The more I talk to people, the more I realize they haven't got a clue -- and these are very educated people, very technology minded and sometimes even medical people.
First, the pump only pumps insulin. It's only a pump.
The pump holds a given amount of insulin. Some cartridges hold 200 units, some hold 300 units.
It pushes the insulin down the tubing and into a cannula -- a small piece of plastic tubing that is inserted into the skin with a needle. It's slightly worse than a regular insulin injection and loads better than a cortizone injection in the foot.
The pump doesn't do anything "automatically". You program it to deliver a basal dose. Mine is around 1 unit an hour, and the pump divides that into how every many times it delivers insulin an hour. So you get a fraction of that insulin every few minutes. This replaces the long acting insulins, which use chemical to slowly release the insulin.
You also have to enter a bolus for whenever you eat depending on your insulin to carb ratio. Thus, if I want to eat 40 carbs, I divide by 8, and program the pump to give me 5 units of insulin. Rapid acting insulin works about the same speed as metabolisming the average meal.
My goal, throughout the day, is to keep my blood sugars as stable as possible. If the basal amount is programmed correctly, my blood sugar will stay within 20 points, provided I don't eat.
If I calculate my meal correctly -- and there are variables on that -- my blood sugar should be in the 140 range two hours after a meal.
Therefore, what I do, is throughout the day, check my blood sugar with a normal, over the counter blood sugar device, and make sure that my blood sugars are in the right range.
There are several factors that can through it off ....
First, hormones, an being female, hormones especially can cause blood sugars to be erratic. Both internally produced and externally delivered hormones can change blood sugar.
Stress -- which causes hormone and adrenal production (isn't that a hormone), can also change blood sugar.
The make up of food -- high fat foods tend to slow absortion down, cause the insulin curve to be faster than the food curve -- though that can be fixed with an extended bolus. The pump has an extended bolus feature that lets the delivery of insulin be divided by a time period. Works great for pizza and mexican food.
Pure sugar has the opposite effect. I still get a short sugar buzz off of things like Lifesavers or Gummi Bears. In that case the food gives off sugar faster than the insulin works.
Just being off on the calculation. Let's say I go to Wendy's. Well, if the person serving the fries gives me 3 fries less than what has been measured and recorded in the FDA database, or 3 fries more, I'm going to be off on my carb to insulin ratio.
And sometimes the database is wrong, or the food doesn't have the same ingredients.
Yeah, it isn't fun, but better than the alternatives.