How Hyperbaric Oxygen Therapy Works: A Plain-Language Guide for Canadian Patients

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TL;DR: Hyperbaric oxygen therapy is a treatment in which you breathe 100 percent oxygen inside a sealed chamber pressurised above normal atmospheric pressure. The pressure dissolves far more oxygen into your blood plasma than normal breathing allows, so oxygen reaches tissues that injury, infection, or poor circulation has cut off. Canadian hospitals and regulated facilities use it for recognised conditions such as carbon monoxide poisoning, non-healing diabetic wounds, radiation injury, decompression sickness, and severe infections. A typical session lasts 90 to 120 minutes at 2.0 to 2.4 atmospheres absolute, and most approved courses run 20 to 40 sessions.

If your physician has mentioned hyperbaric oxygen therapy as a possible treatment, you probably want to understand what is actually happening inside the chamber and why it might help your specific condition. This guide explains the physics, biology, and clinical practice of hyperbaric oxygen therapy in plain language, with citations to peer-reviewed research and links to Canadian resources. Canada Hyperbarics is an independent directory of hospitals and regulated facilities offering hyperbaric oxygen therapy across the country.

What is hyperbaric oxygen therapy?

Hyperbaric oxygen therapy is a medical treatment in which a patient breathes 100 percent oxygen while inside a chamber pressurised to between 1.4 and 3.0 atmospheres absolute (ATA). One ATA equals normal sea-level air pressure. Most approved Canadian protocols use 2.0 to 2.4 ATA, which is roughly the pressure you would feel about 10 to 14 metres underwater. The treatment is delivered in either a single-person chamber, called a monoplace chamber, or a multi-person chamber, called a multiplace chamber, where several patients sit together while wearing oxygen masks or hoods.

The therapy is sometimes shortened to HBOT or HBO. It has a long history in diving medicine, where it was first used to treat decompression sickness in commercial and military divers. Over the past several decades, research has expanded its use to a defined list of medical conditions where the underlying problem is oxygen deprivation, infection, or impaired tissue repair. Health Canada regulates the chambers as Class III medical devices, and the Undersea and Hyperbaric Medical Society (UHMS) publishes the international list of recognised indications.

How does pressure and oxygen work together inside the chamber?

Two physical laws explain almost everything about how hyperbaric oxygen therapy works at the body level. The first is Henry’s law: the higher the pressure of a gas above a liquid, the more of that gas dissolves into the liquid. Your blood plasma is the liquid in this case, and oxygen is the gas. When you breathe ordinary air at sea level, your red blood cells are already about 97 percent saturated with oxygen, so almost no extra oxygen dissolves directly into the plasma itself. Inside a hyperbaric chamber at 2.4 ATA breathing 100 percent oxygen, the amount of oxygen dissolved in plasma rises by roughly 10 to 20 times.

The second is Boyle’s law: at higher pressure, gas bubbles inside the body shrink. This is the principle behind treating decompression sickness and arterial gas embolism, where bubbles trapped in tissue or blood vessels are physically reduced in size by pressure and then dissolved over time as oxygen replaces the inert gas inside them.

The combined effect is that oxygen reaches tissues that normally cannot receive enough of it. Damaged or infected tissue often has poor blood flow, and red blood cells struggle to squeeze through swollen or narrowed capillaries. Plasma, which is far smaller than red cells, can still flow through these tight spaces and now carries a useful payload of oxygen with it. This is the foundational mechanism behind every clinical use of hyperbaric oxygen therapy (Lindenmann et al. 2022).

What does the extra oxygen actually do in the body?

