Your first hyperbaric oxygen therapy session can feel unfamiliar — a sealed pressurized tube, mandated cotton gowns, and ear-popping pressure changes are not a typical medical experience.
Knowing the protocol in advance turns the unfamiliar into the routine. This guide walks through what happens before, during, and after a first session at a UHMS-accredited center.
Before Your Session
Medical Consultation
Every legitimate HBOT center requires a medical evaluation before treatment. The UHMS Clinical Hyperbaric Facility Accreditation Manual (2023) requires the following workup.
The intake covers:
- Health history: chronic conditions, recent surgeries, current medications, allergies
- Contraindication screening: untreated pneumothorax is the only absolute contraindication per StatPearls HBOT Contraindications (2024); uncontrolled asthma, severe COPD, recent thoracic surgery, and active chemotherapy with bleomycin or doxorubicin are relative contraindications
- Ear assessment: ability to equalize, history of ear surgery, current ETD or middle ear effusion
- Treatment plan discussion: protocol pressure, number of sessions, indication category (on-label vs off-label), realistic outcome expectations
- Informed consent: signed acknowledgment of risks including barotrauma, oxygen toxicity, and reversible myopic shift
If the clinic skips the medical intake — particularly common at wellness clinics offering mild HBOT for off-label conditions — that's a red flag.
The FDA Safety Communication (2021, reaffirmed 2024) explicitly warns against facilities offering HBOT without proper medical screening for non-cleared indications.
What to Wear
The FDA documented 27 chamber fire events between 1923 and 2018 in the 2021 Safe Use of HBOT Devices letter. Every single one involved an ignition source carried into an oxygen-enriched environment.
Dress accordingly:
- 100% cotton clothing — required by virtually every UHMS-accredited facility
- No synthetic fabrics — nylon, polyester, fleece, and spandex generate static electricity
- No metal jewelry — watches, rings, necklaces, piercings must come off
- No electronics — phones, tablets, smartwatches, hearing aids, vapes stay outside
- No cosmetics — no makeup, hair products, lotions, oil-based moisturizers, or nail polish containing acetone
- Most centers provide hospital-style cotton gowns and slippers
Hair should be clean and free of styling product. Some centers require removing contact lenses; check with your facility.
Ear Equalization Practice
Ear equalization is the single most important comfort skill. The Divers Alert Network technique guide (2023) outlines four methods worth practicing in the days before your session.
- Swallowing — the simplest method, often sufficient for slow pressurization rates
- Jaw movement — opening, closing, and shifting your jaw side to side
- Valsalva maneuver — pinch your nose closed, close your mouth, gently blow until your ears pop
- Frenzel maneuver — close your throat, pinch your nose, push the tongue against the roof of your mouth
Do not use forceful Valsalva — it can cause middle-ear barotrauma. The American Academy of Otolaryngology guidelines (2024) emphasize gentle, continuous equalization throughout pressure changes.
If you cannot equalize, alert the technician immediately. They can slow the pressurization rate or pause descent.
What to Eat and Drink
A light meal 1-2 hours before treatment is ideal — chamber sessions are long enough to be uncomfortable on an empty stomach but heavy meals can cause reflux at pressure.
Hydrate well. Some facilities recommend extra water intake the day before, particularly for longer protocols.
Avoid alcohol for 24 hours before treatment. Carbonated drinks immediately before can cause gas discomfort during compression. Caffeine in moderation is fine.
Avoid smoking before and during your protocol course — the CDC tobacco fact sheet (2024) documents how nicotine causes vasoconstriction, which directly undermines the tissue-oxygen delivery HBOT is trying to enhance.
During Your Session
Chamber Entry
Staff will orient you to the chamber controls, the intercom or phone system, and the emergency procedures.
The two chamber types feel different:
- Monoplace chambers — you lie down inside a clear acrylic tube about 7 feet long, breathing the chamber atmosphere
- Multiplace chambers — you sit or recline in a room-sized steel chamber with other patients, breathing 100% oxygen through a mask or hood
Communication runs through an intercom or hardwired phone. Staff monitor you continuously through the chamber wall or interior video.
Pressurization (5-15 minutes)
Chamber pressure gradually increases to treatment level — typically 2.0-2.5 ATA for the on-label conditions described in the UHMS 13th Edition Indications (2024).
What you'll feel: ear fullness similar to descending in an airplane. Air temperature rises a few degrees due to compression.
What to do: equalize continuously using the techniques you practiced. Don't wait for discomfort.
If ear pain occurs: alert staff immediately. They can slow or pause pressurization to give you time to equalize.
Forcing pressurization through pain is the most common cause of middle-ear barotrauma, the most frequent HBOT side effect documented across clinical literature (StatPearls, 2024).
