Cerebral Fractional Oxygen Extraction is Inversely Correlated with Oxygen Delivery in the Sick, Newborn, Preterm Infant

Abstract

Cerebral blood flow (CBF) is known to be low in newborn infants, but this has not been shown to be damaging. The purpose of this study was to investigate the relationships between cerebral haemoglobin flow, blood flow, oxygen delivery, oxygen consumption, venous saturation, and fractional oxygen extraction (OEF) in newborn, preterm infants. Measurements were made by nearinfrared spectroscopy in 13 very preterm, extremely low birth weight infants (median gestation 25 weeks) during the first 3 days after birth. There was a negative correlation between cerebral oxygen delivery and OEF (n ¼ 13, r ¼ À0.5, P ¼ 0.03), which implies that when there is a reduction in cerebral oxygen delivery in sick preterm infants, increased cerebral oxygen extraction may be responsible for maintaining oxygen availability to the brain. During the first 3 days after birth CBF (n ¼ 13, r ¼ 0.7, P ¼ 0.01), oxygen delivery (n ¼ 13, r ¼ 0.5, P ¼ 0.03), and oxygen consumption (n ¼ 13, r ¼ 0.7, P ¼ 0.004) all increased. This increase in oxygen consumption indicates increased cerebral metabolic activity after birth, which is likely to be a normal adaptation to extrauterine life. The increases in blood flow and oxygen delivery may also be normal adaptations that facilitate this increase in metabolic activity. There was a decrease (P ¼ 0.04) in mean (7s.d.) cerebral OEF between day 1 (0.3770.10) and day 2 (0.2970.09), with no change between day 2 and day 3. Taking into account the negative correlation between OEF and oxygen delivery, this decrease in OEF may be because of increased oxygen delivery during this time.

Definition of hypotension and assessment of hemodynamics in the preterm neonate

“…These preliminary findings suggest that patients developing a hemodynamically significant PDA have decreased rSO 2 , and thus diminished cerebral perfusion and oxygen delivery even a few hours after being born and that they compensate for the decrease in cerebral tissue oxygen delivery by increased oxygen extraction. 24 Similar findings have been reported recently. 36 …”

“…11 In fact, when the autoregulatory threshold is breached, it is likely that increases in cerebral fractional oxygen extraction, 23 microvascular dilation and a shift of the hemoglobin-oxygen dissociation curve to the left will maintain tissue oxygen delivery to a certain point. 24 If the blood pressure continues to fall past that point, cerebral function will become compromised ('functional blood pressure threshold', Figure 1). 11 The mean blood pressure value at which this occurs in the very preterm infant is unknown but may be near 24 mm Hg during the initial postnatal days.…”

“…11 The mean blood pressure value at which this occurs in the very preterm infant is unknown but may be near 24 mm Hg during the initial postnatal days. [23][24][25] Finally, if blood pressure continues to fall, structural integrity of the brain tissue will eventually be compromised ('ischemic blood pressure threshold', Figure 1). 11 In animal models, the ischemic blood pressure threshold is reached when the corresponding CBF is approximately 50% of the resting CBF.…”

In preterm infants, ascending intrauterine infection is associated with lower cerebral tissue oxygen saturation and higher oxygen extraction

“…A second possible explanation for lower r c SO 2 and higher FTOE was higher cerebral oxygen consumption. Higher cerebral oxygen consumption may reflect increased cerebral metabolic activity (17). We surmise that increased metabolic activity might be due to cytokine activation in the presence of AIUI.…”

“…The lower r c SO 2 and higher FTOE in the presence of AIUI may be either due to reduced cerebral oxygen supply or due to higher cerebral oxygen consumption (17). Firstly, the reduced cerebral oxygen supply might be the result of lower cerebral blood flow.…”