During a safety fast in an infant with hyperinsulinism, should enteral feeds be stopped and the intravenous dextrose infusion be continued at a reduced rate?

Safety Fast Protocol in Hyperinsulinism

Yes, during a safety fast in infants with hyperinsulinism, enteral feeds should be stopped while intravenous dextrose is continued at a reduced rate to assess the infant's ability to maintain euglycemia without nutritional support.

Rationale and Protocol

The safety fast is a diagnostic procedure used to confirm resolution of hyperinsulinism, particularly in cases of suspected transient disease 1. The guideline explicitly states that once an infant is weaned off diazoxide, "glucose should be monitored closely for at least 5 days and a safety fast for 15 to 18 hours should be completed to prove resolution of hyperinsulinism" 1.

Key Components of the Safety Fast:

Purpose of the Fast:

• The safety fast tests whether the infant can maintain blood glucose >70 mg/dL without enteral nutrition
• This confirms that hyperinsulinism has resolved and the infant no longer has pathologic insulin secretion
• It is performed after diazoxide has been discontinued in cases of suspected transient hyperinsulinism 1

IV Dextrose Management:

• IV dextrose should be reduced (not stopped entirely) during the fast to provide a safety net
• The goal is to challenge the infant's glucose homeostasis while maintaining a backup glucose source
• The maximum safe rate of dextrose administration without producing glycosuria is 0.5 g/kg/hour, with about 95% retention at 0.8 g/kg/hour 2

Feeding Status:

• All enteral feeds must be stopped during the safety fast period
• This includes both oral feeds and continuous enteral nutrition
• The fast typically lasts 15-18 hours 1

Clinical Context and Monitoring

When to Perform:

• After diazoxide has been discontinued in transient hyperinsulinism cases
• When glucose levels have been stable >70 mg/dL for at least 2-4 weeks 1
• Following at least 5 days of close glucose monitoring post-medication discontinuation 1

Safety Considerations:

• Fasting is safe when conducted on an experienced unit with appropriate guidelines 3
• Blood glucose should be monitored frequently during the fast
• The procedure should be stopped immediately if blood glucose falls below safe thresholds (typically <2.6-2.8 mmol/L or <50 mg/dL)
• Emergency dextrose bolus (10-25 grams or 20-50 mL of 50% dextrose) should be readily available 2

Common Pitfalls to Avoid

Do not:

• Continue full enteral feeds during the safety fast—this defeats the diagnostic purpose
• Stop IV dextrose completely without a safety protocol in place
• Perform the fast without experienced personnel and monitoring capabilities
• Attempt the fast before adequate stabilization off diazoxide

Critical distinction: The safety fast differs from routine hypoglycemia management. During active treatment of hyperinsulinism, continued enteral feeding alongside IV dextrose is actually beneficial and reduces duration of IV therapy 4. However, the safety fast is specifically designed to challenge the system by withdrawing enteral nutrition while maintaining reduced IV support.

The reduced-rate IV dextrose serves as a safety mechanism during this diagnostic challenge, allowing early intervention if the infant cannot maintain euglycemia, thereby preventing severe hypoglycemia and potential neurological sequelae.