TL;DR: Hyperbaric oxygen therapy (HBOT) is the only definitive treatment for acute decompression sickness (DCS) and arterial gas embolism (AGE). The 2024-2026 evidence base reinforces three clinical priorities for Canadian referring physicians: recognize neurological and inner-ear presentations early, deliver high-flow oxygen immediately while organizing transport to a recompression-capable chamber, and screen survivors for patent foramen ovale and dysbaric sequelae after recovery. This evidence review summarizes recent systematic reviews and case series and outlines the Canadian referral pathway.
Decompression sickness is a clinical syndrome caused by inert gas bubble formation following a rapid reduction in ambient pressure, most commonly after scuba diving but increasingly recognised in breath-hold diving, high-altitude exposure, and iatrogenic contexts. For Canadian referring physicians, recognizing DCS early and routing patients to recompression therapy without delay remains the single most important clinical decision. Recent evidence from 2024 through 2026 has refined our understanding of who recovers fully, who develops residual deficits, and how to monitor patients during and after hyperbaric treatment. This review distills that evidence for clinicians who may see DCS once or twice a career, and who need to act decisively when they do.
What is decompression sickness?
Decompression sickness is a clinical syndrome caused by inert gas bubbles forming in tissue or the bloodstream when ambient pressure drops faster than dissolved gas can be exhaled. The condition was traditionally divided into Type 1 (musculoskeletal pain, cutaneous, lymphatic) and Type 2 (neurological, cardiopulmonary, inner-ear, or vestibular). Modern hyperbaric practice often groups DCS and arterial gas embolism together under the broader heading of decompression illness (DCI), since both are managed with rapid recompression. Presentations range from joint pain (the “bends”) and mottled skin (cutis marmorata) through vestibular dysfunction, paraparesis, cerebral deficits, and cardiovascular collapse.
Inert gas bubble mechanics dominate the textbook description, but contemporary work increasingly emphasizes microparticle release, endothelial dysfunction, and downstream inflammation as parallel mechanisms in severe DCS. This matters clinically: it explains why some patients present with neurological deficits out of proportion to the apparent dive profile, why repeated HBOT sessions sometimes produce stepwise rather than abrupt recovery, and why follow-up monitoring (including autonomic and vestibular assessment) remains important after the chamber sessions are complete.
Why is hyperbaric oxygen the standard treatment?
HBOT works on three fronts in DCS: it reduces bubble volume through Boyle’s law, accelerates inert gas washout by maximizing the diffusion gradient, and improves tissue oxygenation in regions made ischaemic by bubble obstruction or endothelial injury. The United States Navy treatment tables remain the standard protocol references worldwide. Treatment Tables 5 and 6 use an initial pressure equivalent to 60 feet of seawater, approximately 2.82 ATA, while Treatment Table 6A starts at 165 feet (6.0 ATA) and is reserved for severe arterial gas embolism cases. A 2026 case in the Medical Journal, Armed Forces India describes complete recovery in a 28-year-old novice scuba diver who developed sudden complete visual loss while ascending from 18 metres, following two sessions on USN Treatment Table 6A for arterial gas embolism.
What does the 2024-2026 evidence show on treatment outcomes?
The largest contemporary outcomes dataset comes from a 2026 retrospective study published in International Maritime Health covering 178 decompression illness patients across multiple Thai hyperbaric centres from January 2020 to December 2023. The headline finding: 73.6% of patients achieved complete resolution of symptoms, while 26.4% had residual symptoms. Traditional (fishermen) divers were at higher risk of residual symptoms after treatment (42%). Missing safety stops showed a significant univariate association with incomplete outcomes (OR 2.495, 95% CI 1.263 to 4.926, p=0.008). Spinal cord involvement was strongly related to incomplete outcomes (p=0.001). Strikingly, only 18.5% of patients received first-aid high-flow oxygen before reaching the hyperbaric chamber.
