Perioperative Fasting Blood Glucose Target for Surgery
The recommended preoperative fasting blood glucose target for patients undergoing surgery is 100–180 mg/dL (5.6–10.0 mmol/L), with this same range maintained throughout the entire perioperative period. 1, 2, 3
Target Blood Glucose Range
Maintain blood glucose between 100–180 mg/dL (5.6–10.0 mmol/L) within 4 hours of surgery and throughout the perioperative period. 1, 2, 3
Do not pursue stricter glycemic targets below 100 mg/dL or tighter ranges (such as 80–180 mg/dL), as these do not improve surgical outcomes and significantly increase the risk of hypoglycemia without any mortality or morbidity benefit. 1, 2, 3
The broader target of 100–180 mg/dL (rather than normoglycemia of 80–120 mg/dL) represents the optimal balance between reducing hyperglycemia-related complications and avoiding dangerous hypoglycemic episodes. 1
Preoperative Optimization Context
For elective surgeries, the A1C should ideally be <8% (<64.0 mmol/L) whenever possible, as higher A1C levels increase surgical risk, mortality, and infection rates. 1, 2
However, the immediate preoperative fasting blood glucose target remains 100–180 mg/dL regardless of baseline A1C, as this is the range that reduces perioperative morbidity without increasing hypoglycemia risk. 1, 3
Monitoring Requirements
Check blood glucose at least every 2–4 hours while the patient is NPO (nothing by mouth) in the preoperative period. 1, 3
Use venous or arterial blood samples rather than capillary fingerstick measurements when possible, as capillary glucose readings can overestimate values, especially in the presence of vasoconstriction or hypoglycemia. 1
A capillary glucose reading of 70 mg/dL (3.8 mmol/L) should be treated as hypoglycemia and requires immediate correction with laboratory confirmation. 1
Insulin Adjustments to Achieve Target
Reduce basal insulin by 25% on the evening before surgery to achieve better perioperative glucose control with lower hypoglycemia risk compared to usual dosing. 2, 3, 4
On the morning of surgery, administer 75–80% of the usual long-acting basal insulin analog dose (such as glargine, detemir, or degludec) or 50% of the usual NPH insulin dose. 1, 2, 4
Hold all oral glucose-lowering agents on the morning of surgery, with metformin held on the day of surgery and SGLT2 inhibitors discontinued 3–4 days before surgery to prevent euglycemic diabetic ketoacidosis. 1, 2, 3
Administer short-acting or rapid-acting insulin as needed to maintain the 100–180 mg/dL target range while the patient is NPO. 1, 3
Critical Pitfalls to Avoid
Never pursue fasting glucose targets below 100 mg/dL perioperatively, as this dramatically increases hypoglycemia risk without improving surgical outcomes. 2, 3
Never use correction-only ("sliding scale") insulin without basal insulin coverage, as this approach is associated with worse glycemic outcomes and higher complication rates in surgical patients. 1, 2, 3
Never continue SGLT2 inhibitors within 3–4 days of surgery, as these medications pose a significant risk of life-threatening euglycemic diabetic ketoacidosis even when glucose levels appear normal. 2, 3
Special Considerations
Some protocols suggest a slightly narrower intraoperative target of 140–180 mg/dL, but the 100–180 mg/dL range is the most widely endorsed and safest target across the entire perioperative period. 5, 6
Patients with impaired fasting glucose (100–125 mg/dL) or undiagnosed diabetes are at increased risk for perioperative cardiovascular events, making glucose monitoring and control essential even in non-diabetic patients with elevated preoperative glucose. 7
The target of 100–180 mg/dL applies to both type 1 and type 2 diabetes, and to both elective and emergency surgical procedures. 1, 3