Patients with diabetes mellitus undergoing surgery are at increased risk of perioperative complications, including hypoglycaemia, hyperglycaemia, diabetic ketoacidosis, hyperosmolar hyperglycaemic state, wound infection, delayed wound healing, electrolyte disturbances, and cardiovascular events. Surgical stress induces the release of counter-regulatory hormones such as cortisol, catecholamines, glucagon, and growth hormone, resulting in increased insulin resistance and hepatic glucose production.

The goals of perioperative management are to maintain optimal glycaemic control, prevent acute metabolic complications, minimize infection risk, and promote normal wound healing while ensuring safe surgical outcomes.

Management should be individualized according to the type of diabetes, current treatment regimen, glycaemic control, and whether the planned procedure is minor or major.

Objectives

The objectives of perioperative diabetes management are to:

• Maintain blood glucose between 6 and 10 mmol/L during the perioperative period

• Prevent hypoglycaemia

• Prevent diabetic ketoacidosis and hyperosmolar hyperglycaemic state

• Reduce postoperative infections

• Promote wound healing

• Prevent electrolyte disturbances

• Reduce cardiovascular complications

• Resume the patient's usual diabetes treatment safely after surgery

Preoperative assessment

Every patient with diabetes scheduled for surgery should undergo a comprehensive preoperative evaluation.

Clinical assessment

The assessment should include:

• Type and duration of diabetes

• Current diabetes treatment

• Glycaemic control

• Previous hypoglycaemic episodes

• Previous diabetic ketoacidosis or hyperosmolar hyperglycaemic state

• History of cardiovascular disease

• Renal disease

• Liver disease

• Peripheral neuropathy

• Autonomic neuropathy

• Previous surgical complications

Physical examination

Assess:

• Blood pressure

• Weight

• Hydration status

• Cardiovascular system

• Respiratory system

• Foot examination

• Evidence of infection

Laboratory investigations

Recommended investigations include:

• Blood glucose

• HbA1c

• Serum creatinine

• Electrolytes

• Urinalysis

• Electrocardiogram (ECG), when indicated

Additional investigations should be performed according to the patient's clinical condition and the planned surgical procedure.

When surgery should be postponed

Whenever possible, elective surgery should be delayed if glycaemic control is poor.

Consider postponing surgery when:

• HbA1c is greater than 9%

• Fasting blood glucose is greater than 10 mmol/L

• Random blood glucose is greater than 13 mmol/L

Before surgery, patients should also be evaluated for:

• Diabetic nephropathy

• Cardiovascular disease

• Diabetic retinopathy

• Diabetic neuropathy

The surgical and anaesthetic teams should be informed of significant diabetes-related complications.

Minor surgery

Minor procedures include operations associated with short fasting periods and rapid return to oral intake.

Patients controlled with diet or oral hypoglycaemic agents

• Omit oral diabetes medications on the morning of surgery.

• Resume treatment once the patient is eating normally.

Patients with type 1 diabetes mellitus

• Continue the usual insulin regimen while avoiding prolonged fasting.

• Monitor blood glucose closely throughout the perioperative period.

Major surgery

Patients undergoing major surgery, prolonged fasting, or those with poor glycaemic control usually require intravenous insulin therapy.

Management includes:

• Continuous intravenous insulin infusion

• Intravenous fluids

• Regular blood glucose monitoring

• Electrolyte monitoring

The insulin infusion should usually begin before surgery and continue until the patient resumes adequate oral intake.

Target blood glucose:

6–10 mmol/L

Continuous intravenous insulin infusion

Continuous intravenous insulin infusion is recommended for:

• Major surgery

• Poor glycaemic control

• Patients already receiving insulin

• Emergency surgery

• Patients unable to eat for prolonged periods

The infusion is generally started in the morning of surgery and continued until the patient is able to eat normally.

Blood glucose should be monitored before surgery, during surgery, and after surgery.

Glucose-insulin-potassium regimen

Patients undergoing major surgery who are unable to eat should receive a glucose-insulin-potassium regimen to maintain glucose control and prevent ketosis.

Indications

The regimen should be started once oral intake is interrupted, regardless of the magnitude of the surgical procedure.

