Personal experience (I gave a lot of insulin when I was working...but it's a whole different ball game to figure out doses on yourself- LOL
Long acting (Lantus in my case) is just what I need to keep my blood sugar more level when nothing else
is factored in. Sliding scale (or when people do their own- insulin to carb ratios ) cover anything added....meals, IV dextrose if NPO, etc.
If my blood sugar is say, 70mg/dl at hs, I still take all
of the Lantus (I've gotten some grief over this in the hospital- and I understand it's coming from a POV of being safe.....but no two diabetics are alike) - and eat a snack.
If my blood sugar is 200mg/dl at hs, I take the Lantus, and
take sliding scale - even if I'm going to bed. If I have a snack, the carbs are less.
Most diabetics who use carb counting and the insulin:carb ratio to determine insulin dose are REALLY good at it (or they just go with the "generic" sliding scale which isn't that great-doesn't take into consideration the # carb grams consumed- just the blood sugar
....and that makes a big difference). The I:C ratio is used to cover meals BEFORE they are eaten (though in the hospital, I would wait until JUST after, since I never knew how much I'd be able to choke down). Fast acting (NovoLog, HumaLog......NOT regular, though some people do use that for budget reasons) is designed to kick in faster than regular so the spike isn't as high after eating. It takes a while to figure out the ratio- and it can change w/illness.
Once you get something figured out with the orders for one patient, someone else will show up with a totally different set of numbers. And, I've given 100u Regular IV....for a blood sugar in the 400s, asymptomatic- but had high ketones..... I dragged the doc down to the room with me on that one