between the needs of the kidneys and the needs of the heart.
If the problem was caused by giving too much fluid, you may find that reducing the amount or frequency of sub-Qs given in the future prevents this problem arising again; so speak to your vet about this. The
Subcutaneous Fluids page has information on amounts and frequency of fluids.