Gestational age-dependent relationship between cerebral oxygen extraction and blood pressure

BackgroundPremature infants may lack mature cerebrovascular autoregulatory function and fail to adapt oxygen extraction to decreasing systemic perfusion.MethodsInfants ≤28 weeks of gestational age (GA) were recruited. Systemic oxygen saturation (SpO 2), mean arterial blood pressure (MABP), and cerebral saturation (near-infrared spectroscopy, SctO 2) were measured continuously over the first 72 h. Resulting data underwent error-processing. For each remaining 10 m window, the mean MABP and fractional tissue oxygen extraction (FTOE) were calculated. The infants were divided into two groups (23-25 and 26-28 weeks). The median FTOE at low, medium, and high MABP values (empirically defined within each group based on the 25th and 75th centile) were compared between estimated gestational age (EGA) groups.ResultsSample n=68, mean±SD GA=25.5±1.3 weeks, and birthweight (BW)=823±195 g. The median FTOE in the more preterm group vs. more mature group was statistically different at lower value of MABP (P<0.01) and higher values of MABP (P=0.01), but not at medium values (P=0.55).ConclusionThe more mature group (GA 26-28 weeks) displayed an appropriate increase in oxygen extraction during hypotension, steadily decreasing as MABP increased, suggesting mature autoregulation. An opposite response was noted in the more preterm group, suggesting an inability to mount a compensatory response when BP is outside of the physiologic range.