Perioperative Insulin Management

Perioperative insulin management aims to keep glucose at 6 to 10 mmol/L (accepting up to 12 mmol/L), avoid ketoacidosis in type 1 diabetes, and prevent both hypoglycaemia during fasting and hyperglycaemia from surgical stress. A good plan starts at the preoperative visit.

Priority. Place people with diabetes first on the list to limit fasting time.

Risk of poor control. HbA1c over 69 mmol/mol (8.5%), missed meals, major surgery, and emergency admissions raise the risk of complications.

Type 1 diabetes. Never omit basal insulin. A missed meal needs either a reduced insulin plan with glucose monitoring or a variable rate infusion.

Intravenous infusion with glucose and potassium. For type 1 diabetes when more than one meal will be missed, for poorly controlled diabetes, and for major surgery.

Subcutaneous insulin. For type 2 diabetes on insulin with a short fast, adjusted as set out in the dose section.

Non-insulin drugs. - Metformin: hold on the morning of surgery for major procedures; continue for short fasts when eGFR is 60 or more. - Sulphonylureas: omit on the day of surgery. - SGLT2 inhibitors: stop 3 days before (4 days for ertugliflozin) and restart when eating. - GLP 1 receptor agonists: follow local anaesthetic advice about holding; weekly agents are often held for 1 week. - DPP 4 inhibitors and pioglitazone: continue.

Basal insulin (glargine, detemir, degludec). Give 75 to 80% of the usual dose the evening before (for evening dosing) or on the morning of surgery (for morning dosing).

Isophane insulin. Give 50 to 75% of the usual morning dose, and the full usual evening dose the day before.

Premixed insulin (twice daily). - Evening before surgery: give the usual evening dose. - Morning surgery: give half the usual morning dose on the morning of surgery if the patient is not on a variable rate infusion, check glucose hourly, and restart the usual doses with the first meal. - Afternoon surgery: give half the usual morning dose with an early light breakfast, or follow local practice.

Mealtime insulin. Omit while fasting; restart with the first meal.

Variable rate infusion. Use the scale in the infusion article, with 5% glucose and potassium chloride 0.15% (about 20 mmol/L) running at 80 to 125 mL/hour, adjusted to fluid status. Check glucose hourly.

After surgery. Restart subcutaneous insulin when eating, with the first dose given 30 to 60 minutes before the infusion stops. Resume metformin when eating and kidney function is stable, and SGLT2 inhibitors only after oral intake is normal.

Special groups. - Kidney impairment: reduce insulin doses by 25% and check glucose more often. - Liver disease: lower doses with closer checks. - Pregnancy: specialist-led plan, often with intravenous insulin. - Steroid therapy: add correction insulin and expect higher afternoon glucose. - Emergency surgery: start the variable rate infusion and treat ketones if present.

Monitoring. Capillary glucose hourly during infusion and during surgery over 2 hours, otherwise every 2 to 4 hours. Ketones if glucose is over 14 mmol/L or the patient is unwell, in type 1 diabetes.

Hypoglycaemia. Treat glucose under 4 mmol/L with 10% glucose 150 to 200 mL intravenously or 20% glucose 75 to 100 mL, and recheck at 10 to 15 minutes.

Stopping. Stop the infusion once the patient eats and subcutaneous insulin has been given.

Referral and escalation. Refer to the diabetes team for HbA1c over 69 mmol/mol, ketones of 1.5 mmol/L or more, recurrent glucose over 12 mmol/L after surgery, or inability to eat for more than 24 hours.