If the basal insulin is intermediate-acting
The intermediate-acting insulin neutral protamine Hagedorn (NPH) is usually given twice a day because of its profile (Table 1).
- On the night before surgery, the full dose of NPH insulin should be taken, unless the patient will now skip a nighttime meal because of taking nothing by mouth, in which case the dose can be decreased by 25%.1
- On the morning of surgery, since the patient will be skipping breakfast and probably also lunch, the dose should be reduced by 50%.3,4
Special situation: Premixed insulins
Premixed insulins (70/30, 75/25) are a combination of intermediate-acting insulin and either fast-acting or short-acting insulin. In other words, they are combinations of basal and prandial insulin. Their use is thus not ideal in the preoperative period. There are two options in these situations.
One option is to switch to a regimen that includes long-acting insulin. If the patient is admitted for surgery, then the hospital staff can change the insulin regimen to long-acting basal insulin. A quick formula for conversion is to add all the premixed insulin doses and give half as basal insulin on the morning of surgery, similar to the scenario above for the patient with long-acting basal insulin that was out of proportion to the prandial insulin injections.
For example, if the usual regimen is insulin 70/30 NPH/Regular, 60 U with breakfast, 30 U with dinner, then the patient can take 45 U of insulin glargine (which is half of 60 + 30) in the morning or evening before surgery.
Another option is to adjust the dose of pre-mixed insulin. Sometimes it is not feasible or economical to change the patient’s premixed insulin just before surgery. In these situations, the patient can take half of the morning dose, followed by dextrose-containing intravenous fluids and blood glucose checks.
We recommend preoperatively giving at least part of the patient’s previous basal insulin, regardless of the type of diabetes, the type of surgery, or the fasting period.
STEP 3: STOP THE PRANDIAL INSULIN
Prandial insulin—given before each meal to cover the carbohydrates to be consumed—should be stopped the morning of surgery.3,4
WHAT ABOUT SLIDING SCALE INSULIN?
Using a sliding scale alone has no known benefit. Although it can be a quick fix to correct a high glucose level, it should be added to the basal insulin and not used as the sole insulin therapy. If a sliding scale is used, fast-acting insulin (aspart, glulisine, lispro) is preferred over regular insulin because of the more rapid onset and shorter duration of action.
Patients already using a supplemental insulin scale can apply it to correct a blood glucose above 200 mg/dL on the morning of surgery.
MAINTENANCE FLUIDS
As long as glucose levels are not very elevated (ie, > 200 mg/dL), after 12 hours on a nothing-by-mouth regimen, provide dextrose in the IV fluid to prevent hypoglycemia (eg, the patient received long-acting insulin and the glucose levels are running low) or to prevent starvation ketosis, which may result in ketones in the blood or urine. We recommend 5% dextrose in half-normal (0.45%) saline at 50 to 75 mL/hour as maintenance fluid; the infusion rate should be lower if fluid overload is a concern.
POSTOPERATIVE INSULIN MANAGEMENT
Once patients are discharged and can go back to their previous routine, they can restart their usual insulin regimen the same evening. The prandial insulin will be resumed when the regular diet is reintroduced, and the doses will be adjusted according to food intake.