Electroencephalographic (EEG) Changes Accompanying Normal Breathing of Concentrated Oxygen (Hyperoxic Ventilation) by Healthy Adults: A Systematic Review

Introduction: Divers often increase their fraction of inspired oxygen (FiO₂) to decrease their risk of decompression sickness. However, breathing concentrated oxygen can cause hyperoxia, and central nervous system oxygen toxicity (CNS-OT). This study aims to review the literature describing hyperoxic ventilation's effect on the electroencephalogram (EEG), thus exploring the potential for real-time detection of impending CNS-OT seizure. Methods: We searched Medline, Embase, Scopus, and Web of Science for articles that reported EEG measures accompanying hyperoxic ventilation (FiO₂ = 1.0) in healthy participants. We included peer-reviewed journal articles, books, and government reports with no language or date restrictions. Randomised controlled trials and cross-over studies were included; case reports were excluded. We used the Newcastle-Ottawa scale to evaluate evidence quality. Results: Our search strategy returned 1025 unique abstracts; we analysed the full text of 40 articles; 22 articles (16 studies) were included for review. Study cohorts were typically small, and comprised of male non-divers. We discovered a variety of EEG analysis methods: studies performed spectral analysis (n = 12), the analysis of sensory-evoked potentials (n = 4), connectivity/complexity analysis (n = 3), source localization (n = 1), and expert qualitative analyses (n = 4). Studies of severe exposures (long duration at hyperbaric pressure) typically reported qualitative measures, and studies of mild exposures typically reported quantitative measures. Conclusions: There is a need for a large randomised controlled trial (RCT) reporting quantitative measures to better understand hyperoxic ventilation's effect on EEG, thus enabling the development of real-time monitoring of CNS-OT risk.