Objective We studied the effect of glycaemia on the cerebral tissue oxygenation index (TOI) and cerebral fractional tissue oxygen extraction (FTOE), as measured by near-infrared spectroscopy (NIRS).
Methods We continuously measured TOI (NIRO 300, Hamamatsu), glycaemia (Medtronic MiniMed CGMS System Gold), mean arterial blood pressure (MABP), saturation (SaO2) and when possible also tPCO2 for at least 4 h during the first week of life in neonates with gestational age <32 weeks and weight <1500 g. FTOE was calculated as (SaO2−TOI)/SaO2. The Spearman correlation was used to assess the correlations between glycaemia and TOI and FTOE. With partial correlation we corrected for saturation, MABP and tPCO2.
Results 61 measurements in 22 infants were analysed. In a subgroup of 24 measurements in 11 neonates tPCO2 was also continuously monitored. None of the patients suffered from severe hypo or hyperglycaemia. In the whole group we found a significant negative correlation (p = 0.0002) between glycaemia and TOI, also after correction for MABP, saturation and tPCO2 (p = 0.0046). In addition, we found a significant positive correlation between glycaemia and FTOE (p = 0.0055), which remained significant after additional correction for MABP and tPCO2 (p = 0.01).
Conclusion Our results indicate that in neonates during the first days of life glycaemia influences the cerebral oxygenation—even within the normal ranges and after correction for MABP, SaO2 and tPCO2, via changes in the cerebral blood flow.