Introduction

A traumatic brain injury, commonly known as a TBI, is “an acquired insult to the brain from an external mechanical force” that will result in many different impairments of cognition or the general function of a particular action.¹ TBIs have widely affected individuals and the majority of cases end up being untreatable. However, among the many prospects of therapies, one that is considered regularly is hyperbaric oxygen therapy (HBOT). 

HBOT is a form of treatment where the patient inhales pressurised pure oxygen within a room or chamber. The pressure is gradually increased to above atmospheric pressure. The main observation is that the body takes in more oxygen than it normally would at regular pressure levels. This can eventually lead to therapeutic effects. 

There are various cases in which HBOT is an ideal form of treatment;

• Wound healing: for individuals who may have difficulty healing their wounds 
• Reduction in inflammation: this can help reduce the effects of autoimmune and neuroinflammatory diseases
• Infections: high oxygen concentration in the body can be deadly to bacteria causing infections within the person’s body
• Radiation therapy: this can be used to manage the side effects of radiation therapy 

In this article, we will be discussing the possible advantages and disadvantages regarding the use of HBOT to treat traumatic brain injuries. 

Understanding TBI

Over recent years, TBIs have been one of the leading causes of disability or, in worst-case scenarios, death. TBIs have negative implications for individuals, especially older patients. A study found that the number of patients admitted with TBIs increased with age.² TBIs can result from any form of physical damage directly to the head. This can occur in many ways, such as falls, vehicle-related collisions, violence, sports injuries (the most common), explosions, and more. 

There are many ways to classify TBIs. However, the most common way is through the Glasgow Coma Scale (GCS).³ This is a measurement that tests the level of consciousness in a person who has suffered a head injury. Components assessed during the GCS include eye, verbal, and motor responses. Each category is scored out of five, and the final result is totaled, where the lower the score, the more dysfunction occurs because of the TBI. 

Mild TBI

TBIs range in severity and are therefore categorised differently. The first classification is mild TBI. 

Physical symptoms of mild TBIs involve: 

• headache 
• nausea 
• fatigue 
• problems with speech
• sensory deficits 

Cognitive and behavioural symptoms could follow, such as: 

• loss of consciousness 
• memory problems 
• sudden mood changes 
• difficulty sleeping 

Moderate to severe TBI

These have similar symptoms to mild TBIs, except the symptoms have a quicker onset and are more severe. Due to the increased damage in these cases, treatment can range in efficacy. 

When TBI occurs, forceful contact with an object results in various alterations in the affected area. Such changes include shearing and strain, where the nerve fibres are stretching and tearing, and become damaged by the process. 

Contrecoup and coup injuries are other mechanisms where the brain crashes or collides with the skull, and the nerve fibres get destroyed. Brain swelling increases the intracranial pressure within the skull, which can lead to compression of various brain structures. Similarly, haemorrhages also increase pressure within the skull, and this can also cause brain compressions.

Overview of HBOT

There are many key principles behind HBOT. Firstly, increased oxygen levels elevate the concentration of oxygen being carried around by blood cells. Therefore, more respiration occurs within the body, providing energy for movement and muscle contractions. HBOT can also induce vasoconstriction or the narrowing of the blood vessels. This reduces the overall blood flow, decreasing inflammation and swelling. 

Due to the increase in oxygen, partial pressure can arise within the body and help to kill bacteria via white blood cells and complement antibiotic actions. 

Among new principles associated with HBOT, it can also promote the development of new blood vessels in the body in a process called neovascularisation. This can benefit health in many ways, and HBOT can be seen as an effective treatment for TBIs. 

The scientific basis for HBOT in TBI

HBOT can induce a reduction in inflammation as well as oxidative stress. The anti-inflammatory effects mitigate the secondary injury cascade as the pro-inflammatory cytokines are suppressed, and the increasing oxygen availability can help the immune cells execute their function and limit the extent of damage. Oxidative stress occurs when there is a shift in the balance of reactive oxygen species, which can harm the cell by damaging the DNA, protein, or lipids.⁴ Through the increase in oxygen, the body can counteract oxidative stress and allow it to act as a substrate for any antioxidant enzymes. The damaging effects of free radicals are lowered, and therefore, a more balanced redox state can be achieved in the brain that is injured. 

There have been many studies in the past which have implied that the use of HBOT in treating TBI can stimulate neurogenesis as well as angiogenesis. Under hyperbaric conditions, there will be an increase in the oxygen flow through the blood to support the proliferation and survival of neural precursor cells that can later form neurons. With more newly developed blood vessels being present, there can be increasing blood flow to the damaged brain following a TBI, and this can help contribute to the regeneration of damaged neural circuits in the brain. Angiogenesis and neurogenesis can work hand in hand to complement the growth of new blood vessels and neurons to treat and reduce the overall impact of a TBI. 

Clinical applications and evidence

Many studies have been conducted to determine HBOT’s usefulness as a treatment; however, there is no grounded evidence that the use of HBOT can be used to treat TBI, especially considering the heterogeneity of TBIs across humans. Therefore, the efficacy of clinical HBOT is considered controversial.⁵ 

Many research studies vary in results. There is evidence in favour of health improvements and cognitive functions, but the varying ability of TBI among different individuals makes it hard to draw conclusions on its efficacy.⁶ 

Even though there are alleviations of some of the symptoms of TBI, there are some drawbacks to the treatment itself. Potential risks of this treatment are barotrauma, ear or sinus discomfort, and oxygen toxicity. 

Respiratory problems are considered contraindications for HBOT treatment as the procedure may endanger the individual. Individuals who are pregnant, suffer from cardiovascular disease, or have a history of seizures are also more at risk if undertaking this treatment and are recommended to avoid HBOT to prevent any further damage.

HBOT protocols for TBI

Typical protocols for HBOT range in their treatment time and number of required sessions. A regular session lasts from 40 minutes to two hours, depending on the atmospheric pressure the patient is exposed to, how much is needed for the patient, and how much pressure the patient can handle. Continuous exposure to such high pressure for a long period could be fatal. The frequency of how often the patient must receive treatment from HBOT varies. However, the most common protocols involve daily sessions for several weeks to see improvements. 

As mentioned, HBOT must be administered at different levels of atmospheric pressure, which tend to be expressed as ATA (atmospheres absolute). Common pressure tends to be 1 ATA (sea level), but the majority of long-term treatments range from 1.5 to 3 ATA. 

Criticisms and controversies

Scepticism persists within the scientific community regarding the use of HBOT. The reason for these claims is that there is limited conclusive evidence to support the efficacy of HBOT for certain conditions, including TBI. Further critiques relate to the quality of the evidence gathered thus far, such as wanting more randomised controlled trials (RCTs). 

Publication bias has also been a concern, and many critics have questioned the validity of publications. A paper can, at times, build a completely wrong perception and image of the treatment.

Possible areas of improvement are having optimal protocols, patient selection criteria, and a better understanding of the mechanism of action to predict any possible issues and avoid them. 

Summary

Overall, HBOT is a promising treatment pathway which could be used in the future to treat TBIs and other neurological dysfunctions due to its potential to aid the body in its recovery. However, due to the risks associated with the treatment and the heterogeneity of TBI, it proves difficult to suggest HBOT as a frontline treatment. With the improving technology in science, the limitations of this treatment could be overcome in pursuit of treating many diseases.