I agree with Carl. I was several months into testing when I started a sliding scale, so I had a massive amount of data and never had to shoot over a 1.25u. I am still eyeballing a u40 syringe, so it is possible. My cat's numbers never go over 200 anymore, except during weather events that aggravate his arthritis, or anything that makes him stress.
My vet is a very cautious woman, and had me start on 1.0u regardless of how high his BG was, which proved to be just what was needed. Just like Carl, I took a non-vet approve step and raised his shot to 1.10u and then presented her with the numbers. She let me take over shot adjustments when I showed her what we had done by testing with variable shots.
For my cat, Every Day Is Different! Eventually he would fall into a pattern and even started to regulate his own drops in BG with food. He even turned his curve upside down at one point, and we started getting lower and lower numbers.
My current sliding scale goes like this:
3oo+ - 1.0u
200-299 - .75u
170-199 - .50u
150-169 - .25u
130-149 - .10u
100-129 - Skip it, or try a .10 ONLY if I'm going to be home.
Only a few months ago, his shots on each of those scales would have been .25-.50 higher. His relationship to his insulin changes constantly, and he drops into 2-digit numbers about 2 hours into the shot. He's never hypoed. These tiny shots don't have the duration the larger shots get, but now if I waited for him to reach 200, it would take, at a minimum, a day and a half. He's always been a tiny eater, so he doesn't get the solid backing of food to support a really large shot.
I can't stress enough how much testing I did to arrive at this. You will know more about how food and insulin and outside and inside influences affect your cat, than you probably ever thought you would know. I believe that the longer he stayed in the low normal numbers the quicker he healed. Even the habits he had when his BG was really high (400-500) started to show up on numbers in the 200s, meaning his body was now recognizing 200 to be too high.
On a sliding scale, BG numbers will start to be normal very very fast. So testing is critical. If you free feed (leaving food out when you aren't there), you might notice that food spikes play a part in the BG, depending on when your cat ate. For my cat, at his advanced age (18), I wanted his daily life to remain as normal as possible. So he often eats before I get home, so I have tested to establish his general food spike number, and factor that number into his shots.
Check daily for the 5 P's (pooping, peeing, playing, purring, and preening). Stress from constipation kept my cat in the high BG's for a long time. I also got glucose urine strips to check in between shots to figure out his renal threshold (270), so any number below that was at least keeping his kidneys sugar-free.
Lastly, a sliding scale is lot of "Let's see what happens if I do this" method. if you are going to start a sliding scale, I would start at a 1.0u shot, even if your pre-shot number is 500+ for a least a week, testing, at a minimum, at preshots and (+6). Start on a day when you can be home all day. That will establish a base where you can start adjusting numbers, then only adjust .25 at a time. You will start to see how aggressive you can take the shot as you get to know how your cat operates.
Good Luck!
She grab her with her teeth and wouldn't let go and was pulling back and forth. I grabbed darma. Lucky Darma didn't have a wound. I don't know why either??? But I order 2 fences and Have one now, which is okay. Just got it after that fight today. Darma is a little fat and can't fight real well. Also, my cats don't know how to fight.
:shock: 
