Hyperbaric oxygen therapy is the definitive emergency treatment for moderate-to-severe carbon monoxide poisoning. It accelerates carboxyhemoglobin elimination from minutes rather than hours and reduces the rate of delayed neurological sequelae compared to normobaric oxygen alone. CO poisoning is recognised by Health Canada as one of the 14 conditions for which provincial health insurance covers HBOT, and emergency treatment is delivered at all Canadian hospital-based hyperbaric programmes.
Quick Answer
Does HBOT help carbon monoxide poisoning? Hyperbaric oxygen therapy is the definitive emergency treatment for moderate-to-severe carbon monoxide poisoning. It accelerates carboxyhemoglobin elimination from minutes rather than hours and reduces the rate of delayed neurological sequelae compared to normobaric oxygen alone. CO poisoning is recognised by Health Canada as one of the 14 conditions for which provincial health insurance covers HBOT, and emergency treatment is delivered at all Canadian hospital-based hyperbaric programmes.
Carbon monoxide (CO) is a colourless, odourless gas produced by incomplete combustion of carbon-containing fuels. The most common Canadian sources are furnaces and water heaters with cracked heat exchangers or blocked exhaust, gas-powered generators run indoors during ice-storm power outages, vehicle exhaust in attached garages, charcoal grills brought indoors, propane heaters in poorly ventilated cabins or ice-fishing huts, and house or apartment fires. Public Health Agency data attribute roughly 200 to 300 unintentional CO-related deaths and several thousand emergency-department presentations across Canada each year, with cluster spikes during winter cold snaps and after major weather events.
The pathophysiology is multi-system. CO binds hemoglobin with 200 to 250 times the affinity of oxygen, forming carboxyhemoglobin (COHb) that cannot transport oxygen and that distorts the remaining hemoglobin's oxygen-release curve, worsening tissue hypoxia. CO also binds intracellular cytochrome c oxidase, blocking mitochondrial respiration even where oxygen is available, and binds myoglobin in cardiac and skeletal muscle, contributing to ischemic injury. After the acute exposure ends, CO triggers an inflammatory cascade in brain endothelium, with neutrophil adhesion, lipid peroxidation, and an autoimmune-like response to myelin basic protein that drives the syndrome of delayed neurological sequelae.
Clinical presentation ranges from headache, dizziness, and nausea (often misdiagnosed as flu) at COHb levels of 10 to 20 percent, through confusion, syncope, and chest pain at 20 to 40 percent, to seizures, coma, and cardiac arrhythmia above 40 percent. Symptom severity correlates poorly with COHb level once exposure has ended, because COHb is already declining by the time the patient reaches hospital. Loss of consciousness, even briefly, is the most reliable predictor of severe poisoning regardless of the measured COHb. Pregnant patients are at particular risk because fetal hemoglobin has even higher CO affinity than adult hemoglobin and the fetus's COHb level can exceed the mother's by 10 to 15 percent, with delayed clearance.
Hyperbaric oxygen therapy attacks CO poisoning along three independent mechanisms, each of which contributes to the rationale for treatment beyond what normobaric oxygen alone can achieve. The first and most quantifiable is acceleration of CO elimination from hemoglobin. The half-life of COHb on room air is approximately 320 minutes, falls to approximately 74 minutes on 100 percent oxygen at 1 ATA via a non-rebreather mask, and falls further to approximately 23 minutes at 2.8 ATA on 100 percent oxygen in the chamber. Faster elimination shortens the period of tissue hypoxia and limits cumulative ischemic injury.
The second mechanism is the dissolution of oxygen directly into plasma. At 2.8 ATA on 100 percent oxygen, plasma oxygen content rises to approximately 6 mL of oxygen per 100 mL of plasma, enough to meet the body's basic metabolic oxygen demand even with hemoglobin substantially blocked by CO. This restores aerobic metabolism in the brain and myocardium during the treatment session and limits secondary ischemic injury until the carboxyhemoglobin clears. The high tissue partial pressure of oxygen also displaces CO from cytochrome c oxidase, restoring mitochondrial function.
