Insulin in the Hospital

Why sliding scale alone is bad medicine

Sliding scale insulin treats a glucose that has already happened. You check a number, you give insulin for it, the patient eats, the glucose climbs again, and four hours later you do it all over. You are always behind. The chart looks like a saw blade: 320, then 90, then 280, then 70.

It persists because it is easy to order and requires no thinking. A type 1 patient on a scale alone will be in ketoacidosis by morning, because you gave no basal insulin and basal insulin is what suppresses ketogenesis. A type 2 patient on a scale alone simply spends the admission hyperglycemic.

The three components

Inpatient insulin does three separate jobs. They are held separately, and confusing them is how people get hurt.

Starting doses by weight

For an insulin naive type 2 patient, a reasonable starting point is a total daily dose of roughly 0.3 to 0.5 units per kilogram per day, split half basal and half nutritional, the nutritional half divided across three meals.

• 0.3 units/kg/day for the elderly, the thin, the renally impaired, or anyone with prior hypoglycemia. Insulin is cleared by the kidney, and a creatinine clearance under 30 makes every dose last longer than you expect.
• 0.4 units/kg/day for most floor patients.
• 0.5 units/kg/day or more for the obese, the insulin resistant, and anyone on high dose steroids.

If they already take insulin at home, start from the home dose, commonly 70 to 80 percent of the home basal if they are eating less here. Then adjust daily: the fasting glucose titrates the basal, the post meal numbers titrate the nutritional.

A worked regimen, 90 kg patient

Then read the numbers next morning. Fasting 240 means the basal is too low, so increase glargine by 10 to 20 percent. Fasting 90 with a pre-dinner of 260 means the basal is fine and the lunch dose is too small. Fasting 58 means cut the basal first.

Insulin types, onset, peak and duration

That last row matters most on nights. A drip has almost no tail. Turn it off without a plan and the patient has effectively no insulin on board within the hour.

The NPO patient

This is where the three components earn their keep. When the food stops:

• Continue the basal. Hepatic glucose output does not stop when eating stops. Holding basal in a type 1 patient manufactures ketoacidosis in someone admitted for something else. Many clinicians reduce it by around 20 percent when a patient goes NPO, but you reduce it, you do not cancel it.
• Hold the nutritional dose. No carbohydrate in, no prandial insulin. This is the only component that disappears.
• Keep the correction scale, switched from with meals to every 4 to 6 hours, at a reduced scale.
• Check the glucose more often, not less, every 4 to 6 hours. If the NPO period will be long, a type 1 patient needs a dextrose containing fluid running as well.

Holding insulin for procedures

The night before, give the usual basal or a modestly reduced dose. The morning of, hold all nutritional insulin, hold oral agents, and give basal reduced per your local perioperative protocol. Check a glucose on arrival to the procedure area and again in recovery.

Steroids

Steroid hyperglycemia is predictable and it has a shape: it is postprandial dominant. Morning prednisone drives the glucose up through the afternoon, peaks late in the day, and has often largely worn off by the next fasting check. So the patient whose 4 pm glucose is 340 may have a normal 6 am number, and if you answer that 340 by increasing the basal you will hypoglycemize them overnight.

Match the insulin to the steroid's time course. For once daily morning prednisone, the lunch and dinner nutritional doses need increasing, and NPH given with the steroid is reasonable because its curve roughly tracks prednisone. For dexamethasone or divided dosing the effect is flatter and the basal has to move too. Expect 20 to 50 percent more total insulin. When the steroid is tapered, drop the insulin the same day.

Tube feeds

Continuous feeding is continuous carbohydrate, so it needs continuous coverage rather than three meal doses. A common approach is basal insulin plus regular insulin every 6 hours, or NPH every 8 to 12 hours, with a correction scale every 6 hours alongside. Bolus feeds are simpler: treat each bolus as a meal.

Coming off an insulin drip

This is the highest yield item on the page. Intravenous regular insulin has a half life measured in minutes, so when you turn the drip off, insulin action is gone within an hour.

Give subcutaneous basal insulin 2 to 4 hours before you stop the drip. Glargine takes 2 to 4 hours to reach useful effect. That overlap is the whole point: you want the basal working before the drip stops, not after. Stop the drip and give the glargine at the same moment and you leave several hours with no effective insulin on board. In a type 1 patient, or anyone just out of DKA, that gap restarts ketogenesis, and you will be treating again the ketoacidosis you spent the night fixing.

DKA and HHS in outline

Both are treated with fluid, insulin and potassium, in that order of priority.

1. Fluid first. Isotonic crystalloid, generously, then reassess. Correct the deficit over a day, not over an hour.
2. Check the potassium before the insulin. Below about 3.3, replace it and hold the insulin, because insulin drives potassium intracellularly. Total body potassium is depleted even when the measured level looks normal.
3. Insulin infusion per your protocol. Do not chase the glucose with boluses.
4. Add dextrose when the glucose reaches 200 to 250, and keep the insulin running. This is the step people get wrong. The insulin is not there to lower the glucose, it is there to shut off ketogenesis. Change to a dextrose containing fluid so the insulin can continue without causing hypoglycemia.
5. Find the trigger. Infection, infarction, pancreatitis, missed doses, a failed pump.

HHS has enough insulin to suppress ketogenesis but not enough to control glucose. The glucose and osmolality are very high, there is little or no gap, and mental status changes dominate. Fluid is the main therapy, and the sodium and osmolality come down slowly.

Hypoglycemia

Treat below 70. Treat urgently below 54.

• Awake and able to swallow: the 15-15 rule. 15 grams of fast carbohydrate, meaning 4 ounces of juice, 4 glucose tablets or a tube of glucose gel. Recheck in 15 minutes and repeat if still under 70. Then a snack with protein and complex carbohydrate so it does not fall straight back down.
• Obtunded or NPO with IV access: 1 amp of D50, which is 25 grams of dextrose, intravenously. Recheck in 15 minutes.
• No access and cannot swallow: glucagon 1 mg intramuscularly, and get access. Warn the nurse the patient will probably vomit. Glucagon mobilizes hepatic glycogen, so it works poorly in the starved, the alcoholic and the patient in liver failure.

Then find out why. Was the tray never delivered? Was nutritional insulin given to someone who did not eat? Did the feed stop? Was a sulfonylurea continued alongside a full insulin regimen? Sulfonylurea hypoglycemia is prolonged and recurrent, and those patients need continued observation, not one amp and a pat on the head. See Common Night Calls for how this presents overnight.

Discharge insulin planning

Start this on day two, not on the morning of discharge. The inpatient regimen is not automatically the discharge regimen, because they are going home to different food, different activity and no nurse.

• Check an A1c if there is not a recent one. It tells you whether the home regimen was already failing.
• Well controlled at home and admitted for something unrelated: resume the home regimen.
• A1c high: they need a change and this admission is your chance. Simplify. Basal once daily plus oral agents is far more likely to be taken correctly than a four injection regimen in someone who has never used one.
• Confirm they can afford and obtain what you prescribe. An analog they cannot pay for is worse than NPH and regular that they can.
• Confirm they or a caregiver can draw up and inject, and watch them do it before they leave.
• Send them with a meter, strips, lancets, and what number to call for, and arrange follow up within one to two weeks.

Write the discharge regimen in the same three part structure you used in hospital. The next physician should see at a glance what is basal, what is nutritional and what is correction.