Hyperbaric Oxygen Therapy For Stroke Recovery

What is hyperbaric oxygen therapy and can it help in post-stroke recovery? Find out in this article which will delve into the latest research in this area to find out if this treatment can help with the recovery process following a stroke.

What is hyperbaric oxygen therapy (HBOT)?

Hyperbaric oxygen therapy is the use of oxygen at a higher pressure than oxygen in the atmosphere (usually two to three times higher) so that oxygen is more easily available in the body; oxygen is thought to be of benefit in the recovery process of cells under stress or damage due to a lack of oxygen.

What is a stroke?

A stroke, put simply, is a lack of blood flow to the brain that causes brain cell injury and brain cell death. It can be thought of as a brain attack in the same way that a lack of blood flow to the heart can cause a heart attack. There are two main types of stroke; ischaemic and haemorrhagic. Ischaemic stroke is caused by a blockage in the vessels supplying brain cells with blood flow, thereby depriving brain cells of vital oxygen. Haemorrhagic stroke is when there is a bleed in the vessels of the brain which also prevents blood from flowing in the correct way to the brain’s cells.

This article looks at the current evidence to see whether there is a role for hyperbaric oxygen therapy in stroke recovery.

A stroke has many effects on the brain and therefore the body as a whole. The effects of a stroke on the brain will primarily depend on the area of the brain affected. For example, a stroke in the frontal lobe may affect thinking, emotions and decision-making, whereas a stroke in the occipital lobe (back of the brain) can cause visual disturbance or blindness, and there are many different symptoms in between. The effects of a stroke on the body can be sensory loss or movement loss in any part of the body, depending on the area of the brain affected. These effects can be life-changing and severe, from losing the ability to walk to losing the ability to speak.

What challenges are faced by those recovering from a stroke?

Common challenges faced by those recovering from a stroke are trying to regain any functions they have lost and maintaining an independent life. These may include:

• thinking or memory problems
• difficulty in concentrating
• loss of movement 
• difficulty in swallowing 
• difficulty in controlling bowel or bladder movements
• psychological effects, which can commonly cause depression and anxiety¹

Other challenges include those faced by partners or relatives of a stroke survivor. It is important that those caring for stroke survivors are informed about the effects of the stroke and their role in helping their loved one to recover. They will have to be patient and positive, be prepared for any personality or behavioural changes in their loved one and be willing to help with physiotherapy and any adjustments needed. Most of all, they need to care for themselves to be in a position to help their loved one in the healing process.

What are the principles behind hyperbaric oxygen therapy?

Increased oxygen delivery to tissues

There is increased oxygenation of tissues following HBOT for three reasons: 

• Breathing in pure oxygen allows for increased oxygenation of blood from the lungs, as they now have a higher oxygen content. 
• The high pressure also increases blood oxygen concentration, as it causes more oxygen to be dissolved in the blood.²
• The presence of gas bubbles in the blood (e.g. in decompression sickness) is decreased, allowing for increased oxygen uptake.

Reduction of inflammation

Investigations have been undertaken to determine the role of HBOT in reducing inflammation. So far, current research has shown that HBOT has been shown to change the makeup of immune cells that are activated in hyperoxic regions and, as a result, may help reduce inflammation; however, this needs to be investigated further.

Promotion of tissue repair and regeneration

In clinical practice, HBOT has been shown to improve the healing time of wounds and promote repair.³ This has been demonstrated in conditions such as diabetic foot ulcers, microbe-infected wounds, thermal burns, traumatic wounds and vascular insufficiency ulcers.  It is thought that HBOT reduces the production of certain toxins in the wound and increases the microbicidal effects of certain white blood cells. 

What conditions can HBOT treat?

There is currently a limited list of conditions approved for treatment with HBOT; however, one must note that strokes are not one of these conditions as of yet. Approved conditions include air embolism, severe anaemia, diabetic foot ulceration, carbon monoxide poisoning, radiation damage, necrotising soft tissue infections and malignant otitis externa.

Scientific evidence

Three randomised controlled trials published to date show that there is no benefit to hyperbaric oxygen therapy for strokes in the acute, sub-acute or chronic phase.⁴

As there were many different factors at play here, however, the results are not generalisable; the type of stroke and the dosage of hyperbaric oxygen given tended to vary to a significant degree. Additionally, there was a lack of provision for reporting of adverse events. While there are no current concerns for any life-threatening consequences of hyperbaric oxygen therapy, there was a significantly high discontinuation rate from the studies, with neurological deterioration reported in some cases.