The third mechanism is anti-inflammatory and is the basis for HBOT's effect on delayed neurological sequelae. Hyperbaric oxygen blocks the adhesion of activated neutrophils to brain microvascular endothelium, preventing the cascade of neutrophil-mediated injury that contributes to white-matter demyelination and basal-ganglia damage in the days to weeks after exposure. It reduces lipid peroxidation in the brain, attenuates the immune response to oxidatively modified myelin basic protein, and supports endogenous antioxidant systems including superoxide dismutase and catalase. These effects underlie the cognitive-protection signal seen in the Weaver et al. RCT and several smaller randomised trials.
Typical Treatment Protocol
Emergency hyperbaric treatment is delivered at 2.8 to 3.0 ATA for 90 to 150 minutes per session. The most widely used Canadian protocols are the Weaver protocol (3.0 ATA for 60 minutes followed by 2.0 ATA for 60 minutes, with brief air breaks to limit oxygen toxicity) and the US Navy Treatment Table 6, originally designed for decompression sickness but commonly applied to severe CO poisoning. Most patients receive one to three sessions over the first 24 to 48 hours, with the total number guided by clinical response, persistent symptoms, and the treating hyperbaric physician's judgement. Pregnant patients with confirmed CO exposure typically receive at least one session regardless of maternal symptoms because of the prolonged fetal COHb half-life. Throughout pre-treatment work-up, the receiving emergency department keeps the patient on 100 percent oxygen via non-rebreather mask, draws an arterial or venous blood gas with co-oximetry to confirm COHb level, obtains a 12-lead ECG and troponin to screen for cardiac injury, and checks neurological status with a standardised cognitive screening tool to establish a baseline for follow-up.
Level A - Strong Evidence
Supported by high-quality RCTs and systematic reviews
The Weaver et al. RCT (NEJM 2002, 152 patients with acute symptomatic CO poisoning) showed cognitive sequelae at 6 weeks in 25 percent of HBOT-treated patients versus 46 percent of patients receiving normobaric oxygen, with the benefit persisting at 12 months. This trial established HBOT as the standard of care for moderate-to-severe CO poisoning and is the most-cited piece of evidence in current Canadian guidelines.
Carboxyhemoglobin half-life falls from approximately 320 minutes on room air to 74 minutes on 100 percent normobaric oxygen and to approximately 23 minutes at 2.8 ATA on hyperbaric oxygen, supporting the principle that HBOT is faster (and arguably more complete) than non-hyperbaric oxygen for CO elimination.
A Cochrane Review (Buckley et al. 2011, updated 2018, 7 RCTs and 1361 participants) found a non-significant trend toward reduced delayed neurological sequelae with HBOT but noted substantial methodological heterogeneity across the trials. The Weaver protocol with early treatment is the most consistent positive signal across the evidence base.
Loss of consciousness during exposure, even briefly, is the strongest single clinical predictor of risk for delayed neurological sequelae in published cohorts. Many Canadian programmes use any documented loss of consciousness as an automatic indication for HBOT, regardless of measured COHb.
In pregnancy, several case series and one observational study (Elkharrat et al. 1991) suggest HBOT reduces fetal mortality and neurological sequelae compared to normobaric oxygen alone, although no randomised trials exist. Canadian and US pregnancy guidelines recommend HBOT for any pregnant patient with confirmed CO exposure and symptoms, or COHb above 15 to 20 percent.
Cardiac injury (troponin elevation, ECG changes, arrhythmia) occurs in approximately 30 to 40 percent of moderate-to-severe CO poisoning cases and is associated with worse long-term outcomes. Cardiac biomarker screening is now standard in Canadian emergency-department protocols for confirmed CO exposure.
Highest-evidence-tier studies tagged to this condition in the Canada Hyperbarics research database, ranked by evidence tier (1 = meta-analysis or RCT, 2 = cohort, 3 = case series), most recent first.
Acute Med Surg · 2026 · Meta-Analysis
J Korean Med Sci · 2025 · Meta-Analysis
J Clin Neurosci · 2024 · Meta-Analysis
Healthcare (Basel) · 2022 · Meta-Analysis
Zhonghua Lao Dong Wei Sheng Zhi Ye Bing Za Zhi · 2018 · RCT
Studies in our database that include a ClinicalTrials.gov registration. Trial registration is a marker of methodological rigour because the protocol, primary outcome, and analysis plan are deposited before enrolment begins.
