Can a patient with type 2 diabetes mellitus (T2DM) be placed on an insulin sliding scale after undergoing major surgery to achieve tighter control of blood glucose levels?

Sliding Scale Insulin After Major Surgery in Type 2 Diabetes

No, a patient with type 2 diabetes should NOT be placed on sliding scale insulin alone after major surgery, as this approach is associated with poor glycemic control and has been consistently shown to be inferior to basal-bolus insulin regimens. 1

Why Sliding Scale Insulin Fails

Sliding scale insulin (SSI) is widely condemned in clinical guidelines despite its continued use in some hospitals 1. The fundamental problem is that SSI is a "reactive" approach that treats hyperglycemia after it has already occurred, rather than preventing it 1. This leads to:

• Clinically significant hyperglycemia in the majority of patients 1
• Rapid fluctuations in blood glucose levels, exacerbating both hyper- and hypoglycemia 1
• The prescribed sliding scale typically remains unchanged throughout hospitalization even when control remains poor 1
• Higher rates of postoperative complications compared to basal-bolus regimens 1

The Superior Alternative: Basal-Bolus Insulin

For postoperative type 2 diabetes patients, a basal-bolus insulin regimen should be used instead, as randomized trials have consistently demonstrated better glycemic control and reduced complications. 1

Initial Dosing Strategy

For insulin-naive patients or those on low-dose insulin preoperatively:

• Start with 0.3-0.5 units/kg/day total daily dose 1
• Divide as 50% basal insulin (given once or twice daily) 1
• Divide as 50% rapid-acting insulin (split before three meals) 1
• Use lower doses (0.3 units/kg) for patients at higher hypoglycemia risk: age >65 years, renal failure, or poor oral intake 1

For patients on higher insulin doses at home (≥0.6 units/kg/day):

• Reduce total daily dose by 20% during hospitalization to prevent hypoglycemia 1

Evidence of Superiority

A landmark surgical trial demonstrated that basal-bolus insulin versus sliding scale alone resulted in 1:

• Lower composite complications rate: 9% versus 24% (p=0.003) including wound infection, pneumonia, bacteremia, acute renal and respiratory failure
• Better overall glycemic control
• The trade-off was higher hypoglycemia rates (23% vs 5%), though severe hypoglycemia (<40 mg/dL) remained low at 4%

Another study in obese hospitalized type 2 diabetes patients showed 1:

• 68% achieved mean blood glucose <140 mg/dL with basal-bolus versus only 38% with sliding scale alone
• No difference in hypoglycemia rates between groups

Basal-Plus: A Middle Ground Option

For patients with mild hyperglycemia (blood glucose <200 mg/dL), decreased oral intake, or those undergoing surgery, a basal-plus regimen may be preferred over full basal-bolus. 1

This consists of:

• Single daily basal insulin dose (0.1-0.25 units/kg/day) 1
• Correction doses of rapid-acting insulin before meals or every 6 hours if NPO 1
• Similar glycemic control to basal-bolus but with potentially lower hypoglycemia risk 1

Target Blood Glucose Ranges

Perioperative glycemic targets should be 1:

• 100-180 mg/dL (5.6-10.0 mmol/L) within 4 hours of surgery 1
• Tighter targets than 80-180 mg/dL do not improve outcomes and increase hypoglycemia risk 1

Monitoring Requirements

• Check blood glucose every 2-4 hours while NPO 1
• Monitor at least every 1-2 hours during the acute postoperative phase if on insulin therapy 2
• Increase monitoring frequency if on insulin or insulin secretagogues 2

Critical Pitfalls to Avoid

• Never use sliding scale insulin as monotherapy in patients with established insulin requirements 1
• Do not abruptly stop insulin once initiated, as this causes rebound hyperglycemia 2, 3
• Check for ketosis immediately in any diabetic patient with significant hyperglycemia to rule out ketoacidosis 2, 3
• Measure serum electrolytes urgently if blood glucose >300 mg/dL to assess for hyperosmolar state requiring ICU care 2, 3

When Sliding Scale May Be Acceptable

The only scenario where sliding scale insulin alone might be appropriate is in patients without diabetes who have mild stress hyperglycemia 1. However, it should absolutely not be used in type 1 diabetes 1.

Transition from IV to Subcutaneous Insulin

If the patient was on continuous IV insulin infusion postoperatively:

• Estimate subcutaneous requirements from the average insulin infused during the 12 hours before transition 1
• For example, 1.5 units/hour average = 36 units/24 hours total daily dose 1
• Give first subcutaneous basal insulin injection 1-2 hours before stopping IV infusion to ensure adequate overlap 3