What are the guidelines for controlling blood glucose (CBG) levels after heart surgery?

Blood Glucose Control After Heart Surgery

Use continuous intravenous insulin to maintain postoperative blood glucose ≤180 mg/dL (10.0 mmol/L) after cardiac surgery, avoiding targets below 140 mg/dL intraoperatively or below 110 mg/dL (6.1 mmol/L) postoperatively, as tighter control increases hypoglycemia risk without improving outcomes. 1

Postoperative Target Range and Method

The ACC/AHA provides a Class I recommendation (highest level) for maintaining early postoperative blood glucose concentration ≤180 mg/dL using continuous intravenous insulin to reduce adverse events including deep sternal wound infection after CABG. 1

• Target blood glucose between 100-180 mg/dL (5.6-10.0 mmol/L) throughout the postoperative period 2
• Initiate intravenous insulin infusion when blood glucose reaches 180 mg/dL (10.0 mmol/L), with a relative trigger at 150 mg/dL (8.3 mmol/L) 1
• Continue IV insulin infusion until the morning of the third postoperative day for optimal outcomes 1
• Monitor blood glucose every 1-2 hours while patient is NPO to detect hypoglycemia or hyperglycemia 3

Intraoperative Management

Extremely tight intraoperative glucose control (<140 mg/dL) has uncertain effectiveness and may cause harm. 1

• The ACC/AHA assigns Class IIb (uncertain effectiveness) to targeting intraoperative blood glucose <140 mg/dL 1
• A Mayo Clinic randomized trial found intensive intraoperative treatment caused increased death and stroke compared to conventional treatment 1
• Cleveland Clinic data from 4,300 cardiac surgery patients showed intraoperative glucose <140 mg/dL was not associated with improved outcomes compared to moderate hyperglycemia 1
• Intraoperative prevention of hyperglycemia with insulin may be considered (Class IIb recommendation) but is not strongly recommended 1

Critical Thresholds to Avoid

Postoperative targets <110 mg/dL (6.1 mmol/L) are explicitly not recommended (Class III: Harm). 1

• Targets below 110 mg/dL increase hypoglycemia risk 5- to 6-fold without reducing 90-day mortality 1
• Meta-analyses demonstrate no mortality reduction with intensive blood glucose control but significantly increased hypoglycemia 1
• Stricter glycemic targets (<100 mg/dL) increase hypoglycemia risk without improving outcomes 2

Evidence Behind the Recommendations

The Portland Diabetes Project demonstrated that continuous IV insulin maintaining glucose 120-160 mg/dL reduced deep sternal wound infection and cardiac-related deaths compared to higher targets 1. However, subsequent trials attempting even tighter control showed harm rather than benefit 1.

The European Society of Cardiology guidelines (2014) provide Class I, Level B evidence for postoperative hyperglycemia prevention targeting at least <180 mg/dL by IV insulin therapy in high-risk surgery patients requiring ICU admission 1. This represents the strongest consensus across multiple guideline bodies.

Transition from IV to Subcutaneous Insulin

• Maintain IV insulin until blood glucose stabilizes at ≤180 mg/dL and oral feeding resumes 3
• Transition when glucose has been stable for at least 24 hours and IV infusion rate is <3 U/h 3
• Administer long-acting (basal) insulin immediately after stopping IV insulin 3
• Calculate initial subcutaneous dose based on total daily IV insulin requirements: half as basal insulin, half as rapid-acting analogue 3
• For patients not previously on insulin with IV infusion <24 hours, start at 0.5-1 IU/kg (half basal, half rapid-acting) 3

Management of Glycemic Emergencies

For hypoglycemia (<60 mg/dL or 3.3 mmol/L), administer glucose immediately even without clinical signs. 3

• Use oral glucose if patient is conscious; IV glucose if unconscious or unable to swallow 3
• For glucose 70-100 mg/dL (3.8-5.5 mmol/L) with hypoglycemic symptoms, administer glucose 3
• For severe hyperglycemia (>300 mg/dL or 16.5 mmol/L), check for ketosis, ensure adequate hydration, and administer ultra-rapid insulin 3

Clinical Outcomes Associated with Poor Control

Recent prospective data (2024) shows that postoperative hyperglycemia ≥180 mg/dL occurs in 30% of cardiac surgery patients and is associated with: 4

• Higher rates of acute kidney injury (34.9% vs 18.9%) 4
• Longer mechanical ventilation duration (959 vs 720 minutes) 4
• Increased ICU-acquired weakness (14% vs 5.5%) 4
• Higher multiorgan failure rates (6.3% vs 0.7%) 4

Common Pitfalls to Avoid

• Do not attempt intraoperative glucose targets <140 mg/dL - this increases stroke and death risk without benefit 1, 2
• Do not target postoperative glucose <110 mg/dL - this is a Class III (Harm) recommendation due to severe hypoglycemia risk 1
• Do not use correction-only insulin without basal coverage in non-cardiac surgery patients 2
• Do not rely on subcutaneous insulin alone in the immediate postoperative period - continuous IV insulin is the preferred method for critically ill patients 2, 3
• Do not use continuous glucose monitoring (CGM) alone for glucose monitoring during surgery 2