Critical care medicine · 2021 · Retrospective Study · PMID 34074856
Scandinavian journal of trauma, resuscitation and emergency medicine · 2010 · Clinical Study · PMID 20550698
Most patients arrive at hospital by ambulance after a 911 call from the exposure scene, often a household where multiple occupants are symptomatic at once. The receiving emergency department places you on 100 percent oxygen by non-rebreather mask immediately, draws blood for carboxyhemoglobin co-oximetry (a standard arterial or venous blood gas with the co-oximetry option), and screens for cardiac involvement with an ECG and troponin. If your COHb level, symptoms, or exposure history meet hyperbaric criteria, the ED physician contacts the on-call hyperbaric medicine team. In Ontario, this typically involves a CritiCall Ontario referral on 1-800-668-4357. In other provinces the call goes directly to the receiving hospital chamber. Transport to the chamber facility, when needed, is arranged through provincial critical-care transport services.
The first hyperbaric session begins as soon as the chamber is ready, usually within one to four hours of ED arrival. You change into cotton scrubs (no synthetics, lotions, or jewellery) and enter the chamber. Pressurisation takes five to ten minutes and feels like an aircraft descent, with ear-clearing maneuvers as needed. During the treatment phase you breathe pure oxygen by mask or hood while the chamber holds at 2.8 to 3.0 ATA, with one or two brief air-breaks to reduce oxygen toxicity risk. You are monitored continuously for level of consciousness, oxygen saturation, and ECG. Decompression takes another five to ten minutes. The total time inside is typically 90 to 150 minutes.
After the first session, you are usually admitted for observation, with repeat neurological assessment and further sessions in the next 24 to 48 hours as clinically indicated. Most patients have a follow-up neuropsychological assessment scheduled at four to six weeks to screen for delayed neurological sequelae, which can present as memory problems, mood changes, headaches, or movement disorders weeks after the apparent acute recovery. Pregnant patients have additional fetal monitoring during and after each session. Recovery for non-severe cases is usually full within days to weeks; severe cases may have residual cognitive or movement deficits even with prompt treatment.
Carbon monoxide poisoning is treated as an emergency at all 11 Canadian hospital-based hyperbaric programmes and is fully covered by every provincial health-insurance plan. The standard escalation pathway begins at the local emergency department, where the patient is stabilised on 100 percent normobaric oxygen and assessed for hyperbaric criteria. The receiving ED then arranges transport to the nearest chamber.
In Ontario, CritiCall Ontario at 1-800-668-4357 is the single coordination line that connects emergency departments to the three hospital programmes (Toronto General / UHN, Hamilton General Hospital, The Ottawa Hospital). CritiCall maintains 24/7 awareness of which chambers are operational and accepting emergencies, and arranges Ornge air or land critical-care transport when needed. Treatment is fully covered by OHIP without prior authorisation.
In British Columbia, emergencies route to Vancouver General Hospital's Leon Judah Blackmore Pavilion, the only hospital hyperbaric chamber in the province. BC ambulance critical-care transport handles cases from outside the Lower Mainland; treatment is fully covered under MSP. In Alberta, emergencies route to Misericordia Community Hospital in Edmonton (Covenant Health) or the Foothills Medical Centre / Arthur J.E. Child Comprehensive Cancer Centre in Calgary (Alberta Health Services). The Alberta hospital billing code for HBOT detention time is 13.99I (per 15 minutes); emergency treatment is fully covered without prior authorisation. In Quebec, RAMQ covers treatment at Hôpital du Sacré-Cœur de Montréal and Hôtel-Dieu de Lévis. Nova Scotia (MSI), Newfoundland and Labrador (MCP), and Saskatchewan also cover hospital-delivered emergency CO treatment, with caveats around current chamber availability in Saskatchewan since the 2021 Wigmore Hospital staffing disruption.
For patients in provinces or territories without a local hyperbaric chamber (Manitoba, New Brunswick, Prince Edward Island, Yukon, Northwest Territories, Nunavut), inter-provincial referral by air ambulance to the nearest hospital chamber is the standard. The most common destinations are Misericordia Edmonton (for prairie and territorial patients) and the Ontario hospital programmes. The Divers Alert Network 24/7 emergency consultation line at 1-919-684-9111 is also available to Canadian emergency departments and can help locate the nearest accepting chamber when local pathways fail.
