What considerations are important for the care of patients with severe diabetes mellitus (DM) who require anesthesia?

Perioperative Management of Patients with Severe Diabetes Requiring Anesthesia

For patients with severe diabetes requiring anesthesia, elective surgery should be postponed if HbA1c is >8% or blood glucose is >16.5 mmol/L (297 mg/dL) on the day of surgery, with referral to a diabetologist for optimization; however, emergency surgery should proceed regardless of glucose control with intensive intraoperative insulin protocols targeting blood glucose of 5.6-10.0 mmol/L (100-180 mg/dL). 1, 2

Preoperative Assessment and Risk Stratification

Glycemic Control Evaluation

• Obtain a recent HbA1c measurement for all diabetic patients, as this is essential for determining perioperative risk and should guide clearance decisions 2
• Target HbA1c should be <8% (63.9 mmol/L) for elective surgeries whenever possible 1
• If HbA1c is between 6-8%, this indicates adequate control and the patient can be cleared for anesthesia with standard perioperative glucose monitoring 2
• For HbA1c >8% in non-urgent procedures, postpone surgery and refer to a diabetologist for optimization 2
• If blood glucose is >16.5 mmol/L (297 mg/dL) on the day of surgery, postpone elective procedures, administer corrective insulin bolus, and refer to diabetologist 1, 2

Cardiovascular and Autonomic Assessment

• Perform preoperative risk assessment for ischemic heart disease in patients at high risk, particularly those with autonomic neuropathy or renal failure 1
• Screen for silent myocardial ischemia through ECG, as this is present in 30-50% of type 2 diabetes patients, and consider stress testing if major surgery with Lee score ≥2 3
• Evaluate for cardiac autonomic neuropathy through orthostatic blood pressure changes and heart rate variability, as this increases sudden death risk 1, 3

Additional Complications Screening

• Assess for gastroparesis by questioning about abdominal pain, bloating, and vomiting, as this creates aspiration risk requiring rapid sequence induction 3
• Evaluate for difficult intubation using the palm print test, as long-term diabetes causes densification of periarticular collagen structures affecting temporomandibular and atlanto-occipital joints 1
• Measure glomerular filtration rate preoperatively, as diabetic nephropathy increases acute renal failure risk 3
• Screen for recent hypoglycemic episodes (blood glucose <3.9 mmol/L) in the last week, as these predict perioperative risk 3

Medication Management

Oral Hypoglycemic Agents

• Hold metformin on the day of surgery due to lactic acidosis risk, particularly in patients with renal failure (creatinine clearance <60 mL/min), severe heart failure, or those receiving iodinated contrast agents 1
• Do not restart metformin before 48 hours for major surgery and only after assuring adequate renal function 1
• Discontinue SGLT2 inhibitors 3-4 days before surgery to prevent euglycemic diabetic ketoacidosis 1
• Hold all other oral glucose-lowering agents the morning of surgery or procedure 1

Insulin Management

• Give half of NPH dose or 75-80% doses of long-acting analog insulin on the morning of surgery based on the type of diabetes and clinical judgment 1
• For insulin pump users, understand the "total basal delivery" preoperatively to allow prescription of long-acting insulin if the pump must be stopped 1
• For ambulatory or short-duration surgery, retain the insulin pump to continue basal delivery, with correction of hyperglycemia using subcutaneous ultra-rapid analog boluses 1
• The main risk with insulin pumps is ketoacidosis if continuation of insulin is not immediate after stopping the pump, requiring either subcutaneous basal-bolus or continuous intravenous insulin 1

Intraoperative Management

Blood Glucose Targets and Monitoring

• Target blood glucose range of 100-180 mg/dL (5.6-10.0 mmol/L) within 4 hours of surgery 1
• Monitor blood glucose at least every 2-4 hours while the patient takes nothing by mouth 1
• For lengthy surgeries, monitor capillary blood glucose hourly during the procedure 2
• Perioperative hyperglycemia >180 mg/dL (10 mmol/L) increases morbidity and mortality, particularly from infection 3
• Hyperglycemia >250 mg/dL (13.9 mmol/L) carries significantly higher complication risk 3, 4