Currently, there is not  enough evidence either for or against hyperbaric oxygen therapy for the treatment of strokes and further studies are needed.

Review of clinical studies and findings

Most studies on HBOT and stroke recovery have been observational studies with flawed design and implementation. As a result, the evidence produced by them is not conclusive.

Many of the findings of HBOT in improving neurological function have been put together by looking at animal studies and the effects in animals that can be translated to humans. This research is not necessarily able to be transferred over to humans directly and, consequently, does not represent conclusive proof of effectiveness in humans. 

Some animal studies have shown a decrease in inflammatory markers and an antioxidant effect of HBOT. Additionally, there has been a link between HBOT and neuroprotective effects after a stroke, such as the prevention of apoptosis (cell death) after treatment with HBOT, again a finding in animal studies only.

HBOT administration protocol for strokes

The protocol for administration undertaken most often seems to be 2 hours in an HBOT chamber. The chamber can either be a monoplace or a multiplace chamber. The monoplace chamber allows only one individual at a time in the oxygen chamber, similar to an MRI machine. The multiplace chamber usually has a number of people inside, including chamber assistants. Each person puts on a face mask which creates the hyperbaric environment.

There is a clear timeline of when HBOT can be used in stroke patients. This is within 12 hours of illness onset. This is a narrow window in which to start therapy taking into account other treatments that have to be initiated first, including imaging. This may partly explain why HBOT has not been so well studied in stroke patients. The immobility of the oxygen chamber is another issue that complicates the provision of HBOT within the 12-hour recommended window of opportunity.

Each HBOT session typically lasts 2 hours per day, with a total of 30-40 sessions recommended for a complete treatment. This is an established protocol for wound treatment; however, no such protocol has been devised for stroke treatment as HBOT is not currently indicated for strokes.

Patient experience

What can you expect when undergoing HBOT? We cannot look at patient experiences of HBOT following a stroke as this has not been well documented. However, we can learn from the experiences of others undergoing HBOT to treat other conditions. 

In one study, patients were interviewed about their experiences; before treatment, most patients had little understanding of HBOT. There was a great deal of anxiety among most patients before the start of their treatment plan.⁵ Most of this was due to the uncertainty of what would happen inside the chamber. Another common issue was boredom during the treatment. Most people questioned reported that the chamber felt normal and their experience was positive overall, leading them to continue treatment. The only adverse event recorded by these patient interactions was visual disturbance, most likely due to oxygen-induced myopia which lasts the duration of the treatment but typically clears up in around 4 weeks.

Safety and risks

There are a few safety measures that need to be observed while inside the hyperbaric chamber. These are mainly to do with the fact that environments high in oxygen concentration present a high fire risk and any fire that does start will burn with much higher intensity and vigour. You cannot bring a lighter, or any battery-powered devices that generate heat, inside the chamber due to the combustible nature of such items.

As with all treatments, there are side effects with HBOT. The most common side effects reported include:

• ear discomfort and/or pain
• sinus pain
• visual disturbance
• claustrophobia

More serious adverse events include lung collapse. In rare cases, a person can suffer from oxygen poisoning which can lead to seizures, fluid in the lungs and lung failure.⁶

Patient selection criteria

There are certain criteria that exclude a person from being eligible for hyperbaric oxygen therapy. These include people who have recently undergone an ear operation, those with a high temperature or a cold, certain lung conditions such as bullous lung disorders and untreated pneumothorax.

Future directions and research

With the evidence not being strong in either direction, there is a lot of scope for further research. There is a need for more observational studies especially ones that are well-designed and minimise any bias that may occur. There could also be the adoption of objective outcome measures to allow effective comparison between different studies.

Summary

To conclude, hyperbaric oxygen therapy is a treatment that is established for certain conditions but not yet for strokes. The evidence is not compelling either for or against its use. When the evidence is lacking to support its use, it cannot be recommended as a treatment for recovery after a stroke. Further evidence needs to be collected about this treatment which is elusive due to the nature of intervention that is required, especially in the acute phase of a stroke. Better-designed studies will need to be conducted if we are to find out whether it can benefit stroke patients.