Brain function after near-term birth. The effects of hypoxemia and hypotension.

This thesis describes the effects of hypoxemia and hypotension on brain cell function and brain metabolism in the near-term born lamb. Electrocortical brain activity (ECBA), which was used as a measure of brain cell function, was correlated to measures of energy failure and brain cell damage. Lambs were delivered near-term. Hypoxemia was induced by stepwise reduction of the inspired oxygen concentration. Hypotension was induced by stepwise withdrawal of blood. Flow in the left carotid artery and cerebral arterial blood gases were determined at the end of each hypoxemic or hypotensive level to calculate cerebral O2-supply. Furthermore, changes in cerebral O2-supply were monitored with near-infrared spectroscopy. For each individual lamb, the threshold of cerebral O2-supply for maintenance of ECBA was calculated. The concentrations of purines, pyrimidines and excitatory amino acids were determined in liquor cerebrospinalis. Overall threshold levels of cerebral O2-supply for the maintenance of ECBA were significantly different (p