Insulin Administration

• Use continuous IV insulin infusion via electronic syringe for patients requiring insulin or experiencing stress hyperglycemia 3
• Administer short- or rapid-acting insulin as needed for blood glucose control 1
• If blood glucose exceeds 10 mmol/L (180 mg/dL), administer ultra-rapid analogue insulin bolus 2
• In noncardiac general surgery patients, basal insulin plus premeal short- or rapid-acting insulin (basal-bolus) coverage is associated with improved glycemic outcomes and lower rates of perioperative complications compared with correction-only insulin 1
• Poor intraoperative glycemic control (defined as four consecutive blood glucose concentrations >200 mg/dL despite insulin therapy) is associated with a 7.2-fold increased odds of severe postoperative morbidity 5

Glucose Infusion

• Set up glucose infusion (starting from 7:00 AM) if the patient needs to fast while treated with insulin 1
• Stop glucose infusion if blood glucose exceeds 16.5 mmol/L (297 mg/dL) 1
• Patients taking sulfonylureas or glinides before emergency surgery also require glucose infusion if remaining fasted 1

Anesthetic Considerations

• No specific anesthetic agent has been proven superior for diabetic patients 1
• Prioritize regional anesthesia when possible for superior postoperative pain control and reduced insulin resistance 3
• Regional anesthesia is not contraindicated but requires careful preoperative documentation of pre-existing polyneuropathy and dysautonomia 1
• Both intravenous and perineural dexamethasone administration is associated with increased blood glucose levels, requiring consideration of risk-benefit ratio 6

Postoperative Management

Immediate Recovery Period

• Continue hourly capillary blood glucose monitoring until the patient is fully conscious and capable of self-management 3
• Maintain glucose infusion (10% dextrose at 40 mL/h) for insulin-dependent patients to prevent recurrent hypoglycemia 3
• Resume oral feeding as soon as possible postoperatively 2
• Continue regular blood glucose monitoring postoperatively 2

Insulin Resumption

• Resume insulin pump basal infusion once the patient can manage their device and is eating 3
• Start bolus insulin dosing with first postoperative carbohydrate ingestion 3
• Evidence indicates that reducing insulin given the evening before surgery by 25% (compared with usual dosing) is more likely to achieve perioperative blood glucose levels in target range with lower hypoglycemia risk 1

Hypoglycemia Management

• Capillary glucose <3.3 mmol/L represents significant hypoglycemia requiring immediate treatment, regardless of clinical signs 7
• For patients with altered consciousness unable to swallow, administer IV glucose immediately 7
• After initial glucose administration, continue regular monitoring to ensure recovery and detect recurrence 7
• Be aware that 40% of type 1 diabetes and 10% of insulin-treated type 2 diabetes patients have hypoglycemia unawareness, requiring more vigilant monitoring 3

Critical Pitfalls to Avoid

• Do not aim for strict normoglycemia (tighter than 80-180 mg/dL), as perioperative glycemic targets tighter than this range do not improve outcomes and are associated with more hypoglycemia 1, 3
• Never stop insulin pumps without immediate IV insulin replacement in type 1 diabetes patients, as ketoacidosis develops within hours 3
• Do not use continuous glucose monitor (CGM) readings for intraoperative glucose management due to lag time and perfusion-dependent inaccuracy 3
• Avoid assuming drowsiness is solely due to post-surgical sedation—always check glucose in any post-surgical patient with altered mental status 7
• Do not delay glucose administration while waiting for additional symptoms to develop—hypoglycemia <3.3 mmol/L requires immediate treatment even without clinical signs 7

When to Consult Endocrinology

• Referral to a diabetologist is recommended for known diabetes with preoperative glycemic imbalance (HbA1c <5% or >8%), diabetes discovered during pre-anesthesia evaluation, blood glucose >16.5 mmol/L on day of surgery, or difficulty resuming previous treatment regimen 2