Asia
Hyperbaric
Centre
Who Is
This For?
This emergency protocol is for two groups, and the first cannot wait for a booking system.
Group 1 — Divers with suspected AGE: Anyone who develops neurological symptoms during ascent or within minutes of surfacing — especially after a rapid ascent, a missed stop, running low on air, or a panicked climb to the surface. Note: this can happen in shallow water. Lung over-expansion does not require depth [1] [2].
Group 2 — Iatrogenic (procedure-related) air embolism: Air entering the arterial circulation during or after a hospital procedure — central line placement or removal, cardiac or neurosurgical procedures, certain endovascular work. Hospitals manage the acute phase; we support the recompression decision with their team [3].
AGE is a clinical diagnosis made on the dive history and the symptoms — not on scans. Waiting for imaging costs the brain time it does not have [1] [2]. If AGE is on the table, the right sequence is oxygen, call, recompress — assess in parallel, never in series.
Now. Of all the conditions on this site, this one has the sharpest clock: outcomes are best when recompression begins within two hours, remain favourable within six, and decline meaningfully beyond that — though recovery has been documented well beyond 24 hours and nobody should self-exclude [2] [4].
Act immediately if:
A diver loses consciousness, seizes, becomes confused, or develops weakness, numbness, vision loss, or speech problems during ascent or within minutes of surfacing.
Anyone develops stroke-like symptoms during or immediately after a medical procedure involving vascular access.
Symptoms appeared hours ago and you are unsure whether it is still worth acting. It is. The evidence includes recoveries after delays of a day and more — let the assessment decide, not the clock [4] [5].
One myth, retired: the head-down position is no longer recommended during transport. High-flow 100% oxygen, lying flat, rapid coordination with us or emergency services — that is the modern first aid [1] [2].
When to Consider HBOT
Pressure Against the Bubble
An arterial gas embolism is physics first and biology second. During ascent, air in the lungs expands. If it cannot escape — a held breath, a blocked airway, a panicked climb — it ruptures the delicate air sacs and forces bubbles into the pulmonary veins, the heart, and onward to the brain [1].
Recompression answers with two levers, and both are immediate.
First, Boyle's Law. Take the chamber to 2.8 ATA and the bubble's volume falls by nearly two-thirds. A bubble blocking a cerebral artery shrinks enough for blood to pass, and enough for the vessel to begin clearing it [1] [4].
Second — and modern research suggests this may matter even more — hyperbaric oxygen attacks the injury the bubble leaves behind. Bubbles pass through vessels in minutes, but they injure the vessel lining on the way, triggering inflammation and brain swelling that outlasts the bubble itself. Oxygen under pressure counters all three: it constricts healthy vessels to reduce oedema without starving tissue, it down-regulates the inflammatory cascade, and it floods threatened brain tissue with dissolved oxygen while circulation recovers [1] [2].
That is why normobaric oxygen is first aid but never the finish: symptoms that settle on surface oxygen commonly relapse without recompression [2].
The Science & Clinical Evidence
We do not make promises. The record does that.
There are no randomized trials of recompression for AGE — withholding the definitive treatment from someone with a bubble in their cerebral circulation is unthinkable. What exists is a large, consistent body of case literature and outcome reviews, and it points one direction [4].
The most comprehensive review gathered 656 published AGE cases and compared those who received hyperbaric oxygen with those who did not [4]:
78% vs 56% — full recovery with recompression versus without. — Dutka, reviewed by Moon, Undersea & Hyperbaric Medicine, 2019 [4]
5% vs 42% — mortality with recompression versus without. This is the starkest number on any page on this site, and it is why AGE is a Class I indication: recompression is not optional, it is the treatment. — Dutka, reviewed by Moon, 2019 [4]
Timing governs the outcome more than any other factor. Consensus guidance and case series agree: most people recompressed within two hours achieve favourable outcomes; within six hours, improvement remains frequent; beyond that, odds decline — but recoveries after 24 hours and longer are documented [2] [4] [5].
Where we are honest with you: outcomes are not uniform. Severe presentations — deep coma, cardiac involvement — carry the hardest odds, and published series of iatrogenic cases show roughly four in ten complete recovery with another third partial [3]. Very rarely, a case needs deeper pressure capability than our 3.0 ATA maximum (a US Navy Table 6A excursion); the modern evidence suggests this is seldom necessary because bubbles transit the vasculature quickly — but when it is needed, we stabilise and coordinate transfer, and we tell you so [2] [4].
Recompression follows established US Navy treatment tables — the worldwide standard for diving medicine [4] [6]. Specifics are set by case severity and the supervising specialist.
Primary protocol: US Navy Treatment Table 6 — 2.8 ATA with 99.5% medical-grade oxygen and scheduled air breaks, approximately 4 hours 45 minutes [6].
Chamber capability: Up to 3.0 ATA — covering the standard table. Cases requiring deeper tables are stabilised and transferred by coordination [4].
Oxygen Purity: 99.5% Medical-Grade Oxygen — pharmaceutical-grade purity certified under the Pharmacy and Poisons Ordinance (Cap. 138) [7].
Follow-up sessions: Residual symptoms are treated with additional sessions (typically 90 minutes at 2.0–2.5 ATA) — AGE commonly needs several before resolution is complete [2] [4].
First aid before you reach us: High-flow 100% oxygen, lie flat, isotonic fluids if available, no flying. Call first — we guide you through it [1] [2].
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 before recovery?
Many people improve noticeably during the first recompression — but AGE typically needs more than one session. Published guidance and series report several treatments (often three to five or more) before resolution is complete, followed by shorter follow-up sessions for residual symptoms [2] [4]. The neurological review after each session decides the next step.
It has been more than two hours. Should we still come?
Yes. Two hours is the ideal, not the deadline. Improvement remains frequent within six hours, and complete recoveries are documented after delays of 24 hours and longer [2] [4] [5]. The review of 656 cases found full recovery in 78% overall — many of those were not treated within two hours [4]. Call. Let the assessment decide.
I felt better after breathing oxygen at the dive site. Do I still need recompression?
Yes — and this is one of the most dangerous assumptions in diving. Surface oxygen relieves symptoms without removing the cause; relapse without recompression is well documented, and the second hit lands on already-injured vessels [2]. Feeling better is good. It is not the finish. The published position is unambiguous: recompression is required even after apparent recovery [2] [4].
UHMS. Air or Gas Embolism. UHMS Hyperbaric Oxygen Therapy Indications, 15th Edition. Undersea and Hyperbaric Medical Society. UHMS Official Indications
StatPearls. Diving Gas Embolism. NCBI Bookshelf, 2025. NBK482321
Benson J, Adkinson C, Collier R. Hyperbaric oxygen therapy of iatrogenic cerebral arterial gas embolism. Undersea Hyperb Med. 2003;30:117-126.
Moon RE. Hyperbaric treatment of air or gas embolism: current recommendations (including the Dutka 656-case review). Undersea Hyperb Med. 2019;46(5). UHMS
Covington D, Bielawski A, Sadler C, Latham E. A favorable outcome despite a 39-hour treatment delay for arterial gas embolism: case report. Undersea Hyperb Med. 2016;43(4):457-461.
US Navy Diving Manual — Treatment Table 6 (2.8 ATA oxygen recompression protocol). Commander, Naval Sea Systems Command.
Hong Kong e-Legislation. Pharmacy and Poisons Ordinance (Cap. 138). Cap. 138 on e-Legislation