Treatment Phase (60-90 minutes)
You breathe 100% oxygen at full treatment pressure. Henry's Law dictates how dissolved plasma oxygen rises — at 2.0 ATA on pure oxygen, dissolved oxygen increases roughly 15-fold over breathing room air at sea level.
What you'll feel: nothing unusual. Breathing feels normal.
What to do: relax, rest, sleep, watch in-chamber TV (available at many centers), or listen to music.
Air breaks: longer protocols include 5-minute air breaks every 20-30 minutes to reduce oxygen toxicity risk per the Cochrane Oxygen Toxicity review (2023).
Depressurization (5-15 minutes)
Chamber pressure gradually returns to normal atmospheric pressure.
What you'll feel: ear popping similar to airplane ascent. Air cools slightly.
What to do: equalize gently — this phase is usually easier than pressurization. Don't hold your breath; breathe normally throughout.
After Your Session
Immediate Post-Session
No significant downtime is required. Most patients drive themselves home and resume normal activities the same day.
Some patients feel energized; others feel mild fatigue, particularly in the first few sessions. The 2025 Scientific Reports long COVID trial noted improved sleep quality emerging within the first 10-15 sessions for many participants.
Mild ear fullness may persist for 30-60 minutes. Drink extra water.
Common Post-Session Experiences
- Energized feeling — frequently reported, particularly after the first few sessions
- Mild fatigue — common in early sessions, often improves with each subsequent treatment
- Better sleep — frequently reported across long COVID, PTSD, and TBI study populations
- Increased appetite — modest, often reported in the first week
- Transient myopic shift — temporary near-sightedness developing over 20-40 sessions, reversing within 6-8 weeks of treatment completion per StatPearls HBOT Side Effects (2024)
Rare but Documented Side Effects
- Middle-ear barotrauma — the most common HBOT complication, usually mild
- Sinus squeeze — particularly if you have an active cold or allergies
- Confinement anxiety — manageable with monoplace chambers having clear walls or with mild pre-treatment anxiolytics
- Oxygen toxicity seizure — rare at 2.0-2.4 ATA protocols, more concerning at 2.8+ ATA, mitigated with air breaks
- Pulmonary oxygen toxicity — only with very long or repeated daily protocols
Frequently Asked Questions
Does HBOT hurt?
No. HBOT itself is painless. The only discomfort is ear pressure during pressurization, which is managed with the equalization techniques covered above. If equalization is difficult, staff slow the pressurization rate. Most patients find the experience relaxing once they get comfortable with ear clearing. The UHMS Patient Information sheets (2024) describe pain as "uncommon when proper equalization is maintained.". See the multiple sclerosis evidence atlas for the full investigational evidence breakdown.
Can I bring my phone into the chamber?
No. Electronic devices are not permitted inside hyperbaric chambers per the FDA Safety Communication (2021) because battery-powered devices in oxygen-enriched environments are a documented ignition source. Many monoplace chambers have built-in entertainment systems. Multiplace chambers may have shared screens.
What if I feel claustrophobic?
Monoplace chambers are transparent acrylic, letting you see the room around you. If claustrophobia concerns are significant, ask your facility about clear-wall chambers, communication systems, the option of pre-treatment anxiolytics prescribed by your physician, or multiplace chambers that feel more like a room. The Cleveland Clinic Hyperbaric Medicine Patient FAQ (2024) notes that most patients adapt within 2-3 sessions. See why major medical centers stay silent on HBOT for the full institutional-silence analysis.
How will I know HBOT is working?
Response varies by indication and individual. Many patients notice improved energy and sleep within the first 5-10 sessions. Cognitive improvements may appear after 15-20 sessions. Wound healing is assessed by your physician at regular intervals. Full benefits typically manifest by the end of a 40-session protocol — the standard course used in the 2025 Scientific Reports long COVID trial and the 2024 Frontiers in Neurology PTSD systematic review.
Can I stop treatment early if I feel better?
You may feel improvement before completing the prescribed protocol, but stopping early may produce suboptimal outcomes. The 2025 long COVID study used 40 full sessions and benefits were cumulative. The Cochrane diabetic foot ulcer review (2024) similarly showed dose-dependent healing rates. Discuss any desire to modify your protocol with your physician rather than stopping independently.
Find HBOT Centers Near You
Browse our complete directory of UHMS-accredited HBOT centers to find a verified facility near you and schedule your initial consultation.
-- The HBOT Finder Team
Medical Disclaimer: This article is for informational purposes only and does not constitute medical advice. HBOT should be administered under physician supervision at a UHMS-accredited facility for the 14 conditions recognized by UHMS HBO Indications 13th Edition (2024). Off-label use carries no regulatory clearance and is not covered by insurance.
Editorial Disclosure: HBOT Finder maintains editorial independence. We do not accept paid placements in our directory.