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 elevated pressures of oxygen can cause central nervous system oxygen toxicity (CNS-OT). This study aimed to review the literature describing the effect of hyperoxia on the electroencephalogram (EEG), thus exploring the potential for real-time detection of an 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 ± hyperbaric pressure) 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 1,025 unique abstracts; we analysed the full text of 46 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 localisation (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 reporting quantitative measures to better understand the effect of hyperoxia on the EEG, thus enabling the development of real-time monitoring of CNS-OT risk.