For inner ear DCS specifically, a 2026 systematic review in Diving and Hyperbaric Medicine screened 3,683 records and included 24 studies representing 539 cases of inner ear DCS. Mean age was 44, average in-water dive depth was 29 metres of seawater, and mean dive duration was 38 minutes. After HBOT, only 37% of divers had residual symptoms on discharge despite 68% still showing dysfunction on laboratory testing, and 74% had a right-sided lesion. The review noted that vestibular rehabilitation was underutilized and only 46% of divers went on to have patent foramen ovale (PFO) screening despite the well-established link between right-to-left shunts and inner-ear DCS. For referring physicians, the takeaway is that follow-up matters as much as the acute intervention: discharge from the chamber does not mean discharge from monitoring.
How is breath-hold and high-altitude DCS different?
DCS is no longer a SCUBA-only diagnosis. A 2026 comprehensive review in The American Journal of Medicine synthesized 85 records documenting more than 244 cases of breath-hold DCS across 75 years, including historical Taravana syndrome in Polynesian pearl divers and contemporary cases among Japanese Ama, Korean Haenyeo, recreational freedivers, instructors, and spear fishers. Unlike SCUBA-related DCS, breath-hold DCS predominantly manifests as cerebral symptoms that can mimic stroke or transient ischaemic attack, often presenting in young, healthy individuals. Key risk factors include inadequate surface intervals during repetitive shallow dives, deep dives exceeding 40 metres, rapid ascent rates, and patent foramen ovale. The authors emphasize that immediate high-flow oxygen and urgent hyperbaric oxygen therapy remain essential treatments, and warn that with freediving popularity growing globally (an estimated one million participants), the condition is underrecognized and underreported.
High-altitude diving carries its own risk. A 2026 case report from Lake Van documented a 54-year-old recreational male diver, performing his first ever dive, who descended to approximately 30 metres and ascended rapidly to the surface without a decompression stop. He developed sudden weakness in both legs and shortness of breath, aspirated water, and lost consciousness before being towed back to shore. After CPR, transfer to hospital, and high-flow oxygen by non-rebreather mask, he received a single hyperbaric oxygen treatment session for suspected DCS. The Lake Van case is clinically relevant to Canadian practice because Canada has multiple high-altitude diving sites in Alberta, British Columbia, and the Canadian Shield, and reduced barometric pressure at altitude shrinks the safe decompression envelope compared with sea-level dives.
When should referring physicians escalate urgently?
Any suspicion of DCS or arterial gas embolism warrants immediate consultation with a hyperbaric medicine specialist and the Divers Alert Network. AGE is particularly time-critical. A 2026 case in Air Medical Journal describes a healthy young woman who sustained asystolic cardiac arrest immediately after surfacing from a scuba dive and required 90 minutes of resuscitation to achieve return of spontaneous circulation. After ROSC she remained profoundly unstable, on multiple vasopressors, with refractory hypothermia and hypoxemia, and was diagnosed with arterial gas emboli. The only treatment for AGE is rapid hyperbaric oxygen therapy, but she was too acute to be cared for in any local hyperbaric chamber; the closest chamber that could accommodate her acuity was 440 miles away. The authors describe the clinical and logistical challenges of long-distance critical care transport in this scenario.
The immediate priorities for the referring physician are these: place the patient supine, deliver 100% oxygen by non-rebreather mask, secure intravenous fluids, contact a hyperbaric chamber and the Divers Alert Network (DAN) 24-hour emergency line at +1-919-684-9111 (collect calls accepted), and arrange transport with cabin altitude restrictions for air ambulance. Do not delay oxygen for diagnostic imaging. The Thai outcomes data referenced above suggests that pre-chamber oxygen is underdelivered, even in experienced diving regions; the same is likely true in Canadian emergency departments that may see one DCS case a decade.
What long-term sequelae warrant follow-up?
Discharge from the recompression chamber is not the end of the clinical story. Three follow-up domains deserve attention.
Patent foramen ovale (PFO) screening
A 2025 case report in Diving and Hyperbaric Medicine describes cutaneous decompression sickness in a 43-year-old commercial diver after a dive to 17 metres of seawater for 160 minutes breathing air, with transfer under pressure and oxygen breathed during decompression in a dry chamber. He had worked as a commercial diver for 16 years without previous problems. A bubble contrast transthoracic echocardiogram showed a large atrial right-to-left shunt; his persistent foramen ovale was closed using a transcatheter technique and he returned to commercial diving. The authors note that shunt-mediated decompression sickness has not been previously reported after a shallow air dive with oxygen breathed during decompression, broadening the case for PFO screening in any DCS event where conventional decompression failure cannot explain the clinical picture.
