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People with diabetes should be seen several weeks before surgery for an assessment of glycaemic control and anaesthetic suitability, including their CVD risks and any treatment modifications instituted and stabilised before proceeding to surgery. Attaining glycaemic control (ie an HbA1c approaching 53 mmol/mol or 7%) in the preoperative period has been shown to result in fewer complications and shorter hospital stays after surgery.169 A patient with a HbA1c of >75 mmol/mol (>9%) may need to have their surgery delayed until glycaemic management is optimised.
Preoperative care is the same for minor and major surgery, but blood glucose levels should be monitored intra-operatively (a prolonged procedure) and postoperatively for several days. Insulin may be required postoperatively for some people with type 2 diabetes.
Appropriate written instructions should be given to the patient beforehand.
Patients who are prescribed oral glucose-lowering medications (eg metformin, sulphonylureas, acarbose, glitazones, SGLT2i, DPP-4i) as well as injectable GLP-1 RA such as exenatide:
- can continue their diabetes medications on the day prior to surgery – be aware that gastric emptying is affected by GLP-1 agonists
- on the advice of their anaesthetic team, may omit their oral glycaemic medications on the morning of surgery, irrespective of whether they are on the morning or afternoon list. Insulin requires individualised advice and is usually not completely omitted. Proactively seek specialist endocrinology and anaesthetic advice before planned procedures
- 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
Metformin can generally be recommenced 24 hours after major surgery provided that there has been no deterioration in serum creatinine.169 For patients pre-operatively and post-operatively using metformin and SGLT2 inhibitors, maintenance of hydration is important.
Patients with diabetes who are treated with insulin will usually require peri-operative insulin and glucose infusions, and close blood glucose monitoring. Many hospitals have a protocol or working plan that should be followed for the individual patient in that service.
For colonoscopy preparation,263 colonlytely or glycoprep rather than fleet or phosphoprep should be used in patients with renal impairment who may become severely hyperphosphataemic with phosphate preparations. Modifications of diet advised for colonoscopy preparation may alter glucose management and hypoglycaemic risks, so instruction on appropriate SMBG testing may be required.