Intravenous Insulin Infusion

An intravenous insulin infusion delivers short-acting insulin at a titratable rate, giving fast onset, a half-life of about 5 minutes, and quick reversal. It is used for diabetic ketoacidosis, hyperosmolar hyperglycaemic state, critical illness, major surgery and labour when subcutaneous insulin is unreliable. It must always be paired with a source of glucose, potassium and fluid.

Fixed rate versus variable rate. A fixed rate infusion (0.1 units/kg/hour in diabetic ketoacidosis and 0.05 units/kg/hour in hyperosmolar hyperglycaemic state) is used when ketones or osmolality must be cleared. A variable rate infusion is adjusted to glucose in critical illness and perioperative care.

Background insulin. In type 1 diabetes, continue the usual long-acting insulin alongside the infusion.

Insulin. Soluble human insulin, 50 units in 50 mL of 0.9% sodium chloride, giving 1 unit/mL, delivered by a syringe pump through a dedicated line.

Fluid. Give 5% or 10% glucose with potassium when the patient is not eating, in addition to or in place of sodium chloride as the clinical need dictates, with total fluid set by volume status.

Indications. Diabetic ketoacidosis, hyperosmolar state, critical illness with glucose over 10 mmol/L, perioperative care in type 1 diabetes with missed meals, poorly controlled diabetes before major surgery, labour in diabetes, and acute coronary syndromes with glucose over 10 mmol/L.

Variable rate scale (adults).

Target. 7.8 to 10 mmol/L in critically ill patients, and 6 to 10 mmol/L perioperatively.

Resistance. If glucose does not fall by at least 1 mmol/L in 2 hours, move to the next higher rate band.

Potassium. Add potassium chloride to fluids by serum potassium: none if over 5.5 mmol/L, 20 to 40 mmol/L of fluid if 3.5 to 5.5 mmol/L, and replace first if under 3.5 mmol/L.

Transition to subcutaneous insulin. - Restart the usual subcutaneous insulin when the patient eats. - Give the first subcutaneous rapid-acting dose with the meal and continue the infusion for 30 to 60 minutes afterwards. - Give long-acting insulin at least 2 hours before stopping the infusion, or give it throughout. - In patients not on insulin before, start with 80% of the 24-hour infusion total as the subcutaneous total daily dose, split as basal 50% and mealtime 50%.

Special groups. - Kidney impairment: insulin clearance falls; expect lower rates and watch for delayed hypoglycaemia. - Liver disease: lower rates and closer checks. - Pregnancy: used in labour with target 4 to 7 mmol/L. - Children: weight-based rates set by paediatric specialists.

Monitoring. Glucose hourly at the start and after each rate change, then every 2 hours when stable. Potassium, sodium and creatinine every 6 hours, and more often in ketoacidosis.

Safety. Use a dedicated line, a checked syringe label, and never stop the infusion without starting subcutaneous cover in type 1 diabetes. Never run the infusion without a glucose and potassium source.

Stopping. Stop when the patient is eating and drinking, glucose is stable at target for 4 hours, ketones are under 0.6 mmol/L, and subcutaneous insulin has been given.

Referral and escalation. Escalate for glucose under 4 mmol/L despite treatment, rising potassium or falling potassium, worsening acidosis, or failure of glucose to fall.