A list member wrote:

"If you lift up their skin and it immediately springs back, they are not dehydrated substantially.  If it takes awhile to return to normal, then they are dehydrated."

We all fall prey sometimes to a tendency to reverse logic. In reality, if you lift up the skin and it *does not* immediately spring back, the kitty is suffering dehydration roughly equivalent to loss of 5% of their body weight in water! However if the skin *does* spring back, he may still have lost up to 4% of his weight (about 125 ml for an 8-lb cat, definitely enough to need replacing)!

Another test that's used is to check for slickness of gums, but this also only shows 5% dehydration. Any cat failing either of these tests needs immediate help!

The way most of us gauge the need for fluids is by knowing our cat. Compare how he acts/feels before and after sub-q's. Chances are that before sub-q's his activity level will be low, he may have a sad, headachey look in his eyes. He won't show any interest in food even though he probably hasn't been eating. He may just want to curl up and hide. Dehydration was described by a human kidney patient (spouse of a listmate) as like a bad hangover. After sub-q's a well-maintained crf kitty will probably perk up, possibly get an appetite or want to play. You'll learn to tell the difference.

My goal was always to schedule sub-q amounts and times to beat the "hangover". If the effects of a given dose (say 100ml) don't seem to last the allotted time until the next scheduled treatment, I'd either give a bit more (perhaps 125ml) or give it sooner. Experiment with timing/doses until you find the combination that seems most comfortable.

With Coco the progression was to increase the dose until it passed 150ml, which was the most I wanted to give her at once. At that point I switched to smaller doses twice daily, spaced roughly 12 hours apart. Since workday schedules sometimes don't allow equal spacing I'd adjust the split to roughly match the duration of time until the next treatment.