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Intrauterine Growth Restriction Ameliorates the Effects of Gradual Hemorrhagic Hypotension on Regional Cerebral Blood Flow and Brain Oxygen Uptake in Newborn Piglets

Data are scant regarding the development of cerebrovascular autoregulation in intrauterine growth-restricted (IUGR) newborns. We tested the hypothesis that IUGR improves the ability of neonates to withstand critical periods of gradual hemorrhagic hypotension by optimizing cerebrovascular autoregulation. Studies were conducted on 1-d-old anesthetized piglets divided into groups of normal weight (NW, n = 14, body weight = 1518 ± 122 g) and IUGR (n = 14, body weight = 829 ± 50 g) animals. Physiologic parameters, including regional cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2), were similar in NW and IUGR piglets under baseline conditions. Controlled arterial blood loss [hemorrhagic hypotension (HH)] induced a stepwise reduction of the mean arterial blood pressure of 49 ± 3 mm Hg (mild HH), 39 ± 3 mm Hg (moderate HH), and 30 ± 3 mm Hg (severe HH) in seven NW and seven IUGR piglets (p < 0.05). In NW piglets, cortical CBF and CMRO2 was reduced already at moderate HH (p < 0.05). A similar CMRO2 reduction occurred during severe HH in NW and IUGR piglets (p < 0.05). In addition, during mild and moderate HH, primarily in IUGR piglets, an increase in regional CBF of brainstem, cerebellum, and thalamus was shown compared with baseline values (p < 0.05). Furthermore, under these conditions, cerebral cortex blood flow was maintained in newborn IUGR animals. In contrast, NW piglets exhibited a significant reduction in CBF (p < 0.05) during moderate HH. Thus, IUGR resulted in an improved ability to withstand critical periods of gradual oxygen deficit as shown by improved cerebrovascular autoregulation during hemorrhagic hypotension.