TL;DR: An hyperbaric oxygen therapy (HBOT) session takes 90 to 120 minutes door-to-door, runs at 2.0 to 2.4 atmospheres absolute (ATA) inside a pressurised chamber, and requires you to breathe 100% oxygen through a mask or hood. A standard treatment course is 20 to 60 daily sessions over 4 to 12 weeks. This guide walks through what happens at your first appointment, how to prepare, common side effects, and what to expect during the rest of the course.
Estimated reading time: 9 minutes. Last reviewed: 2026-05-30.
Before you arrive: pre-screening and preparation
Before your first chamber session you will meet with a hyperbaric medicine physician who reviews your referral, your medical history, and any imaging or laboratory results provided by your referring doctor. The pre-screening exists for two reasons: to confirm that HBOT is appropriate for your indication, and to identify any contraindications that need to be managed before treatment begins.
A chest X-ray is commonly ordered to rule out an undetected pneumothorax (collapsed lung) because increased ambient pressure during compression can rapidly worsen a pneumothorax. An ear, nose and throat (ENT) assessment may also be needed if you have a history of recurrent ear infections, sinus problems, or difficulty equalising middle-ear pressure when flying or scuba diving. If you cannot equalise effectively, the hyperbaric team may recommend tympanostomy tubes or another intervention before treatment.
Practical preparation checklist
- Wear all-cotton clothing. Synthetic fibres (polyester, nylon, fleece) are restricted inside the chamber because they can build static electricity in a pure-oxygen environment. Most units supply 100% cotton scrubs at the door if you arrive in synthetic clothing.
- Remove all cosmetics, lotions, hairspray, perfume, and lip balm. Petroleum-based products are flammable in high-oxygen environments. Wash your face and hair before the appointment if you can.
- No nail polish, no jewellery, no contact lenses. Glasses are fine. Remove watches, hearing aids, and any electronic devices unless specifically cleared by the unit.
- Eat a light meal beforehand. Avoid carbonated drinks, large meals, and gum chewing for 1 to 2 hours before the session because gas expansion at altitude can cause discomfort during decompression.
- Hydrate, but do not over-hydrate. Most sessions do not allow bathroom breaks once the chamber is sealed. Use the washroom right before your session.
- Stop smoking before and during the treatment course. Smoking constricts blood vessels and directly counteracts the therapeutic effect of HBOT. Most hyperbaric units strongly recommend complete cessation.
- Bring something to occupy yourself. Sessions are 60 to 90 minutes of chamber time. Many units allow reading material made of cotton paper, or have an in-chamber TV. Electronic devices are typically not permitted.
The day of your session: what happens hour by hour
The full appointment takes 90 to 120 minutes from arrival to departure. Sessions are usually scheduled at the same time each weekday for the duration of your course to give your body a predictable rhythm.
- Arrival and briefing (10 to 15 minutes): You arrive at the hyperbaric unit, change into approved cotton clothing if needed, and receive a brief safety reminder from the chamber operator. A blood-glucose check is performed if you have diabetes (HBOT can cause transient hypoglycaemia in some patients). Vital signs may be taken.
- Compression (10 to 15 minutes): You enter the chamber and the chamber pressure increases gradually from surface (1 atmosphere) to your target treatment pressure of 2.0 to 2.4 ATA. The most common physical sensation during compression is increased pressure in the ears, similar to descending in an aeroplane or diving underwater. You equalise the same way: swallow, yawn, or perform a gentle Valsalva manoeuvre (pinch your nose and gently exhale against closed lips). If pressure does not equalise, signal the operator and they will pause or slow the compression.
- Treatment at depth (60 to 90 minutes): Once at target pressure, you breathe 100% oxygen continuously through a mask, hood, or directly from the chamber atmosphere depending on the chamber type. Most patients spend this time reading, dozing, listening to audio piped into the chamber, or watching TV through a chamber-side display. Some protocols include scheduled air breaks every 20 to 30 minutes to reduce the risk of oxygen toxicity; during an air break you remove the oxygen mask and breathe chamber air for 5 minutes.
- Decompression (10 to 15 minutes): Pressure returns to surface gradually. Your ears may pop again on the way back up. Some patients feel mildly tired or report temporary near-sightedness, which usually resolves over hours to days after the full course ends.