Once the dissolved oxygen reaches tissues, it triggers a cascade of biological effects that researchers have mapped in detail over the past two decades. Based on articles retrieved from PubMed, hyperbaric oxygen therapy works through several distinct but overlapping pathways:

1. It restores oxygen to hypoxic tissue. Wounds, infections, and radiation-injured tissue often run on too little oxygen for normal cellular repair. Restoring oxygen lets cells generate energy, build proteins, and clear waste again.
2. It promotes new blood vessel growth (angiogenesis). Repeated sessions stimulate the release of growth factors that encourage the body to build new capillaries into damaged areas. This is why a course of treatment usually requires 20 to 40 sessions rather than one or two.
3. It modulates inflammation. Hyperbaric oxygen reduces the activity of inflammatory signalling proteins such as nuclear factor kappa-B (NF-kB) and tumour necrosis factor, while supporting the body’s native anti-inflammatory pathways.
4. It enhances the immune response to certain bacteria. Oxygen is directly toxic to bacteria that live in low-oxygen environments, including the species responsible for gas gangrene and necrotising soft tissue infections. Oxygen also strengthens white blood cell killing power.
5. It mobilises stem cells. Repeated sessions release stem and progenitor cells from the bone marrow into circulation, where they can travel to sites of injury and contribute to tissue repair.
6. It reduces gas bubbles. In decompression sickness and air embolism, the pressure itself dissolves trapped bubbles.

A 2022 literature survey in Biomedicines mapped these effects across signalling proteins including NF-kB, hypoxia-inducible factor, nitric oxide, vascular endothelial growth factor, and the PI3K/AKT pathway, and concluded that hyperbaric oxygen tends to restore physiological balance rather than push any single pathway in one direction (Lindenmann et al. 2022). A 2021 review in Biomolecules describes similar mechanisms in the brain, including effects on mitochondrial function, oxidative stress regulation, and neuroinflammation (Gottfried et al. 2021).

Which conditions does Canadian medicine approve for hyperbaric oxygen therapy?

Canadian hospitals and regulated facilities follow the UHMS-recognised indications list, which currently includes 15 conditions where there is sufficient evidence to support treatment. Coverage by provincial health insurance is condition-dependent and varies by province. The table below summarises the main recognised indications and the typical evidence basis.

Condition	How HBOT helps	Typical course
Carbon monoxide poisoning	Speeds clearance of CO from haemoglobin and reduces delayed neurological injury	1 to 3 sessions
Decompression sickness	Shrinks gas bubbles in blood and tissue	1 to several sessions
Arterial gas embolism	Same as above, urgent treatment	1 to several sessions
Diabetic foot ulcers (selected)	Restores oxygen to hypoxic tissue, supports new vessel growth	20 to 40 sessions
Late radiation injury	Stimulates new blood vessels in radiation-damaged tissue	30 to 40 sessions
Compromised skin grafts and flaps	Improves oxygen delivery to threatened tissue	10 to 20 sessions
Necrotising soft tissue infections	Direct antibacterial effect plus immune support	5 to 10 sessions
Crush injury and acute traumatic ischaemia	Reduces tissue swelling and supports oxygen delivery	up to 12 sessions over 2 to 7 days
Refractory osteomyelitis	Improves antibiotic effectiveness and bone healing	20 to 40 sessions
Sudden sensorineural hearing loss	May improve hearing recovery if started within 14 days	10 to 20 sessions
Central retinal artery occlusion	Maintains retinal oxygen until circulation can be re-established	variable, urgent
Severe anaemia from exceptional blood loss	Provides oxygen when red blood cells cannot	variable

The 2023 International Working Group on the Diabetic Foot guideline gave a conditional supportive recommendation for hyperbaric oxygen in selected diabetic foot ulcers where best standard of care has not achieved healing (Chen et al. 2023). A 2023 review in the Indian Journal of Orthopaedics summarised the orthopaedic indications, including chronic osteomyelitis and avascular necrosis, and noted the same UHMS framework (Jeyaraman et al. 2023). Emerging or investigational uses, such as long COVID, post-traumatic stress disorder, and fibromyalgia, are still under research and not yet approved for routine reimbursement in Canada (Sippel et al. 2024).

What happens during a hyperbaric oxygen therapy session?

A typical session at a Canadian hyperbaric facility follows a predictable pattern. Knowing what to expect can take a lot of the anxiety out of the first visit.

