Glucose monitoring with long-term subcutaneous microdialysis in neonates

Background. Microdialysis is a new approach for continuous monitoring of small molecules in the extracellular space, and hypoglycemia is a common problem in neonatal intensive care. The objective of this study was to evaluate subcutaneous microdialysis for long-term glucose monitoring in neonatal intensive care. We determined the relative recovery of the microdialysis system in vitro and in vivo, the stability of the relative recovery in vivo during long-term microdialysis, and the correlation between blood and dialysate concentrations of glucose and urea. Furthermore, we evaluated the sensitivity and specificy of subcutaneous microdialysis for the diagnosis of hypoglycemia. Patient and Methods. Thirteen infants (10 neonates) with gestational ages of 30.2 to 45.6 weeks were investigated by microdialysis of subcutaneous adipose tissue and blood sampling. Subcutaneous microdialysis was performed for a median (range) duration of 9 (4-16) days. Results. The application was safe, even in extremely low birth weight infants (< 1000 g) with scanty subcutaneous adipose tissue. The mean +/- standard deviation of the relative recovery in vitro was 101 +/- 3% for glucose and 100 +/- 2% for urea. Using urea as the internal standard, the mean relative recovery in vivo was 96.4 +/- 12.7% at the beginning and remained constant up to 16 days. The correlation between microdialysate and blood was significant for glucose (r = 0.88) and urea (r = 0.98). Subcutaneous microdialysis allowed the detection of asymptomatic hypoglycemias. The diagnostic sensitivity of a dialysate glucose 2.9 mM to predict a blood glucose level less than or equal to2.8 mM was 92.3%, with 88.1% specificy. The positive predictive value with a 13.4% prevalence of a blood glucose < 2.8 mM was 54.5%, with a negative predictive value of 98.7% and an accuracy of 88.7%. Conclusions. Subcutaneous microdialysis is a safe method, well suited for long-term glucose monitoring in neonates during intensive care. Subcutaneous microdialysis can be used to reduce blood loss and painful stress resulting from diagnostic blood sampling in high-risk neonates.