- Discharge: A final check from the unit nurse, a wound dressing change or other clinical task if needed, and you leave. Most patients drive themselves home immediately. Plan for 15 to 30 minutes of buffer after the session for any post-chamber clinical care.
Monoplace vs multiplace chambers: what’s the difference?
Canadian HBOT facilities operate two main chamber types. A monoplace chamber is a single-occupant clear acrylic tube. The chamber itself is pressurised with 100% oxygen, so the patient breathes the chamber atmosphere directly without a mask. Monoplace chambers are common at private clinics and some hospital programmes; they are simpler to operate and have a lower equipment footprint.
A multiplace chamber is a larger steel chamber that holds multiple patients and a chamber attendant at the same time. It is pressurised with compressed air; patients breathe 100% oxygen through individual masks or hoods. Multiplace chambers are standard at hospital-based programmes because they allow critical-care patients to be accompanied by a respiratory therapist, nurse, or physician during treatment, and they are required for emergency indications such as gas embolism and decompression sickness.
From the patient experience perspective, monoplace chambers can feel more confining (closed clear tube, slightly louder oxygen flow inside the chamber). Multiplace chambers feel more like a small room and allow conversation with the attendant or other patients. Treatment effectiveness is equivalent if pressure and breathing-gas protocols match.
Managing claustrophobia and chamber anxiety
Mild claustrophobia is one of the most commonly reported HBOT side effects, particularly during the first 2 to 3 sessions. Most patients adapt quickly. The acrylic monoplace chamber is fully transparent, you can see the operator and family members through the chamber wall the entire time, and you maintain two-way voice communication. The first session is often the most difficult; sustained reluctance usually resolves by session 3 to 5.
If you have a known history of significant claustrophobia or panic disorder, raise this with the hyperbaric medicine physician at your pre-screening. Strategies include a low-dose anxiolytic (such as a benzodiazepine) before the first few sessions, a multiplace chamber if available locally, or a brief in-chamber familiarisation visit before treatment begins. Some Canadian centres also have noise-cancelling headphones and guided meditation audio available during sessions.
Common side effects and what to do about them
| Side effect | Frequency | What to do |
|---|---|---|
| Ear pressure or barotrauma | Very common (the most common reason sessions are paused) | Equalise during compression with swallowing, yawning, or gentle Valsalva. If you cannot equalise, signal the operator. Pseudoephedrine or nasal decongestant before session can help if approved by your physician. |
| Temporary near-sightedness | Common in courses of 20+ sessions | Resolves over weeks after the course ends. Avoid getting new prescription glasses during treatment. |
| Mild fatigue | Common, especially in the first week | Plan a quiet afternoon after each session. Stay well hydrated. |
| Sinus pressure | Common with active sinus or cold | Consider postponing sessions if you have an active upper respiratory infection. Nasal decongestants may help if approved. |
| Anxiety or claustrophobia | ~5 to 10% of patients in the first 2 sessions | Discuss anxiolytic options at pre-screening. Most cases resolve by session 3 to 5. |
| Oxygen toxicity (CNS or pulmonary) | Rare at clinical protocols (under 0.01% of sessions) | Air breaks during the session are the standard prevention. Notify the operator immediately if you experience visual changes, facial twitching, or nausea. |
| Hypoglycaemia in diabetic patients | Possible in insulin-dependent diabetics | Blood glucose check before each session. Adjust insulin and timing with your endocrinologist. |
Course length and treatment rhythm
Most indications require a daily Monday-to-Friday schedule for the duration of the treatment course. Weekend breaks are standard. Specific course lengths vary by indication:
- Emergency indications (carbon monoxide poisoning, decompression sickness, gas embolism, severe crush injury): 1 to 5 sessions immediately, often delivered at higher pressure (2.5 to 2.8 ATA) with US Navy treatment tables.
- Problem wounds and diabetic foot ulcers: 20 to 40 daily sessions at 2.0 to 2.4 ATA, with progress reviews every 10 sessions.
- Late effects of radiation (radionecrosis, radiation cystitis, osteoradionecrosis): 30 to 60 daily sessions at 2.0 to 2.4 ATA, sometimes with pre-procedural prophylaxis blocks before dental extractions.
