Asia
Hyperbaric
Centre
Who Is
This For?
This urgent protocol is for people exposed to carbon monoxide within roughly the last 24 hours — the window in which the evidence is strongest [1]. Common sources in Hong Kong include faulty gas water heaters, fires and smoke inhalation, blocked flues, generators, and charcoal burned in enclosed spaces.
It is most strongly indicated when any of the following apply:
You lost consciousness, even briefly, during the exposure.
You have ongoing symptoms now: headache, nausea, dizziness, confusion, chest pain, or difficulty concentrating.
Your blood carboxyhaemoglobin level was elevated at hospital.
You are pregnant — carbon monoxide crosses to the foetus, which clears it more slowly than you do [4].
The exposure was severe or prolonged, even if you feel recovered now.
A doctor's referral is required — typically from the emergency physician who assessed you. If you have just left hospital after a CO exposure, call us first and we will coordinate directly.
Within 24 hours of exposure. That is the window used in the pivotal randomized trial, and the sooner inside it, the better [1].
Act now if:
You were assessed at hospital for carbon monoxide exposure within the last day — whether or not you received oxygen there.
You feel fine now but the exposure was significant. This is exactly the scenario the delayed-injury data addresses: feeling recovered is not the same as being safe [1] [5].
Anyone in your household was exposed at the same time. They need assessment too, whether or not they have symptoms.
If more than 24 hours have passed, the evidence is thinner but the decision is still worth a conversation — contact us and your physician, and we will give you a straight answer about whether a session is likely to help [1].
When to Consider HBOT
Two Problems. Pressure Answers Both.
Carbon monoxide attacks in two stages, and understanding both explains why pressure — not just oxygen — matters.
Stage one is displacement. Carbon monoxide binds to your red blood cells roughly 240 times more tightly than oxygen, physically blocking oxygen transport. Time clears it — slowly. Breathing normal air, the half-life is four to six hours. Breathing pure oxygen at normal pressure, about 90 minutes. At 2.5 to 3.0 ATA in the chamber, 20 to 30 minutes [2] [3]. Pressure does not just speed the washout; it dissolves enough oxygen directly into your plasma to keep tissue alive while the carbon monoxide leaves [1].
Stage two is quieter, and more dangerous. Even after blood levels normalise, carbon monoxide triggers an inflammatory cascade in the brain — white blood cells adhere to cerebral blood vessel walls and begin damaging neural tissue through lipid peroxidation. This is the mechanism behind delayed neurological injury, and laboratory research shows that hyperbaric oxygen — but not oxygen at normal pressure — interrupts it [3].
That is the case for pressure in one sentence: oxygen alone clears the gas faster; oxygen under pressure clears it fastest and protects the brain from what comes next [1] [3].
The Science & Clinical Evidence
We do not make promises. The research does that — and this page carries both the strongest randomized trial in emergency hyperbaric medicine and an honest account of the debate around it.
The pivotal trial, published in the New England Journal of Medicine, randomised 152 people with acute CO poisoning to three sessions of hyperbaric oxygen or oxygen at normal pressure, all within 24 hours of exposure [1]:
25% vs 46% — the incidence of delayed cognitive injury at six weeks with hyperbaric oxygen versus oxygen alone. The benefit persisted at six months and at one year. In practical terms: for roughly every five people treated under pressure, one case of delayed brain injury was prevented. — Weaver et al., New England Journal of Medicine, 2002 [1]
An earlier randomized trial found the same pattern for delayed neurological symptoms specifically [5]:
0% vs 23% — the incidence of delayed neurological sequelae with hyperbaric oxygen versus oxygen alone. — Thom et al., 1995 [5]
The physics is unambiguous and was established decades ago [2]:
20–30 minutes — the half-life of carbon monoxide in your blood under hyperbaric oxygen, versus about 90 minutes on pure oxygen at normal pressure and 4 to 6 hours breathing air. — Pace et al., Science, 1950 [2]
Where we are honest with you: this indication is genuinely debated. A Cochrane review pooling six trials did not reach statistical significance overall (odds ratio 0.78; confidence interval crossing 1) [6], and researchers have raised fair methodological criticisms of the Weaver trial — including baseline imbalances between its groups [7]. Major hyperbaric and emergency medicine bodies nonetheless continue to recommend hyperbaric oxygen for significant CO poisoning, and the mechanism evidence for the pressure component is strong [1] [3] [4]. Our position matches the evidence: for significant exposure within 24 hours, the risk-benefit balance clearly favours treatment. We will tell you if your case does not fit that description.
