Physician Referral Guide: Hyperbaric Oxygen for Carbon Monoxide Poisoning

Assessing the patient before referral

While arranging hyperbaric assessment, the receiving emergency department should:

• Place the patient on 100 percent oxygen by non-rebreather mask immediately and continue it through transport.
• Draw an arterial or venous blood gas with co-oximetry to confirm the COHb level.
• Obtain a 12-lead ECG and troponin. Cardiac injury occurs in roughly 30 to 40 percent of moderate-to-severe cases and predicts worse outcomes.
• Document a baseline neurological and cognitive status with a standardised screening tool, so later delayed-sequelae assessment has a reference point.
• Record the exposure history: source, duration, loss of consciousness, and the number of other symptomatic people from the same environment.

What the evidence supports

The reference evidence is the Weaver et al. randomised controlled trial (NEJM 2002, 152 patients), which found cognitive sequelae at six weeks in 25 percent of hyperbaric-treated patients versus 46 percent of those receiving normobaric oxygen, with the benefit persisting at twelve months. This trial established hyperbaric oxygen as the standard of care for moderate-to-severe poisoning and remains the most-cited evidence in Canadian practice.

The mechanistic rationale is well established. COHb half-life falls from about 320 minutes on room air to about 74 minutes on 100 percent normobaric oxygen and to about 23 minutes at 2.8 ATA in the chamber. Beyond faster elimination, hyperbaric oxygen dissolves enough oxygen into plasma to sustain aerobic metabolism while haemoglobin is blocked, and it blunts the neutrophil-mediated inflammatory cascade that drives delayed neurological sequelae.

The evidence is not uniform. A Cochrane review (Buckley et al. 2011, 6 RCTs) found only a non-significant trend toward reduced delayed sequelae and noted substantial heterogeneity across trials. The most consistent positive signal is early treatment using the Weaver protocol. In pregnancy, no randomised trials exist, but case series and observational data support treatment for any confirmed exposure with symptoms.

The Canadian referral pathway

Carbon monoxide poisoning is treated as an emergency at all 11 Canadian hospital-based hyperbaric programmes and is covered by every provincial plan without prior authorisation.

• Ontario: call CritiCall Ontario at 1-800-668-4357, the single coordination line that connects emergency departments to the Toronto General (UHN), Hamilton General, and The Ottawa Hospital programmes and arranges Ornge transport when needed.
• British Columbia: route to Vancouver General Hospital (Leon Judah Blackmore Pavilion), the only hospital chamber in the province; covered under MSP.
• Alberta: route to Misericordia Community Hospital (Edmonton) or Foothills Medical Centre / Arthur J.E. Child Comprehensive Cancer Centre (Calgary); covered by Alberta Health.
• Quebec: RAMQ covers Hopital du Sacre-Coeur de Montreal and Hotel-Dieu de Levis.
• Provinces and territories without a hospital programme (Manitoba, New Brunswick, PEI, Yukon, NWT, Nunavut): inter-provincial air-ambulance referral to the nearest receiving hospital programme.

The Divers Alert Network 24/7 emergency line at 1-919-684-9111 can also help Canadian emergency departments locate the nearest accepting chamber when local pathways fail.

How to use the research list below

The list contains every carbon monoxide poisoning study in the Canada Hyperbarics database that was published in 2020 or later and has a freely available full-text version, each linked directly to that full text. Paywalled and abstract-only studies are excluded, and retracted studies are removed. This is a reference list, not a set of summaries. Counts and the open-access set refresh each quarter.