Hyperbaric oxygen therapy for the 14 Health Canada-recognised conditions, including Carbon Monoxide Poisoning, is delivered at the 11 hospital hyperbaric programmes located in seven provinces (Ontario, Quebec, British Columbia, Alberta, Nova Scotia, Newfoundland and Labrador, and Saskatchewan). The six provinces and territories without an in-province hospital programme (Manitoba, New Brunswick, Prince Edward Island, Yukon, Northwest Territories, and Nunavut) route patients to the nearest receiving hospital programme. Use the links below for province-specific coverage, referral pathway, and emergency routing details.
Hospital + Private
OHIP (Ontario Health Insurance Plan)
Hospital Only
MSP (Medical Services Plan)
Hospital + Private
Alberta Health / AHCIP
Hospital Only
RAMQ
Disrupted
Saskatchewan Health Authority
No Hospital Chamber
Manitoba Health
Hospital Only
MSI (Medical Services Insurance)
No Hospital Chamber
Medicare NB
Hospital Only
MCP (Medical Care Plan)
Out-of-Province Referral
Health PEI
Out-of-Province Referral
Yukon Health and Social Services
Out-of-Province Referral
NWT Health and Social Services
Out-of-Province Referral
Nunavut Department of Health
For acute or emergency presentations of Carbon Monoxide Poisoning, call 911 first. The receiving emergency department coordinates urgent transfer to the nearest hospital hyperbaric programme through the relevant provincial transfer network (CritiCall Ontario at 1-800-668-4357, BC Patient Transfer Network, EHS Nova Scotia, or equivalent). For diving-related emergencies, the Divers Alert Network (DAN) emergency hotline is 1-919-684-9111.
Untreated pneumothorax is the only absolute contraindication, because trapped intrathoracic air expands on decompression. The pneumothorax must be drained with a chest tube before chamber entry. In the emergency setting, severe relative contraindications are weighed pragmatically against the risk of permanent neurological injury from untreated CO poisoning. Concurrent treatment with bleomycin (oxygen-induced pulmonary fibrosis risk) and disulfiram (interference with antioxidant defences) are formally contraindicated but rarely encountered in acute CO presentations. Pregnancy is not a contraindication; it is in fact a strong indication, because fetal hemoglobin has even higher CO affinity than adult hemoglobin and the fetal COHb half-life is several times longer than the maternal value. Treatment thresholds for pregnant patients are correspondingly lower (any significant maternal exposure with confirmed COHb above 15 percent, or any maternal symptoms regardless of level). Children with confirmed CO exposure are also treated more aggressively because of higher metabolic rates and greater vulnerability to delayed sequelae.
HBOT is indicated for any patient with confirmed CO exposure plus one or more of the following: loss of consciousness (even briefly) at any point during or after exposure, neurological symptoms (confusion, focal deficit, seizure), cardiac involvement (chest pain, troponin elevation, ECG ischemia), pregnancy, age under 18, or measured carboxyhemoglobin above 25 percent (lower thresholds for pregnant patients, children, and patients with cardiac comorbidity). Most Canadian centres also treat any persistent symptoms after four to six hours of normobaric oxygen.
One to three sessions is typical, delivered over the first 24 to 48 hours. The Weaver protocol uses three sessions in the first 24 hours; many Canadian programmes deliver one or two and reassess based on clinical response. Persistent neurological symptoms after the first session are the most common reason to add additional treatments.
Yes. CO poisoning is an emergency hyperbaric oxygen indication covered by every provincial health-insurance plan (OHIP, MSP, Alberta Health, RAMQ, MSI, MCP, Saskatchewan, and the territorial programmes via inter-provincial referral) at all 11 hospital-based hyperbaric programmes. No prior authorisation is required for emergency treatment.
It can reduce the risk. The Weaver et al. 2002 NEJM RCT showed HBOT cut the rate of cognitive sequelae approximately in half at six weeks and twelve months compared to normobaric oxygen alone. The benefit is most pronounced in patients treated within six hours of exposure who had loss of consciousness or cardiac involvement.
