An insulin infusion is simply an intravenous form of basal insulin where the rate is adjusted according to the glucose level. Actrapid is infused via a syringe pump and glucose levels are monitored 1-hourly. A second intravenous line should run dextrose-containing fluids to prevent hypoglycemia.

While an insulin allows for flexibility in insulin dosing and is ideal in critical illness, the 1-hourly glucose monitoring is very demanding for patients and nursing staff. Infusions should be limited to 24 hours if possible.

When to use an insulin infusion

• Emergencies eg. DKA, HHS
• Sepsis
• Major surgery
• Severe hypoglycaemia
• Prolonged period of fasting
• Acute myocardial infarction and erratic glucose levels
• Betamethasone given to pregnant woman with insulin-treated diabetes
• Established labour in woman with type 1 diabetes or glucose level >8.0mmol/L
• Caesarean section for woman with insulin-treated diabetes

How to start an insulin infusion

Draw up Actrapid 50 units with 49.5ml of 0.18 Normal Saline in a 50ml syringe. This is loaded into a syringe driver that is set up at the initial infusion rate.

Establish a second intravenous line for dextrose-saline fluid, running at 125ml per hour.

If the patient usually takes basal insulin, give this at the usual dose and time. It is safe to give subcutaneous and intravenous insulin simultaneously. It means that when the infusion is ceased, there is a safe and easy transition back to subcutaneous insulin.

How to adjust an insulin infusion

When an insulin infusion is commenced, glucose levels should be monitored 1-hourly. Recheck the trend of glucose levels after 3 hours to ensure improving or stable glucose levels.

Adjust insulin infusion if glucose levels are not improving or if they are worsening. Change the infusion rate by 0.5 – 1 unit per hour for every glucose interval. Recheck trend of glucose levels again in 3-4 hours.

How to change to subcutaneous insulin

When an insulin infusion is ceased, circulating insulin levels fall within 15 minutes. If the subcutaneous insulin is not yet active, the gap in available insulin exposes the patient to hyperglycaemia and the potential for diabetic ketoacidosis (if patient has type 1 diabetes).

As soon as the decision is made to cease the insulin infusion, give a dose of basal insulin. When the patient is due to eat, also give a dose of bolus or rapid-acting insulin and cease the infusion 2 hours afterwards. This means that when the infusion is switched off, the subcutaneous insulin is active. The overlap means that the glucose levels remain stable.