How is a Variable Rate Intravenous Insulin Infusion (VRIII) prescribed pre-operatively for a type 2 diabetic patient?

Pre-operative Variable Rate Intravenous Insulin Infusion (VRIII) Protocol for Type 2 Diabetic Patients

For type 2 diabetic patients undergoing surgery, a Variable Rate Intravenous Insulin Infusion (VRIII) should be prescribed pre-operatively with a target blood glucose range of 5-10 mmol/L (0.9-1.8 g/L), using ultra-rapid short-acting insulin analogues administered continuously via an electronic syringe pump, always in association with IV glucose (4 g/h) and appropriate electrolyte monitoring. 1

Pre-operative Assessment

1. Glycemic Control Evaluation:

   • Measure HbA1c and recent capillary blood glucose levels 1
   • Target pre-operative blood glucose: <1.80 g/L (10 mmol/L) 1
   • Schedule diabetic patients early in the morning to minimize fasting time 1

2. Medication Management:

   • Hold non-insulin medications on the morning of surgery (except metformin, which should be stopped the evening before) 1
   • Continue usual insulin doses the evening before surgery 1
   • For patients on insulin pumps, maintain until arrival in surgical unit 1
   • Hold metformin on the day of surgery 1
   • Discontinue SGLT2 inhibitors 3-4 days before surgery 1

VRIII Prescription Protocol

1. Insulin Preparation:

   • Use only ultra-rapid short-acting insulin analogues 1
   • Dilute to a concentration of 1 IU/mL 1

2. Concurrent IV Glucose Administration:

   • Always administer with IV glucose (100-150 g/day, equivalent to 4 g/h) 1
   • Example: 10% glucose solution at 40 mL/h 1
   • Monitor for hypokalaemia induced by insulin 1

3. Initial Dosing Based on Blood Glucose:

   • For blood glucose <5 mmol/L: Stop insulin, administer 30% glucose (6g), inform clinician 1
   • For blood glucose 5-7 mmol/L: 0.5 IU/h 1
   • For blood glucose 7-9 mmol/L: 1 IU/h 1
   • For blood glucose 9-11 mmol/L: 1.5 IU/h 1
   • For blood glucose 11-14 mmol/L: 2 IU/h 1
   • For blood glucose 14-17 mmol/L: 3 IU/h + 4 IU bolus 1
   • For blood glucose >17 mmol/L: 4 IU/h + 6 IU bolus, inform clinician 1

4. Monitoring Requirements:

   • Measure blood glucose every 1-2 hours while on VRIII 1
   • Check blood glucose every hour after each change in insulin infusion rate 1
   • Check blood glucose every 15-30 minutes if hypoglycemia occurs 1
   • Monitor potassium every 4 hours (target: 4-4.5 mmol/L) 1
   • Prefer arterial or venous blood samples over capillary measurements 1

Adjusting VRIII Rates

1. For Hypoglycemia (Blood Glucose <4 mmol/L):

   • Stop insulin infusion immediately 1
   • Administer 2 ampoules (6g) of 30% glucose 1
   • Inform clinician 1
   • Recheck blood glucose after 15 minutes 1
   • Resume at half the previous rate when glucose >5 mmol/L 1

2. For Hyperglycemia:

   • Adjust insulin rate according to the protocol table 1
   • For persistent hyperglycemia >16.5 mmol/L (3 g/L), investigate for ketosis 1

Special Considerations

1. For Patients with Poor Glycemic Control:

   • A1C goal for elective surgeries should be <8% whenever possible 1
   • Patients with initial glucose >300 mg/dL may be difficult to control during surgery 2

2. Rescue Medication:

   • Always prescribe hypoglycemia rescue medication 3
   • Have 30% glucose solution readily available 1

3. Pitfalls to Avoid:

   • Do not aim for normoglycemia (0.80-1.20 g/L), as this increases risk of severe hypoglycemia 1
   • Do not rely solely on capillary blood glucose measurements, which can overestimate values during vasoconstriction 1
   • Avoid prolonged fasting periods; excess fasting averaged 12:20 hours in audit studies 4
   • Do not use VRIII without appropriate substrate fluids (5% glucose in 0.45% saline) 4

4. Transition Planning:

   • Plan for transition from VRIII to subcutaneous insulin post-operatively 1
   • Prepare for basal-bolus insulin regimen post-operatively 1

By following this protocol, you can effectively manage blood glucose levels in type 2 diabetic patients during the pre-operative period, minimizing the risks of both hyperglycemia and hypoglycemia while optimizing patient outcomes.