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

Abstract

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 (SpO₂), mean arterial blood pressure (MABP), and cerebral saturation (near-infrared spectroscopy, SctO₂) 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.

Figure 1

Histogram of MABP values record in the two groups. The less mature group is shown with black bars, the more mature group with white bars. Overlap between groups is shown in gray.

Figure 2

Blood pressure vs. FTOE is shown for both groups (solid line - 23–25 weeks, dashed line - 26–28 weeks). Blood pressure group is defined by color with low MABP in red, medium in blue, and high in green. Note the increase in FTOE during hypotension for the more mature infants, suggestive of a metabolically-driven autoregulatory response. In contrast, the more preterm group has a paradoxical drop in FTOE, suggesting immaturity of metabolically driven autoregulation. Whiskers represent ±1 SEM.

Figure 3

Blood pressure vs. FTOE by individual EGA groups. The more premature group is shown in blue (solid blue=23 weeks, dashed blue=24 weeks, dotted blue=25 weeks) and the more mature group shown in red (solid red=26 weeks, dashed red=27 weeks, dotted red=28 weeks). Whiskers represent ±1 SEM.