Blood Sugar Control Around Surgery

If you have diabetes and an operation has been scheduled — a gall bladder, a hernia, a knee replacement, a C-section, a dental extraction under anaesthesia — the surgery you are being offered is the same surgery everyone else is offered. Nothing about diabetes makes it a different operation.

What diabetes changes is the scaffolding around it. Three things in particular: what gets checked in the weeks beforehand, what happens to your medicines during the hours you are not allowed to eat, and how long your readings stay unsettled once it is over. None of these are complicated. They just have to be decided by someone, in advance, and written down — and that is where they most often get missed.

Why anyone bothers: it is the glucose, not the label

The reason surgical teams pay attention to diabetes is that high glucose interferes with the specific things a body has to do after being operated on — send white cells to a wound, lay down new tissue, close a surgical site cleanly. The 2026 consensus statement from the Association of Anaesthetists and the Joint British Diabetes Societies (opens in a new tab) lists what the observational data link diabetes to after surgery: longer hospital stays, surgical site infections, chest and urinary infections, and a higher chance of needing intensive care.

That list reads alarmingly until you see where the risk actually sits. A study of 790 orthopaedic trauma patients (opens in a new tab) is unusually clarifying here, because everyone in it had no known diabetes — people with a diagnosis were deliberately excluded. Among those whose glucose ran at or above 200 mg/dL on two or more readings after surgery, the wound infection rate was 4.4% against 1.6% in the rest; adjusted for other factors, that is 2.7 times the odds. At a sustained level at or above 140 mg/dL, infection ran 7.5% against 1.7%.

In other words: it was the raised sugar that mattered, in people who did not have diabetes at all. Which is genuinely good news if you do, because glucose is the one variable in that whole list you and your team can actually move — and the weeks before a planned operation are exactly when there is time to move it.

The pre-operative HbA1c, and what it is really for

Most surgical teams will want a recent HbA1c before a planned operation. It is not a pass mark. It is a way of asking whether the weeks around the surgery are likely to go smoothly, or whether a few months of steadier control first would make the whole thing safer.

The British consensus statement puts a number to the point where that conversation should happen: above 69 mmol/mol — roughly 8.5% on the scale used by most Pakistani labs — the guidance is to use clinical judgement about whether to proceed or refer back to your diabetes doctor first. Note the phrasing. Not "cancel", not "refuse". Judgement, weighed against how urgent the operation is.

Fasting is the part that actually trips people up

The nil-by-mouth window before anaesthesia is where diabetes and surgical routine collide. You are told not to eat. You may be taking medicines whose entire job is to lower blood sugar. And hospital lists slip — the 8 a.m. slot becomes a 2 p.m. slot, and a six-hour fast quietly becomes twelve.

This is why the consensus statement asks specifically that surgical scheduling be arranged to minimise fasting time for people with diabetes. In practice that usually means being placed early on the operating list. It is a reasonable thing to ask for by name at your pre-operative appointment, and it is much easier to arrange a week ahead than on the day.

The other half of the fast is knowing what to do if your sugar drops while you are waiting. You cannot eat — but hypoglycaemia still has to be treated, and the ward has glucose gel and intravenous options for exactly this. Tell the nurse the moment you feel it rather than waiting it out, and carry your own glucometer so you can check rather than guess.

Which medicines change, and when

This is the single most useful thing to leave your pre-operative appointment with in writing. The table below is what published guidance generally says — the American Diabetes Association's Standards of Care for diabetes in the hospital (opens in a new tab) for the timings, the British consensus for the monitoring — but the actual instruction has to come from your own team, because it depends on your operation, your kidney function and your exact doses.

What the team is aiming for on the day

The targets used around surgery are deliberately looser than your everyday ones, and it helps to know that in advance so a reading of 160 mg/dL on the ward does not feel like a failure.