- Necrotising soft-tissue infections: typically delivered twice daily for the first 48 hours then once daily, in conjunction with surgical debridement and antibiotics.
- Sudden sensorineural hearing loss: 10 to 20 sessions, ideally started within 2 weeks of symptom onset.
- Refractory osteomyelitis: 20 to 40 sessions, often combined with bone biopsy-directed antibiotics.
If you are travelling for treatment and the schedule allows, some hospital programmes will let you return home on weekends to break up the trip. Confirm in advance with the hyperbaric unit because some emergency or twice-daily protocols cannot pause.
Who cannot have HBOT? Contraindications
The only absolute contraindication to HBOT is untreated pneumothorax (a collapsed lung that has not been drained). Compression in a chamber will rapidly enlarge any gas pocket trapped between the lung and chest wall, which can be life-threatening. This is why a chest X-ray is the standard pre-screening test.
Relative contraindications, where benefit must be weighed against risk by the hyperbaric medicine physician, include severe untreated emphysema with bullae, recent thoracic or ear surgery, active high-grade malignancy at the treatment site, congenital spherocytosis (severe), pregnancy in some indications (HBOT is used safely for severe maternal carbon monoxide poisoning where untreated CO is more dangerous), and certain chemotherapy or radiation-sensitising drugs that require a treatment pause. Discuss any current medications and recent procedures with the hyperbaric team before your first session.
Frequently Asked Questions
Can I drive home immediately after each session?
Most patients can drive themselves home. The exception is the first few sessions if you have significant claustrophobia and have taken an anxiolytic medication; in that case arrange a driver. If you experience pronounced visual changes from temporary near-sightedness, arrange a driver until the symptom stabilises.
How long until I notice a benefit?
It depends entirely on the indication. Emergency treatments (carbon monoxide poisoning, decompression sickness) typically produce symptom relief during the first session. Wound healing usually shows visible improvement around session 10 to 15. Late-radiation indications may take 20+ sessions before measurable change. Discuss expected timelines with your hyperbaric physician at the start of the course.
What happens if I miss a session?
Missing one or two sessions across a 40-session course is generally clinically acceptable. Missing more than 3 consecutive sessions can reduce the cumulative therapeutic effect, particularly for wound healing where dissolved-oxygen tension at the wound bed is the key driver. If you have to miss treatment for illness, travel, or any reason, notify the unit so they can adjust the schedule.
Can I exercise on the same day as HBOT?
Light activity is fine and is encouraged. Avoid heavy weightlifting, scuba diving, or flying within 12 hours of a session. Scuba diving within 12 hours of HBOT is specifically discouraged because it can precipitate decompression sickness.
Can I bring my phone or laptop into the chamber?
Personal electronic devices are typically not permitted because of fire and battery-safety concerns in a pressurised oxygen environment. Most units provide in-chamber entertainment (TV, audio piped in). Cotton-paper reading material is generally allowed. Confirm specifics with your chamber operator.
What does an HBOT session feel like?
The dominant physical sensation is the pressure change in your ears during compression and decompression, similar to descending in an aeroplane. At depth (during the treatment phase) most patients report no unusual sensation; they read, watch TV, or rest. The chamber air gets slightly warmer during compression and slightly cooler during decompression. Air through the oxygen mask is dry; many patients keep a sip of water nearby (cotton-cup, not plastic).
Related resources on Canada Hyperbarics
- Conditions treated with HBOT: the 14 Health Canada-recognised indications and the clinical evidence behind each.
- Facilities directory: interactive map of 33 Canadian HBOT facilities by city and province.
- HBOT coverage by province: provincial public insurance, extended benefits, auto insurance, WSIB / WCB, and Veterans Affairs Canada.
- Canadian medical travel guide: travel grants, interprovincial billing, hospital lodges, and tax deductibility for patients travelling for HBOT.
- FAQ: 79 patient-facing questions about treatment, safety, billing, and access.
Medical disclaimer: This page is for informational purposes only and is not medical advice. Specific clinical guidance must come from a hyperbaric medicine physician familiar with your case. For emergency hyperbaric indications such as carbon monoxide poisoning or decompression sickness, call 911 immediately.