Name: Diabetes and Surgery: Keeping Your Sugar Safe | Dr. Tamer Elalfy
Creator: Dr. Tamer Elalfy

Diabetes and Your Operation

Diabetes affects every stage of surgery: wound healing, infection risk, kidney function, and recovery. High blood sugar around surgery increases wound infection, while low blood sugar under anesthesia can go unnoticed. You know your diabetes better than anyone, so the best plans are made with you, not for you. The key message of this guide: your diabetes plan for surgery will be written down for you. Follow it exactly, check your sugar, and tell the team early if you feel unwell.

Preparing for Surgery With Diabetes

Before planned surgery, the aim is a long-term sugar measure (HbA1c) below about 8 to 8.5 percent where possible. Improving control should not delay urgent or cancer surgery.
Around surgery, the usual target is a blood sugar of about 100 to 180 mg/dL (5.6 to 10 mmol/L).
You will usually be placed first on the operating list, so you do not fast longer than needed.
Bring your medicines, your insulin, your glucose meter, and your written plan on the day.
Check your sugar more often in the days before surgery, and on the morning of surgery.

Your Medicines Around Surgery

Each diabetes medicine has its own rule. Hospitals follow one protocol, and guidance differs between countries, so your written personal plan always comes first. The usual approach is:

Metformin

Before surgery: Usually omitted on the day of surgery; longer if there are contrast dye or kidney concerns
After surgery: Restart when eating and drinking, if kidney function is normal

Sulfonylureas, for example gliclazide

Before surgery: Omit on the day of surgery, because of low sugar risk while fasting
After surgery: Restart when eating normally

DPP-4 inhibitors, for example sitagliptin

Before surgery: Often continued; follow your protocol
After surgery: Continue when eating

SGLT2 inhibitors, for example empagliflozin or dapagliflozin

Before surgery: Stop 3 to 4 days before surgery (4 days for ertugliflozin) in US guidance, or omit the day before and the day of surgery in UK guidance. Your plan will state which
After surgery: Restart only when eating and drinking normally; after major surgery, not until ketones are normal

Long-acting (basal) insulin

Before surgery: Usually continued at a reduced dose, often about 75 to 80 percent, the night before or morning of surgery
After surgery: Continue, and adjust with your readings

Intermediate (NPH) or premixed insulin

Before surgery: Usually about half the usual morning dose
After surgery: Return to usual doses as eating resumes

Insulin pump

Before surgery: Often continued at the basal rate for short procedures, with an agreed plan. Never stop insulin completely
After surgery: Resume usual settings when eating

Medicine	Before surgery	After surgery
Metformin	Usually omitted on the day of surgery; longer if there are contrast dye or kidney concerns	Restart when eating and drinking, if kidney function is normal
Sulfonylureas, for example gliclazide	Omit on the day of surgery, because of low sugar risk while fasting	Restart when eating normally
DPP-4 inhibitors, for example sitagliptin	Often continued; follow your protocol	Continue when eating
SGLT2 inhibitors, for example empagliflozin or dapagliflozin	Stop 3 to 4 days before surgery (4 days for ertugliflozin) in US guidance, or omit the day before and the day of surgery in UK guidance. Your plan will state which	Restart only when eating and drinking normally; after major surgery, not until ketones are normal
Long-acting (basal) insulin	Usually continued at a reduced dose, often about 75 to 80 percent, the night before or morning of surgery	Continue, and adjust with your readings
Intermediate (NPH) or premixed insulin	Usually about half the usual morning dose	Return to usual doses as eating resumes
Insulin pump	Often continued at the basal rate for short procedures, with an agreed plan. Never stop insulin completely	Resume usual settings when eating

Low Blood Sugar: Recognize and Treat It

Low blood sugar (below about 70 mg/dL or 4 mmol/L) is most likely if you take insulin or sulfonylureas and are fasting. The signs are shaking, sweating, hunger, confusion, or unusual behaviour.

Take 15 to 20 g of fast-acting glucose: a small glass of juice or glucose tablets.
Check again after 15 minutes, and repeat if still low.
Once it has recovered, eat a snack or a meal.
Even while fasting before surgery, you may take a clear glucose drink within the fasting rules. Tell the staff when you arrive.

SGLT2 Tablets and a Hidden Danger: Ketoacidosis

SGLT2 inhibitors are also prescribed for heart failure and kidney disease, not only diabetes. During fasting, surgery, or illness they can cause a dangerous acid build-up in the blood (ketoacidosis) even when the blood sugar is normal, which makes it easy to miss. Nausea, vomiting, abdominal pain, fast breathing, or drowsiness in someone taking one of these tablets should always be checked with a blood ketone test, whatever the sugar level.

Recovery After Surgery With Diabetes

Your sugar will probably be higher for a few days; surgery and stress raise it. It is checked every 1 to 2 hours while you are fasting or in surgery, and before meals afterward.
Restart each medicine exactly as written in your plan.
Diabetes slows healing: protect your heels and feet from pressure in bed, and check your feet and wound daily.
If you become unwell and cannot eat or drink normally, contact the team the same day. Some medicines are paused while you are dehydrated; never guess which.

Ramadan and Diabetes Surgery

Planned surgery is best scheduled outside Ramadan for people with diabetes, where possible.
Do not fast until you have recovered, are eating normally, and your sugar is stable.
Fasting on an SGLT2 inhibitor carries a higher risk of dehydration and ketoacidosis, and insulin or sulfonylurea doses usually need changing for fasting. If you wish to fast after recovery, make an individual plan with your diabetes team first.

Warning Signs: When to Seek Help

Green

What you notice: Sugar a little higher than usual for a few days after surgery
What to do: Expected. Keep checking and follow your plan

Amber

What you notice: Sugar above about 250 mg/dL (14 mmol/L) on two checks; sugar often below 70 mg/dL (4 mmol/L); a wound that is red, warm, or leaking
What to do: Call the clinic or diabetes team the same day

Red

What you notice: Vomiting, abdominal pain, fast breathing, or drowsiness, especially if you take an SGLT2 tablet, even with a normal sugar; raised blood ketones; low sugar that does not recover, or confusion
What to do: Go to the emergency department now. Say that you have diabetes and which tablets you take

Level	What you notice	What to do
Green	Sugar a little higher than usual for a few days after surgery	Expected. Keep checking and follow your plan
Amber	Sugar above about 250 mg/dL (14 mmol/L) on two checks; sugar often below 70 mg/dL (4 mmol/L); a wound that is red, warm, or leaking	Call the clinic or diabetes team the same day
Red	Vomiting, abdominal pain, fast breathing, or drowsiness, especially if you take an SGLT2 tablet, even with a normal sugar; raised blood ketones; low sugar that does not recover, or confusion	Go to the emergency department now. Say that you have diabetes and which tablets you take

Questions Patients Ask

Why do I need to stop my tablet days before the operation?

Some tablets, called SGLT2 inhibitors, can cause a dangerous acid build-up in the blood when you are fasting or unwell, even if your sugar looks normal. Stopping them before surgery prevents this.

Should I take my insulin on the morning of surgery?

Usually you take a reduced dose of your long-acting insulin, but not your mealtime insulin. Follow your written plan exactly.

Will diabetes slow my healing?

It can. Keeping your sugar in the target range, stopping smoking, and eating enough protein help your wound heal.

I have an insulin pump. Will I have to take it off?

For short operations, many people keep their pump on its basal rate with an agreed plan. For longer operations, the team may switch to an insulin drip. Insulin is never stopped completely.

Full guide written by Dr. Tamer Elalfy