When switching from an insulin pump to subcutaneous (SC) injection, should a 1-hour overlap be used?

Switching from Insulin Pump to Subcutaneous Injection: Overlap Timing

When transitioning from an insulin pump to subcutaneous basal insulin, you should administer the subcutaneous basal insulin injection 2 hours before disconnecting the pump, not 1 hour. This 2-hour overlap is critical to prevent dangerous rebound hyperglycemia and establish adequate subcutaneous insulin depot before pump discontinuation.

Critical Timing Requirements

The 2-hour overlap is the evidence-based standard for pump-to-subcutaneous transitions:

• The British Journal of Anaesthesia explicitly recommends that when restarting a pump after IV insulin, the pump should infuse at basal rate for at least 2 hours before stopping IV insulin to establish adequate subcutaneous insulin depot 1
• The American Diabetes Association recommends administering subcutaneous basal insulin 2 hours before discontinuing IV insulin infusion to prevent rebound hyperglycemia 2
• When discontinuing a pump for subcutaneous basal-bolus therapy, the pump should be stopped 2 hours after the first injection of long-acting basal insulin (glargine or detemir) 1

Why 2 Hours, Not 1 Hour?

The pharmacokinetic rationale is clear:

• Patients become relatively insulin deficient within one hour of pump disconnection, making a 1-hour overlap insufficient 1
• Long-acting insulin analogs (glargine, detemir) require approximately 2 hours to establish therapeutic subcutaneous depot levels 1
• A 1-hour overlap creates a dangerous gap in insulin coverage, risking hyperglycemia and potential ketosis in Type 1 diabetes patients 1

Dosing Strategy for Transition

Calculate the replacement dose based on the pump's 24-hour basal insulin:

• Use the total 24-hour basal dose from the pump menu and divide it into 2 equal doses of long-acting insulin given 12 hours apart 1
• For example, if total daily basal dose is 22 units, give 11 units of glargine or detemir every 12 hours 1
• Administer the first dose of basal insulin, wait 2 hours, then disconnect the pump 1

Prandial Insulin Management

Add rapid-acting insulin for meals:

• Continue using the patient's established insulin-to-carbohydrate ratios and correction factors from their pump settings 1
• Give rapid-acting insulin (lispro, aspart) before each meal based on carbohydrate content 1

Monitoring Requirements

Intensive glucose monitoring is mandatory during transition:

• Check blood glucose 2 hours after the basal insulin injection to ensure adequate coverage 1
• Continue hourly glucose monitoring during the transition period 1
• Monitor for hyperglycemia (>250 mg/dL) and check for ketones if glucose exceeds 300 mg/dL 1

Common Pitfalls to Avoid

Critical errors that lead to poor outcomes:

• Never disconnect the pump before giving basal insulin - this creates immediate insulin deficiency and rapid hyperglycemia 1
• Never use only a 1-hour overlap - insufficient time for subcutaneous depot formation 1
• Never delay starting IV insulin if pump must be removed emergently - begin IV insulin immediately and simultaneously with pump disconnection in emergency situations 1

Special Circumstances

When immediate pump discontinuation is required:

• In emergencies (DKA, surgery, patient unable to manage pump), start IV insulin at least 30 minutes before pump removal when possible 1
• If the patient is postoperative and autonomous, reconnect the pump as soon as they can self-manage 1
• If the patient cannot self-manage postoperatively, initiate basal-bolus subcutaneous insulin immediately with the 2-hour overlap protocol 1