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

BACKGROUND: Premature infants may lack mature cerebrovascular autoregulatory function and fail to adapt oxygen extraction to decreasing systemic perfusion. METHODS: Infants ≤ 28 wks 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 72h. Resulting data underwent error processing. For each remaining 10m window, mean MABP and fractional tissue oxygen extraction (FTOE) were calculated. Infants were divided into two groups (23–25 wks and 26–28 wks). Median FTOE at low, medium and high MABP values (empirically defined within each group based on the 25(th) and 75(th) centile) were compared between EGA groups. RESULTS: Sample n=68, mean±SD GA=25.5±1.3 wks, BW=823±195g. 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) CONCLUSION: The more mature group (GA 26–28 wks) 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.