• Within about four hours of surgery, the ADA's stated perioperative target is 100–180 mg/dL (5.6–10.0 mmol/L).
• During a hospital stay generally, the target for most patients is 140–180 mg/dL (7.8–10.0 mmol/L).
• The British consensus frames it slightly differently: 6–10 mmol/L (roughly 108–180 mg/dL) for people on insulin, sulfonylureas or meglitinides, and 4–10 mmol/L (roughly 72–180 mg/dL) for diabetes managed by diet or other tablets — the higher floor for the first group being deliberate protection against a hypo.

The wider range is not carelessness. In a fasting, stressed, sedated person who cannot tell you they feel shaky, a hypoglycaemic episode is both more dangerous and harder to spot than a reading that sits a little high for a day. If your readings are handled with an insulin drip — a variable rate infusion — expect hourly finger-prick checks; the consensus statement reserves that approach for when you are metabolically unsettled or will miss more than one meal.

Afterwards: why your readings stop making sense for a while

Almost everyone is surprised by this. You have eaten less than usual, and your sugar is higher than usual, and it feels like the numbers have turned on you.

They have not. Surgery is a physical stress, and the body's stress hormones raise blood glucose on purpose. Pain does the same. The steroids often given during anaesthesia to prevent nausea push it up further. You are moving far less than normal, which removes a quiet part of your daily glucose disposal. And the medicines that usually hold your numbers down are, by design, partly paused. High readings for several days after an operation are an expected feature of recovery, not evidence that your diabetes has suddenly worsened.

What matters in that period is the restarting, and the restarting is what tends to be forgotten in a discharge rush:

1. 1Get the restart instructions in writing before you leave, medicine by medicine — including which ones are still on hold and what has to be true before they resume. "When you are eating and drinking normally" is the usual condition; make sure you know which day that points to for each one.
2. 2Check more often than usual for the first week or two. Readings are genuinely more variable now, and the only way to know whether the pattern is settling is to have the pattern written down.
3. 3If you take an SGLT2 inhibitor, keep checking ketones daily until you are back to eating and drinking properly — normal glucose readings do not rule this one out.
4. 4Watch the wound the way you would watch a foot. Spreading redness, increasing rather than settling pain, heat, discharge or a fever all need to be seen, and they need to be seen early rather than at the scheduled follow-up.

Emergency surgery, where there is no runway

Everything above assumes a planned operation with weeks of notice. An appendix, an obstructed hernia or a road accident gives you none of that, and the team will simply manage your glucose as they go — often with an insulin infusion rather than your usual regimen.

The one thing you or the person with you can do is make sure the diabetes is known immediately, along with the actual names and doses of the medicines — not "a sugar tablet in the morning". This is the strongest practical argument for keeping a current medicine list on your phone, where anyone accompanying you to a casualty department can read it out.

A few practical notes for hospitals in Pakistan

• Take your own glucometer and enough strips. Ward checks happen on the ward's schedule, and having your own meter is what lets you check when something feels off — particularly during a long wait before your slot.
• Take your own insulin in a cool bag, and tell the staff you have it, rather than using it unannounced. Supply and brand availability vary between hospitals, and continuity of the exact insulin you are used to is worth protecting.
• Make sure the anaesthetist, not only the surgeon, knows about the diabetes. The medicine decisions around the fast are largely theirs. If your surgery is being done in a smaller setup or a camp, ask directly who is making them.
• Bring the HbA1c and kidney function reports with you. Records do not always travel between a lab, a clinic and a hospital in Pakistan, and a missing creatinine value is a common reason for a last-minute delay.

None of this requires you to manage your own surgery. It requires you to arrive with your numbers, your medicine list and a small set of questions — which is a far more ordinary task than it sounds, and it is most of what separates a straightforward recovery from a complicated one.

Keep your surgery plan where you can actually find it

Log your readings, your medicine list and the dates each paused medicine is meant to restart in Diatic — so the pre-operative appointment, the fasting day and the weeks of recovery are all working from the same record rather than from memory.

Start logging with Diatic (opens Diatic on Google Play in a new tab)