The role of HBO as a potential therapy option for brain injury has long been discussed. The theory being that by maximising oxygenation post–injury the area of healthy tissue loss due to ischaemia and oedema will be reduced and healthy brain function maintained, whilst optimising recovery. If effective, this could result in reduced morbidity and lessen the number of patients left with long-term residua such as physical, cognitive and communication difficulties.
Unfortunately, however, indications such as traumatic brain injuries and stroke have remained controversial due to limited numbers of randomised control trials and inconsistent outcomes.
Traumatic Brain Injuries (TBI):
There have been experimental animal studies involving HBOT in the treatment of TBI since the 1960s1. Clinical studies, however, have mostly provided case study or retrospective analysis with mixed outcomes. For example, Mao et al. 20102 found that HBOT improved outcome in severe injuries with improved EEG readings and Glasgow Coma Outcome scores, whereas conversely, Rockswold et al. 19923 found no improvement in recovery or disability.
Bennett et al. 20124 performed a meta-analysis of randomised trials with the conclusion that the addition of HBOT in the treatment of TBI may improve survival but not quality of life. Thus, current evidence has been unable to prove that the benefit of treatment outweighs the risks of exposure to hyperbaric oxygen. The European Committee on Hyperbaric Medicine (ECHM) therefore only recommended HBOT ‘in the context of an investigational study protocol’ and state that ‘it would be reasonable to consider HBOT in acute moderate-severe TBI’5.
Since this meta-analysis and the last ECHM conference there have been further randomised trials. Zhong et el. 20206 studied patients with severe head injuries with routine HBO therapy started 1 week after admission. At the end of the treatment period the group receiving the HBOT showed improved GCS and lower NIHSS scores.
Systematic reviews have shown that there is no decrease in mortality in stroke patients treated with HBOT within 6 months after presentation therefore, the ECHM ‘do not recommend HBOT use in the acute phase of stroke’5. Evidence is based on a limited number of randomised controlled trials that have shown variable results for improvement in disability with HBOT7. Further research is required to establish clear guidelines for practice.
Whilst there is insufficient evidence to support the use of HBO in acute stroke, ECHM highlighted potential use in chronic stroke, given select criteria. ‘It would be reasonable to consider HBOT in the frame of an investigational clinical study in a highly selected group of patients with chronic stroke who have clear evidence of metabolically dysfunctioning brain regions that are mismatching with the necrotic brain regions. Patients who are candidates for HBOT should be properly evaluated prior to therapy by standardized cognitive tests and by a functional imaging of the brain’5.
This recommendation is based on evidence from selected randomized controlled trials which have shown that HBO has the potential to activate neuroplasticity long after stroke onset. Namely, Efrati et al. 20138; who used SPECT/CT on 74 patients with a history of a stroke 6-36 months prior, with at least 1 motor dysfunction. Results showed an increase in neurological function and quality of life with increased benefit seen in those with a SPECT/CT area mismatch. Schiavo et al. 20209 also showed that HBOT may have a role to play in a combined approach to aid neuroplasticity and recovery after stroke.
For some time, there has been clinical observation that HBO may be of benefit in chronic stroke patients. Neubauer & End 198010 suggested a minimum of 20 treatments on review of their cohort of 122 patients with ischaemic strokes. Further studies with varying numbers of participants have shown clinical improvement in language fluency and motor paresis11. Hadanny et al. 202012 recognised that HBOT produced significant improvements in cognition with prognosis determined by functional analysis and baseline cognitive score rather than the nature of the type or location of the stroke. This is supported by other studies which show a significant improvement in memory measures, cognition, and physical abilities even years after the stroke event13,14.
Studies have utilised SPECT/CT and retrospective analysis of this imaging has shown good correlation as a predictor for positive clinical outcome following HBOT in post-stroke patients15.
Overall, there is much potential for further research in these areas with current evidence suggesting that HBOT may provide a benefit as an adjunct therapy in specific groups of head injury/stroke patients. The possibility of reducing the number of residual symptoms that patients are left with could have a significant impact on individual quality of life, as well as reducing the financial burden of lifelong care and continued healthcare input.