Dysbaric osteonecrosis
A 2026 Algerian case series in Undersea and Hyperbaric Medicine presents three professional divers with dysbaric osteonecrosis of the humeral head with varying degrees of severity, including one case of advanced osteonecrosis declared permanently unfit for diving, following Type 1 DCS in the same region treated with hyperbaric oxygen therapy. The authors describe a controversial but potentially important link between previous decompression sickness with musculoskeletal pain (Type 1 DCS) and later osteonecrosis, and recommend early magnetic resonance imaging evaluation of all DCS cases with musculoskeletal pain so that osteo-medullary damage can be detected before continued diving worsens it.
Cardiovascular and gastrointestinal complications
A 2025 case report in Frontiers in Physiology documented a 35-year-old recreational diver with neurological DCS whose neurological symptoms resolved with HBOT but who developed persistent bradycardia. Heart rate variability analysis during HBOT and over two 24-hour Holter recordings revealed a biphasic autonomic pattern: initial parasympathetic dominance followed by sympathetic tilt and desynchronization. The authors suggest that advanced nonlinear and dynamic HRV analysis can reveal regulatory disturbances not captured by traditional methods, supporting a role for autonomic monitoring after DCS. Separately, a 2025 surgical case report describes a 63-year-old male with a history of HBOT for DCS six years earlier who developed ischaemic colitis with bowel necrosis following a 55-metre dive, requiring emergency bowel resection and descending colostomy. Ischemic colitis should be considered a differential diagnosis in DCS patients presenting with abdominal symptoms.
How does the Canadian referral pathway work?
Canada delivers acute decompression care through a small number of hospital-based hyperbaric facilities, supplemented by selected private chambers that may participate in informal coverage arrangements. For acute decompression illness, public hospital hyperbaric units are the preferred destination because they can accept critically ill patients, deliver USN Treatment Table 6 or 6A protocols, and coordinate with critical care transport. The national directory of hospitals and regulated facilities lists current Canadian HBOT centres by province; referring physicians should bookmark the directory and confirm operational status before recommending a transfer.
The Divers Alert Network is the most reliable single point of contact for triage of a suspected DCS case. DAN maintains a 24-hour emergency hotline staffed by diving medicine specialists who can advise on transport altitude restrictions, identify the closest available recompression chamber, and coordinate with the receiving team. For elective consultations on diver fitness, post-DCS return to diving, or chronic dysbaric injury, referring physicians can also use the DAN medical information line during business hours.
How does DCS presentation map to first-line response?
| DCS presentation | Clinical findings | First-line response | Typical USN protocol |
|---|---|---|---|
| Type 1 musculoskeletal | Joint pain, cutis marmorata, lymphatic swelling | 100% oxygen, hydration, urgent HBOT consult | USN Treatment Table 5 or 6 |
| Type 2 neurological (spinal) | Paraesthesia, paraparesis, urinary retention | 100% oxygen, supine, urgent transport | USN Treatment Table 6 |
| Cerebral DCS | Aphasia, hemiparesis, altered consciousness | Resuscitation, 100% oxygen, immediate transfer | USN Treatment Table 6 (or 6A if AGE) |
| Inner ear DCS | Vertigo, hearing loss, tinnitus, nystagmus | HBOT consult, ENT review, PFO screening | USN Treatment Table 6 |
| Arterial gas embolism | Acute neurological collapse on or after ascent | Supine, 100% oxygen, immediate recompression | USN Treatment Table 6A |
| Cutaneous DCS with shunt suspected | Marbled skin, often shoulders or trunk | HBOT consult, screen for PFO | USN Treatment Table 5 or 6 |
Frequently asked questions from referring physicians
Is HBOT effective for DCS that presents more than 24 hours after the dive?
