Background: The aim was to determine the hypoxic threshold for EEG suppression and cerebral hypoxanthine production in newborn piglets, with and without mixed acidosis.

Subjects: 14 newborn piglets in general anaesthesia.

Interventions: FiO2 was reduced in steps: 21, 14, 12, 10, 9,.., 5%. Seven of the piglets also received lactic acid and CO2(pH<7.1, apCO2=7-8kPa). Microdialysis from the cerebral cortex for hypoxantines was performed EEG was recorded and analyzed using a compressed spectral array program.

Results: Loss of EEG-power occurred in parallel with hypoxanthine-increase. The changes from baseline became significant at 8% FiO2 in non-acidotic piglets and 9% in acidosis (p<0.05), the difference being unexplained by MABP. Fast frequency band activity was more susceptible to hypoxia than slow ones.

Conclusion: Mixed acidosis increases brain sensitivity to hypoxia.