People with diabetes should be seen several weeks before surgery for an assessment of glycaemic control and anaesthetic suitability, including their cardiovascular disease risks, and any treatment modifications instituted and stabilised from the time of referral before proceeding to surgery.
Attaining glycaemic control (ie a glycated haemoglobin [HbA1c] approaching 7%, or 53 mmol/mol) in the pre-operative period has been shown to result in fewer complications and shorter hospital stays after surgery.5 A patient with an HbA1c of ≥9% (75 mmol/mol) may need to have their surgery delayed until glycaemic management is optimised.5
Pre-operative care is the same for minor and major surgery. For prolonged procedures, blood glucose levels should be monitored intra- and post-operatively for several days.
Insulin may be required post-operatively for some people with type 2 diabetes.
Further information can be found in the Australian Diabetes Society’s Peri-operative diabetes management guidelines.
Rural GPs who perform operations and GPs who administer anaesthetics should refer to these guidelines.
Ceasing medication before surgery
Appropriate written instructions should be given to the patient beforehand.
Patients who are prescribed oral glucose-lowering medications except SGLT2 inhibitors, and patients on injectable GLP-1 RAs:
- can continue their diabetes medications on the day prior to surgery (be aware that gastric emptying is affected by GLP-1 RAs)
- should omit their oral glucose-lowering medications on the morning of surgery, irrespective of whether they are on the morning or afternoon list.
SGLT2 inhibitors should be ceased at least three days prior to surgery and procedures that require one or more days in hospital and/or require bowel preparation, including endoscopy/colonoscopy (two days prior to and the day of the procedure), to prevent DKA in the peri-operative period.2 Other glucose-lowering medications may need to be increased in this period.2
For day procedures (including gastroscopy), SGLT2 inhibitors may be ceased just for the day of procedure. However, fasting before and after the procedure should be minimised.
Further advice on SGLT2 inhibitor use in the peri-operative period can be found in the Australian Diabetes Society’s alert regarding SGLT2 inhibitors and DKA risk during surgery.
Insulin requires individualised advice as follows, and is usually not completely omitted (never withhold basal insulin):
- Long-acting insulin – continue as usual (including morning doses)
- Short-acting insulin – omit rapid/short-acting insulin if not eating. Depending on timing of procedure
- morning: withhold short-acting insulin (and all oral glucose-lowering medication)
- afternoon: take half the normal morning rapid/short-acting dose in the morning before a light breakfast
- Premixed insulin – take one-third to half of the usual morning dose
People taking intermediate-acting insulin who are booked for afternoon procedures or on prolonged fasting may need a reduced dose. Seek specialist endocrinology and anaesthetic advice before planned procedures.
Patients on a multiple daily insulin regimen might require peri-operative glucose infusion and the associated close blood glucose monitoring. Many hospitals have a protocol or working plan that should be followed for the individual patient in that service.
Recommencing oral medication
Patients on oral glucose-lowering medication, with the exception of SGLT2 inhibitors, can generally recommence medications when they are able to eat meals. Specific advice is available in Australian Diabetes Society’s Peri-operative diabetes management guidelines.
SGLT2 inhibitors should only be recommenced post-operatively when the patient is eating and drinking normally or close to discharge from hospital. People who have had day surgery should only recommence SGLT2 inhibitors once they are on full oral intake. It may be prudent to delay recommencement for another 24 hours; however, this must be balanced against risk of hyperglycaemia.2
Metformin can generally be recommenced 24 hours after major surgery, provided there has been no deterioration in serum creatinine.5 For patients pre- and post-operatively using metformin and SGLT2 inhibitors, maintenance of hydration and carbohydrate intake is important.
Patients undergoing colonoscopy
For colonoscopy preparation, Colonlytely or Glycoprep, rather than Fleet or PhosphoPrep, should be used in patients with renal impairment, who may become severely hyperphosphataemic with phosphate preparations.6
The dietary modifications that are advised for colonoscopy preparation might alter glucose management and hypoglycaemic risks; instruction on appropriate SMBG testing may be required. It is also essential to avoid excessive carbohydrate restriction during the bowel preparation period if the patient has been using SGLT2 inhibitors.
On preparation days and day of procedure, commence SMBG and withhold all oral medications. Note that SGLT2 inhibitors should be ceased three days before colonoscopy and only recommenced when the patient is eating and drinking normally.2
Basal and/or rapid-acting insulin should be managed as above.
Premixed insulin should be managed as follows.
- On the day of bowel preparation, reduce premixed dose by half for all doses.
- On the day of procedure, arrange a morning procedure and use half usual dose and glucose infusion.