Case Report: Subcutaneous sensor-augmented insulin pump therapy in a 510-g preterm infant with hyperglycemia

Neonatal hyperglycemia affects up to 80% of extremely low birth weight (ELBW) infants and is independently associated with mortality, intraventricular hemorrhage, and adverse neurodevelopmental outcomes. Intravenous insulin infusion, which is the standard of care, requires dedicated vascular access. To the best of our knowledge, this is the first report of combined continuous glucose monitoring (CGM) and continuous subcutaneous insulin infusion (CSII) in an ELBW infant (birth weight <1,000 g). Transient hyperglycemia developed on day of life (DOL) 2, necessitating insulin therapy. A 55-min intravenous bridge facilitated the transition to a subcutaneous sensor-augmented pump system (Medtronic MiniMed 780G; Guardian 4 CGM sensor; insulin aspart, undiluted). Given a subcutaneous adipose tissue depth of approximately 1-2 mm, standard insertion devices were not applicable; tangential near-horizontal manual insertion by a physician achieved reliable subcutaneous positioning. Over 14 days, 3,931 CGM measurements were recorded; the mean glucose level was 162 ± 57 mg/dL (9.0 ± 3.2 mmol/L), and the time in the target range (62-180 mg/dL; 3.4-10.0 mmol/L) was 59.4%. CGM reduced the number of invasive reference glucose measurements from an estimated 84-168 to 20, representing a 76%-88% reduction in cutaneous punctures. Infusion set occlusion on DOL 6 was identified prospectively using CGM trend analysis. Combined CGM and CSII were maintained uninterrupted throughout laparotomy for focal intestinal perforation, allowing real-time perioperative glycemic surveillance and proactive insulin dose titration without additional invasive procedures. Insulin therapy was discontinued on DOL 17 as glucose levels normalized. This case establishes proof-of-concept for sensor-augmented subcutaneous insulin pump therapy at the physiological extreme of viability, providing a procedural foundation for neonatal-adapted closed-loop trials.