1. ¹Facultad de Medicina, Pontificia Universidad Catolica, Chile
2. ²Department of Physiology, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
3. ³Department of Obstetrics and Gynaecology, Faculty of Medicine and Health Sciences, University of Auckland, Auckland, New Zealand
4. ⁴Center for Perinatal Biology, Department of Physiology, Loma Linda University School of Medicine, Loma Linda, California, USA

Correspondence: Dr AJ Gunn, Department of Physiology, The University of Auckland, Private Bag 92019, Auckland, New Zealand. E-mail: aj.gunn@auckland.ac.nz

Received 7 October 2004; Revised 8 December 2004; Accepted 10 December 2004; Published online 23 February 2005.

Abstract

After exposure to asphyxia, infants may develop both prolonged, clinically evident seizures and shorter, clinically silent seizures; however, their effect on cerebral tissue oxygenation is unclear. We therefore examined the hypothesis that the increase in oxygen delivery during postasphyxial seizures might be insufficient to meet the needs of increased metabolism, thus causing a fall in tissue oxygenation, in unanesthetized near-term fetal sheep in utero (gestational age 1251 days). Fetuses were administered an infusion of the specific adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine, followed by 10 mins of asphyxia induced by complete umbilical cord occlusion. The fetuses then recovered for 3 days. Sixty-one episodes of electrophysiologically defined seizures were identified in five fetuses. Tissue PO₂ (tPO₂) did not change significantly during short seizures (<3.5 mins), 5.20.2 versus baseline 5.60.1 mm Hg (NS), but fell to 2.20.2 mm Hg during seizures lasting more than 3.5 mins (P<0.001). During prolonged seizures, cortical blood flow did not begin to increase until tPO₂ had begun to fall, and then rose more slowly than the increase in metabolism, with a widening of the brain to blood temperature gradient. In conclusion, in the immature brain, during prolonged, but not short seizures, there is a transient mismatch between cerebral blood flow and metabolism leading to significant cerebral deoxygenation.