Its objectives are to:

• Prevent lipolysis

• Prevent ketogenesis

• Maintain glucose homeostasis

• Prevent diabetic ketoacidosis

• Maintain electrolyte balance

Standard regimen

Administer:

• 5% dextrose as maintenance intravenous fluid

In addition:

• Short-acting insulin 16 units

• Potassium chloride (KCl) 10 mmol

These are added to:

• 500 mL of 10% dextrose

Infusion rate:

80 mL/hour intravenously

Dose adjustment

Adjust the insulin dose according to the patient's clinical condition.

Patients with obesity or marked hyperglycaemia

If the initial blood glucose is greater than 14 mmol/L, consider increasing short-acting insulin to:

20 units

Patients who are very thin or normally require small insulin doses

Consider reducing short-acting insulin to:

12 units

Blood glucose monitoring during surgery

Blood glucose should be monitored:

• Before surgery

• Every hour during surgery

• Immediately after surgery

• Until glycaemic control is stable

The target blood glucose is:

6–10 mmol/L

Insulin dose adjustment during infusion

Adjust insulin according to hourly blood glucose measurements.

If blood glucose is:

Low or falling

Reduce insulin by:

4 units

High or rising

Increase insulin by:

4 units

Dose adjustments should always be accompanied by reassessment of fluid therapy and clinical status.

Management of patients receiving multiple daily insulin therapy

Patients receiving multiple daily insulin injections should continue their basal insulin throughout the perioperative period.

When oral intake is restricted:

• Administer regular short-acting insulin every 4–6 hours as required to control hyperglycaemia.

Once oral intake resumes:

• Restart the patient's usual basal-bolus insulin regimen.

Postoperative management

Following surgery:

Continue intravenous therapy using:

• 5–10% dextrose

• Potassium chloride 20 mmol

• Two-thirds of the patient's usual total daily insulin dose

This regimen should be infused over approximately 8 hours and repeated if necessary until the patient resumes oral feeding.

The intravenous insulin infusion should continue until approximately 60 minutes after the first meal.

Once oral intake is established:

• Resume the patient's usual diabetes treatment.

• Discontinue intravenous insulin when clinically appropriate.

Electrolyte monitoring

Electrolytes should be monitored daily during the perioperative period.

Particular attention should be paid to:

• Potassium

• Sodium

• Renal function

Electrolyte abnormalities should be corrected promptly.

Monitoring during the perioperative period

Regular assessment should include:

• Blood glucose

• Blood pressure

• Fluid balance

• Urine output

• Electrolytes

• Signs of infection

• Wound healing

• Level of consciousness

• Symptoms of hypoglycaemia

• Symptoms of hyperglycaemia

Prevention of perioperative complications

Complications can be minimized by:

• Optimizing glycaemic control before surgery

• Avoiding prolonged fasting

• Continuing appropriate insulin therapy

• Frequent blood glucose monitoring

• Maintaining adequate hydration

• Correcting electrolyte abnormalities

• Early mobilization

• Prompt treatment of infection

• Appropriate wound care

Complications

Potential perioperative complications include:

Metabolic complications

• Hypoglycaemia

• Hyperglycaemia

• Diabetic ketoacidosis

• Hyperosmolar hyperglycaemic state

Cardiovascular complications

• Myocardial infarction

• Cardiac arrhythmias

• Stroke

• Heart failure

Infectious complications

• Surgical site infection

• Sepsis

• Delayed wound healing

Renal complications

• Acute kidney injury

• Fluid and electrolyte imbalance

Patient education

Patients should receive counselling regarding:

• Medication adjustments before surgery

• Fasting instructions

• Blood glucose monitoring

• Recognition of hypoglycaemia

• Recognition of hyperglycaemia

• Postoperative medication resumption

• Wound care

• Follow-up appointments

Clinical pearls

• Elective surgery should ideally be postponed if HbA1c is greater than 9% or glycaemic control is poor.

• The recommended perioperative blood glucose target is 6–10 mmol/L.

• Oral hypoglycaemic agents are generally withheld on the morning of surgery and restarted once normal oral intake resumes.

• Patients with type 1 diabetes should never have basal insulin omitted, even during periods of fasting, to reduce the risk of diabetic ketoacidosis.

• Continuous intravenous insulin infusion is preferred for major surgery, emergency surgery, prolonged fasting, or poor glycaemic control.

• Hourly blood glucose monitoring and regular electrolyte assessment are essential during insulin infusion.

• Intravenous insulin should usually be continued until approximately 60 minutes after the first postoperative meal before transitioning back to the patient's usual diabetes regimen.