1. Pre-session screening. Staff confirm your medical history, check that you have no untreated lung problems or recent ear infection, and remove any prohibited items such as lighters, electronics, or oil-based cosmetics. You change into a 100 percent cotton gown.
2. Entering the chamber. In a monoplace chamber you lie on a sliding stretcher and the chamber is sealed behind you. In a multiplace chamber you walk in and sit in an aircraft-style seat. The technician communicates with you by intercom and watches you through windows or cameras throughout the session.
3. Compression (10 to 15 minutes). The chamber is slowly pressurised. Your ears will need to be cleared, the same way they do during an aircraft descent. You can yawn, swallow, or perform a gentle Valsalva manoeuvre.
4. Treatment phase (60 to 90 minutes). You breathe 100 percent oxygen at full pressure. In a monoplace chamber the entire chamber is filled with oxygen. In a multiplace chamber you wear a mask or hood. Most patients read, watch a screen mounted outside the window, listen to music through approved speakers, or sleep.
5. Air breaks. Some protocols include a 5-minute break breathing room air to reduce the risk of oxygen toxicity.
6. Decompression (10 to 15 minutes). Pressure is released slowly. Your ears will pop again as pressure normalises.
7. Post-session check. Staff confirm you feel well before discharge. Most patients drive themselves home.

Total time at the facility is usually about two hours. Whether you need 20 sessions, 30 sessions, or 40 sessions depends on your condition and how your body responds. Your physician and the hyperbaric medical team set the protocol together.

What are the side effects and risks?

Hyperbaric oxygen therapy is generally safe when delivered by trained staff in a regulated facility, but it is not risk-free. The most common side effects are minor and temporary.

• Ear pressure or discomfort (barotrauma): The most common issue. Usually managed by clearing your ears during compression. Severe cases may require slowing or pausing the dive.
• Temporary near-sightedness: A reversible change in the lens of the eye that develops in some patients after long courses of treatment. It typically resolves over several weeks after the course ends.
• Sinus discomfort: Similar to ear pressure, usually mild.
• Claustrophobia: Some patients feel anxious in the chamber. Multiplace chambers, mild sedation, or simple acclimatisation usually resolve this.
• Oxygen toxicity: Rare at standard pressures and treatment times. Can cause seizure-like events. Air breaks reduce this risk.
• Pulmonary changes: Very rare but possible with long courses; typically reversible.

Certain conditions are absolute contraindications, including untreated pneumothorax (collapsed lung). Others are relative contraindications that need careful screening, including some chemotherapy agents, recent ear surgery, severe claustrophobia, and uncontrolled seizure disorder. Your referring physician and the hyperbaric medical team will review these before approving treatment. Read more in our overview of commonly asked questions about hyperbaric oxygen therapy.

How do Canadian patients access hyperbaric oxygen therapy?

Access to hyperbaric oxygen therapy in Canada depends on three things: your condition, your province, and the type of facility nearest you. For recognised indications, treatment is generally provided at major hospitals with regulated multiplace chambers, and is usually covered by your provincial health plan when ordered through a hospital-based referral.

• Ontario residents may have coverage through OHIP for approved hospital-based treatments.
• British Columbia residents may have coverage through MSP.
• Alberta residents may have coverage through AHCIP.
• Quebec residents may have coverage through RAMQ.
• Other provinces use their respective provincial plans (Manitoba Health, Saskatchewan Health, MSI in Nova Scotia, Medicare NB, PEI Health, MCP in Newfoundland and Labrador, and territorial plans in NWT, Yukon, and Nunavut).

Coverage rules differ by condition and province, and not every recognised condition is automatically covered everywhere. Some patients also self-fund treatment at private facilities for off-label or emerging indications. Visit our coverage guide for province-by-province detail, and see our directory of hospitals and regulated facilities across Canada.

If you want to dig into the underlying research, our research database contains thousands of peer-reviewed studies on hyperbaric oxygen therapy with plain-language summaries.

Frequently asked questions

Is hyperbaric oxygen therapy the same as breathing oxygen through a nose cannula?

No. Standard oxygen therapy raises the oxygen concentration of the air you breathe at normal atmospheric pressure. Hyperbaric oxygen therapy does both: it gives you 100 percent oxygen and it raises the surrounding pressure. The added pressure is what dissolves significantly more oxygen into your plasma.

Will I feel anything inside the chamber?

