Oxygen toxicity seizure mimics.

INTRODUCTION: Oxygen toxicity seizures (OTS) are a well-recognised complication of hyperbaric oxygen treatment (HBOT). As such, seizure-like activity during HBOT is usually presumed to be a result of central nervous system oxygen toxicity (CNS-OT). Four cases are reported here where causes other than CNS-OT were determined as being the likely cause of the seizure; causes we have labelled 'OTS mimics'. Through review of the current literature, and our hyperbaric medicine unit's experience to date, we aimed to highlight the relevance of these OTS mimics, as the potential for significant morbidity and mortality exists with incorrect diagnoses. METHODS: A retrospective review of the medical records of all patients treated at the Fiona Stanley Hospital and Fremantle Hospital hyperbaric medicine units who had a seizure during HBOT between November 1989 and June 2020. These events were reviewed to determine whether causes for seizures other than oxygen toxicity were evident. RESULTS: Four OTS mimics were identified: posterior reversible encephalopathy syndrome, pethidine toxicity, previous subarachnoid haemorrhage with resultant epilepsy, and severe hypoglycaemia. CONCLUSIONS: This case series highlights the need for caution when diagnosing an apparent OTS. Multiple conditions may mimic the signs and symptoms of oxygen toxicity. This creates scope for misdiagnosis, with potential for consequent morbidity and mortality. A pragmatic approach is necessary to any patient exhibiting seizure-like activity during HBOT, with suspicion for other underlying pathologies.

Oxygen toxicity seizures during United States Navy Treatment Table 6: An acceptable risk in monoplace chambers?

INTRODUCTION: Hyperbaric oxygen treatment (HBOT) may be complicated by oxygen toxicity seizures, which typically occur with hyperbaric partial pressures of oxygen exceeding 203 kPa (2 atmospheres absolute). All other hyperbaric units in Australia exclusively use a multiplace chamber when treating with United States Navy Treatment Table 6 (USN TT6) due to this perceived risk. The purpose of this study was to determine the safety of a monoplace chamber when treating decompression illness (DCI) with USN TT6. METHODS: A retrospective review of the medical records of all patients treated at Fiona Stanley Hospital Hyperbaric Medicine Unit with USN TT6 between November 2014 and June 2020 was undertaken. These data were combined with previous results from studies performed at our hyperbaric unit at Fremantle Hospital from 1989 to 2014, creating a data set covering a 30-year period. RESULTS: One thousand treatments with USN TT6 were performed between 1989 and 2020; 331 in a monoplace chamber and 669 in a multiplace chamber. Four seizures occurred: a rate of 0.59% (1/167) in a multiplace chamber; and none in a monoplace chamber, indicating no statistically significant difference between seizures in a monoplace versus multiplace chamber (P = 0.31). CONCLUSIONS: The rate of oxygen toxicity seizures in a monoplace chamber is not significantly higher than for treatment in the multiplace chamber. We conclude that using the monoplace chamber for USN TT6 in selected patients poses an acceptably low seizure risk.

Relaxation strategies and enhancement of hypnotic susceptibility: EEG neurofeedback, progressive muscle relaxation and self-hypnosis.

Hypnosis has been shown to be efficacious in a range of clinical conditions, including the management of chronic pain. However, not all individuals are able to enter a hypnotic state, thereby limiting the clinical utility of this technique. We sought to determine whether hypnotic susceptibility could be increased using three methods thought to facilitate relaxation, with particular interest in an EEG neurofeedback protocol which elevated the theta to alpha ratio. This was compared with progressive muscle relaxation and self-hypnosis. Ten subjects with moderate levels of susceptibility (2-7/12) were randomly assigned to each condition and assessed for hypnotic susceptibility prior to and upon completion of 10 sessions of training. Hypnotic susceptibility increased post-training in all groups, providing further evidence that operant control over the theta/alpha ratio is possible, but contrary to our predictions, elevation of the theta/alpha ratio proved no more successful than the other interventions. Nonetheless, all three techniques successfully enhanced hypnotic susceptibility in over half of the participants (17/30), a similar incidence to that reported using other methods. As previously reported, the majority who were not susceptible to modification were at the lower levels of susceptibility, and the greater increases tended to occur in the more susceptible subjects. However, here enhancement was disclosed in some at low levels, and capability was found of reaching high levels, both features not typically reported. Further research is warranted.