Our protocol follows the structure used in the pivotal randomized trial [1]. In this emergency, timing outranks everything else.
First session: As soon as possible after hospital assessment — within 24 hours of exposure [1].
Chamber Pressure: Up to 3.0 ATA for the initial session (our chamber's full capability), with subsequent sessions at 2.0–2.5 ATA [1] [8].
Oxygen Purity: 99.5% Medical-Grade Oxygen — pharmaceutical-grade purity certified under the Pharmacy and Poisons Ordinance (Cap. 138) [9].
Session Duration: 90 minutes at depth.
Total Course: Typically 1 to 3 sessions, per the trial protocol and your physician's assessment [1].
The Protocol
What To Expect
We understand that entering a hyperbaric chamber can feel unfamiliar. Our team is here to guide you through every step of the process, ensuring you feel comfortable, safe, and supported.
Step 1 — The Briefing & Preparation: Before your first session, our technician will walk you through the safety protocols. You will change into 100% cotton clothing (provided) to eliminate static risk. No electronics, watches, or oil-based cosmetics are allowed inside the chamber.
Step 2 — Pressurisation: As the chamber pressurises over 10-15 minutes, you will feel a sensation in your ears similar to descending in an airplane. Our technician will coach you on simple techniques to clear your ears. Once at depth (2.0-2.4 ATA), you will breathe 99.5% pure oxygen through a comfortable hood or mask. You can read, rest, or watch a screen during the 90-minute session.
Step 3 — Depressurisation & Next Steps: The chamber will slowly depressurise over 10-15 minutes. Once open, you can return to your normal daily activities immediately. Our technician will examine your wound site and coordinate with your primary wound care team to track your progress.
FAQ
How many sessions will I need?
Far fewer than for our other protocols — typically one to three, based on the randomized trial structure and your physician's assessment [1]. The first session is the critical one, and it should happen within 24 hours of exposure.
I feel completely fine now. Do I still need this?
That is precisely the question the delayed-injury data answers. In the largest trial, nearly half of those treated with oxygen alone developed memory, concentration, or cognitive problems in the following weeks — many of them after feeling recovered [1]. Feeling fine is good news. It is not a clearance. If your exposure was significant and you are within the window, the evidence supports coming in.
Is hyperbaric oxygen the settled standard for CO poisoning?
It is the recommended treatment of the UHMS and widely used internationally for significant exposure — and it is also honestly debated, because a Cochrane review pooling all trials did not reach statistical significance [4] [6]. The strongest single trial showed a clear benefit [1]; the physics is undisputed [2] [3]. We give you all of that, plainly, and the decision is made with your physician — never under pressure from us. The only pressure involved is in the chamber.
Weaver LK, et al. Hyperbaric oxygen for acute carbon monoxide poisoning. N Engl J Med. 2002;347(14):1057-1067. PubMed 12362009
Pace N, Strajman E, Walker EL. Acceleration of carbon monoxide elimination in man by high pressure oxygen. Science. 1950;111(2877):652-654. PubMed 15422575
Thom SR, et al. Delayed neuropsychologic sequelae after carbon monoxide poisoning: prevention by treatment with hyperbaric oxygen (leukocyte adhesion and lipid peroxidation mechanism studies). Am J Physiol Heart Circ Physiol. 2004;287(4):H1800-H1806. PubMed 15205179
UHMS. Carbon Monoxide Poisoning. UHMS Hyperbaric Oxygen Therapy Indications, 15th Edition. Undersea and Hyperbaric Medical Society. UHMS Official Indications
Thom SR, Taber RL, Mendiguren II, et al. Delayed neuropsychologic sequelae after carbon monoxide poisoning: prevention by treatment with hyperbaric oxygen. Ann Emerg Med. 1995;25(4):474-480. [UNVERIFIED — volume/pages to be confirmed before publication]
Buckley NA, et al. Hyperbaric oxygen for carbon monoxide poisoning. Cochrane Database of Systematic Reviews. 2011;(4):CD002041. [UNVERIFIED — exact issue number to be confirmed before publication]
Buckley NA, et al. Commentary: hyperbaric oxygen should not be used routinely for carbon monoxide poisoning. Br J Clin Pharmacol. 2022. Wiley
NHS England. Evidence review: hyperbaric oxygen therapy for carbon monoxide poisoning. NHS England Evidence Review
Hong Kong e-Legislation. Pharmacy and Poisons Ordinance (Cap. 138). Cap. 138 on e-Legislation