As soon as feasible, ideally within six hours of removal from the CO source. The benefit declines but does not disappear with delay; treatment within 24 hours is still considered clinically worthwhile in most Canadian protocols, especially for patients with persistent neurological symptoms.
A non-rebreather mask delivers approximately 70 to 90 percent oxygen at 1 atmosphere of pressure (sea level). It cuts the carboxyhemoglobin half-life from about 320 minutes on room air to about 74 minutes. Hyperbaric oxygen at 2.8 atmospheres delivers 100 percent oxygen at much higher pressure, cuts the COHb half-life to about 23 minutes, dissolves enough oxygen directly into plasma to meet basic metabolic demand independent of hemoglobin, and adds an anti-inflammatory effect on brain endothelium that normobaric oxygen does not provide.
If symptoms have resolved, you have no loss of consciousness, no cardiac symptoms, you are not pregnant, and a measured COHb is below the threshold (often 15 to 25 percent depending on programme), normobaric 100 percent oxygen for several hours is usually adequate. Even mild exposures should be evaluated in an emergency department because some delayed neurological sequelae can present without dramatic acute symptoms. Removing yourself from the source and seeking medical assessment is always the first step.
Fetal hemoglobin has even higher CO affinity than adult hemoglobin, and the fetal carboxyhemoglobin level can exceed the maternal level by 10 to 15 percent with a much longer elimination half-life. Maternal HBOT is generally recommended for any pregnant patient with confirmed CO exposure plus symptoms, or COHb above 15 to 20 percent, regardless of how the mother feels. HBOT itself is considered safe in pregnancy at the pressures used for CO poisoning. Fetal monitoring is included in the treatment plan.
Delayed neurological sequelae (DNS) is a syndrome of cognitive, mood, and movement symptoms that develops days to weeks after apparent recovery from acute CO poisoning. It can include memory problems, difficulty concentrating, irritability or depression, headache, parkinsonian movement disorders, and (rarely) more severe neurocognitive decline. DNS occurs in approximately 15 to 40 percent of moderate-to-severe poisonings without HBOT, and is the main reason hyperbaric treatment is recommended for symptomatic patients even when the acute COHb has cleared.
Tell the team the time the alarm sounded, when you left the source, what you were doing during the exposure, and any symptoms you noticed. Bring anyone else who was in the same space; they may also have absorbed CO and need assessment. The emergency department will measure COHb, screen for cardiac and neurological involvement, and decide on treatment based on the combination of exposure history, symptoms, and lab results, not just the COHb number alone.
Most Canadian programmes schedule a follow-up visit at four to six weeks for cognitive screening using a standardised neuropsychological tool. Patients with cardiac involvement also have repeat cardiology assessment. If new symptoms develop after discharge (memory problems, movement issues, mood changes), patients are encouraged to return because additional HBOT sessions can sometimes reverse delayed sequelae caught early.
You change into cotton scrubs, enter the chamber, and lie down (in a monoplace) or sit in a recliner (in a multiplace with multiple patients). Pressurisation takes five to ten minutes and feels like the descent in an aircraft, with ear-clearing as in flying. During the 90 to 150 minute treatment phase you breathe pure oxygen through a mask or hood. Decompression takes another five to ten minutes. Most patients describe the sensation as warm and quiet. You are continuously monitored for level of consciousness and oxygen saturation.
Working CO alarms on every level of the house and outside each sleeping area are the single most effective preventive measure and are required by code in most Canadian provinces. Annual servicing of furnaces, water heaters, and any fuel-burning appliances by a licensed technician catches the cracked heat exchangers and blocked vents that cause most household CO incidents. Never run a generator, gas-powered tool, or charcoal grill indoors or in an attached garage, even with the door open. If your CO alarm sounds, leave the house immediately and call 911 from outside.
CO poisoning is treated as an emergency at all 11 Canadian hospital hyperbaric programmes. The Canada Hyperbarics verified directory at canadahyperbarics.ca/facilities/ lists all programmes with phone numbers, addresses, and current operational status. In an emergency, the local emergency department will arrange the referral; in Ontario, this is coordinated through CritiCall Ontario at 1-800-668-4357.