Monitoring of CBFV and time characteristics of oxygen-induced acute CNS toxicity in humans

Background: Hyperbaric oxygen can cause central nervous system (CNS) toxicity with seizures. We tested the hypothesis that CNS toxicity could be predictable by cerebral blood flow velocity (CBFV) monitoring. Method: We monitored 369 mandatory oxygen tolerance tests (30 min, 280 kPa O2) by video-documentation and since May 2005 by additional CBFV registration (n = 61). Results: The onset of early manifestations of CNS toxicity was documented in 11 of 369 tests within 22 ± 3 min. These included twitches and/or agitation, 6 of 11 and tonic–clonic seizures in 5 of 11 cases. In both cases with CBFV monitoring, an increase in CBFV preceded symptom onset, once followed by seizure, once without seizure after timely oxygen reduction. Conclusions: During exposure to 280 kPa oxygen at rest a constant delay of approximately 20 min precedes the onset of central nervous oxygen toxicity. An increase in CBFV may indicate the impending seizure.