Yes. While the strongest outcomes occur with rapid recompression, delayed treatment remains beneficial and is the standard of care. The Thai outcomes cohort cited above achieved 73.6% complete symptom resolution across a mixed-delay population including traditional fishermen-divers who often presented late. Refer regardless of delay, especially in the presence of neurological or inner-ear findings.
Should every DCS patient be screened for patent foramen ovale?
Best-practice opinion increasingly favours PFO screening in any inner-ear DCS, cerebral DCS, cutaneous DCS, or DCS occurring after a dive profile that would not normally produce decompression failure. The 2026 inner ear DCS systematic review noted that only 46% of inner-ear DCS divers had PFO screening, which the authors flagged as a quality gap, and Wilmshurst’s 2025 case report documents shunt-mediated DCS after a shallow air dive that would not have triggered conventional decompression failure.
What pre-transport interventions matter most?
Three things: 100% oxygen by non-rebreather mask, intravenous crystalloid for hydration, and cabin altitude restrictions if air transport is used. Pre-transport oxygen is consistently underdelivered in international DCS cohorts (only 18.5% of patients in the Thai dataset received first-aid high-flow oxygen) and likely also in Canadian emergency departments that see DCS rarely.
Does Health Canada recognize DCS as an HBOT indication?
Yes. Decompression sickness is one of the small set of indications for which HBOT is an established standard of care across major regulatory and professional bodies, including the Undersea and Hyperbaric Medical Society (UHMS) and the Canadian Undersea and Hyperbaric Medical Association (CUHMA). There is no Health Canada barrier to referral for acute DCS, and the condition is part of the published list of approved emergency HBOT indications.
When should I suspect DCS or AGE in a non-diver?
Iatrogenic AGE is the most common non-diving scenario, and several 2025-2026 case reports describe cerebral or venous gas embolism after percutaneous lung biopsy, central venous catheter manipulation, and robot-assisted partial nephrectomy. Sudden neurological collapse during or shortly after any procedure that exposes vasculature to air should prompt rapid HBOT consultation alongside the usual resuscitation. The clinical principle is identical to diving AGE: supine positioning, 100% oxygen, and the earliest feasible recompression.
What about breath-hold or freediving patients?
Breath-hold DCS is real, and the clinical picture is dominated by cerebral symptoms that can mimic stroke or transient ischaemic attack. The American Journal of Medicine 2026 review of 244+ cases over 75 years urges high clinical suspicion in young, healthy freedivers presenting with focal neurological deficits, particularly after repetitive deep dives. Treat exactly as you would SCUBA-related DCS: high-flow oxygen, urgent HBOT, and consideration of PFO screening on recovery.
Key takeaways for the referring physician
- HBOT is the only definitive treatment for acute DCS and AGE. Time to recompression matters more than choice of protocol.
- About three quarters of treated DCI patients achieve complete recovery, but spinal cord involvement and missed safety stops predict residual deficits.
- Pre-transport 100% oxygen and supine positioning are foundational, underdelivered interventions.
- Inner ear DCS responds well to HBOT but warrants PFO screening, vestibular rehabilitation, and audiometric follow-up.
- Long-term sequelae include dysbaric osteonecrosis, autonomic dysregulation, and rarely ischaemic colitis. Do not assume all post-DCS pain is musculoskeletal.
- The Divers Alert Network 24-hour line (+1-919-684-9111, collect calls accepted) is the most reliable triage and routing resource for Canadian referring physicians.
How Canada Hyperbarics can help
Canada Hyperbarics maintains a national directory of hospitals and regulated facilities that deliver hyperbaric oxygen therapy across Canada, alongside an indexed research database of peer-reviewed HBOT studies. For referring physicians who see DCS cases rarely, having the facility directory and DAN hotline saved and accessible is the highest-leverage preparation possible. We also publish evidence reviews for decompression sickness and other approved HBOT indications, and a broader FAQ for clinicians and patients. External references on regulatory and professional standards are available from UHMS and CUHMA.
This content is for informational purposes only and does not constitute medical advice. Referring physicians should consult their clinical judgment, current Canadian Undersea and Hyperbaric Medical Association guidance, and the receiving hyperbaric facility’s clinical team when managing suspected decompression illness.