You will feel pressure changes in your ears during compression and decompression, similar to landing in an aircraft. The chamber may feel warmer during compression and cooler during decompression. Most patients otherwise feel normal during the treatment phase.

How many sessions will I need?

It depends on your condition. Carbon monoxide poisoning may need only one to three sessions. Late radiation injury and refractory osteomyelitis often require 30 to 40 sessions. Diabetic wound healing protocols typically run 20 to 40 sessions. Your hyperbaric medical team will recommend a course based on the published protocol for your specific condition and adjust based on response.

Can I bring my phone or a book into the chamber?

Personal electronics are generally not allowed because of fire risk in an oxygen-rich environment. Most facilities provide approved reading materials or external entertainment such as a screen visible through the chamber window. Ask the facility ahead of time about their specific rules.

Will my hair or skin be affected?

The chamber environment will not chemically change your hair or skin, but you must arrive without oil-based hair products, makeup, or moisturisers. These are flammable in a high-oxygen atmosphere. Staff will give you a checklist before your first session.

Is hyperbaric oxygen therapy painful?

The treatment itself is not painful. The most common discomfort is ear pressure during compression, which is managed the same way as on a flight. If you cannot equalise your ears, the technician can slow the compression rate or pause until you are comfortable.

Can I drive myself home after a session?

Yes, in nearly all cases. Most patients feel normal immediately after a session and continue with their day. If your specific medical situation suggests otherwise, your hyperbaric team will tell you in advance.

Is hyperbaric oxygen therapy covered by my provincial health plan?

For recognised conditions delivered through a hospital-based referral, treatment is generally covered. Coverage rules differ by province and by condition. Self-pay private treatment is also available for some emerging indications. See our province-by-province coverage guide for details.

What is the next step if you think hyperbaric oxygen therapy could help you?

If you suspect that hyperbaric oxygen therapy could be appropriate for your condition, the first conversation should be with your family physician or the specialist managing the underlying problem. Bring a written list of your symptoms, the treatments you have already tried, and the specific question of whether a hyperbaric referral is appropriate. Ask whether your hospital has a hyperbaric program, or whether they refer to a centre in another city. Canada Hyperbarics maintains a directory of hospitals and regulated facilities offering hyperbaric oxygen therapy across the country, organised by province.

External resources you may also find useful:

• Health Canada – federal regulator for medical devices and drug safety
• Undersea and Hyperbaric Medical Society (UHMS) – international authority on recognised indications
• Canadian Undersea and Hyperbaric Medical Association (CUHMA)
• PubMed – peer-reviewed research literature

References

• Lindenmann J, Kamolz L, Graier W, Smolle J, Smolle-Juettner FM. Hyperbaric Oxygen Therapy and Tissue Regeneration: A Literature Survey. Biomedicines. 2022;10(12):3145. Read summary · DOI
• Gottfried I, Schottlender N, Ashery U. Hyperbaric Oxygen Treatment – From Mechanisms to Cognitive Improvement. Biomolecules. 2021;11(10):1520. Read summary · DOI
• Jeyaraman M, Sami A, Nallakumarasamy A, et al. Hyperbaric Oxygen Therapy in Orthopaedics: An Adjunct Therapy with an Emerging Role. Indian Journal of Orthopaedics. 2023;57(5):748-761. Read summary · DOI
• Chen P, Vilorio NC, Dhatariya K, et al. Guidelines on interventions to enhance healing of foot ulcers in people with diabetes (IWGDF 2023 update). Diabetes/Metabolism Research and Reviews. 2023;40(3):e3644. Read summary · DOI
• Sippel LM, Hamblen JL, Kelmendi B, et al. Novel Pharmacologic and Other Somatic Treatment Approaches for Posttraumatic Stress Disorder in Adults. American Journal of Psychiatry. 2024;181(12):1045-1058. Read summary · DOI

Medical disclaimer: This content is for informational purposes only and does not constitute medical advice. Hyperbaric oxygen therapy is a regulated medical treatment that should only be undertaken under the supervision of qualified medical professionals at accredited hospitals and regulated facilities. Always consult your physician about whether hyperbaric oxygen therapy is appropriate for your specific medical situation.