Overview
HBOT is UHMS-approved for severe carbon monoxide poisoning, defined by loss of consciousness, cardiovascular compromise, severe metabolic acidosis, or CO level >25%. The Weaver et al. 2002 NEJM trial demonstrated significant reduction in cognitive sequelae at 6 weeks and 12 months versus normobaric oxygen.
Carbon monoxide (CO) is a colourless, odourless gas that binds haemoglobin with 200+ times the affinity of oxygen, forming carboxyhaemoglobin (COHb) and reducing oxygen delivery. Severe acute CO poisoning causes loss of consciousness, cardiac ischaemia, and death. A proportion of survivors develop delayed neurological sequelae — cognitive dysfunction, personality changes, parkinsonism — weeks to months after apparent recovery.
The Weaver et al. 2002 double-blind RCT (NEJM) is the foundational trial. 152 patients with symptomatic CO poisoning were randomised to three HBOT sessions (first at 3.0 ATA, subsequent at 2.0 ATA) or normobaric oxygen. At 6-week and 12-month follow-up, the HBOT group had significantly lower rates of cognitive sequelae. The protocol — now called the Weaver protocol — is the clinical standard for acute CO HBOT.
Indication criteria for HBOT in CO poisoning: loss of consciousness (even brief), neurological symptoms, cardiac ischaemia, severe metabolic acidosis, pregnancy, or COHb level >25%. Mild CO poisoning without these features is typically managed with normobaric oxygen alone.
How HBOT Works for This Condition
HBOT accelerates CO displacement from haemoglobin by elevating dissolved plasma oxygen and competing CO off haemoglobin binding sites. The CO half-life drops from ~5 hours on room air to ~20 minutes at 3.0 ATA with 100% oxygen. Beyond COHb clearance, HBOT reduces leukocyte-mediated reperfusion injury implicated in delayed neurological sequelae.
GRADE Evidence Rating
Weaver 2002 NEJM RCT + 6-year follow-up establish mortality/morbidity benefit. Weaver protocol is standard of care.
| GRADE Domain | Assessment |
|---|---|
| Risk of bias | Low |
| Consistency | Consistent |
| Directness | Direct |
| Precision | Precise |
GRADE methodology: Grading of Recommendations Assessment, Development and Evaluation. See GRADE Working Group.
Clinical Protocol
| Typical protocol | 1–3 sessions at 2.5–3.0 ATA, 90 minutes each (Weaver protocol) |
|---|---|
| Evidence level | Strong (RCT) — UHMS approved |
| FDA status | FDA-approved indication |
Weaver protocol: first session at 3.0 ATA for 60 minutes with air breaks, two subsequent sessions at 2.0 ATA for 60 minutes with air breaks, all within the first 24 hours. Pregnant patients and specific severe presentations may require additional sessions.
Evidence Base
Weaver 2002 NEJM is the methodologically strongest HBOT trial. UHMS Tier 1. Prior and subsequent trials (Scheinkestel 1999, Raphael 1989, Thom 1995) produced mixed results, variously attributed to differences in CO severity, treatment timing, and protocol specifications.
Cautions & Considerations
- Time-critical — initiate within hours of exposure for maximum benefit.
- Requires 24/7 hyperbaric facility access.
- Severe CO poisoning is often polyvictim (building fires, suicide attempts) — require coordinated emergency response.
- Pregnancy is a specific indication (CO poisoning in pregnancy threatens fetus disproportionately).
Key Research & References
- Weaver et al. 2002 (NEJM)
- UHMS Indications Manual
- Scheinkestel 1999 (mixed results)
Indexed Studies for This Condition
Linked entries in the HBOT Studies Database.
Frequently Asked Questions
When is HBOT indicated for CO poisoning?
For severe or symptomatic CO poisoning — loss of consciousness, neurological symptoms, cardiac ischaemia, severe acidosis, pregnancy, or COHb >25%. Mild cases are managed with normobaric oxygen alone.
How quickly must HBOT be given?
As quickly as possible. The Weaver trial required initiation within 24 hours. Earlier is better. Three sessions typically delivered within the first 24 hours.
Does HBOT prevent delayed neurological sequelae?
The Weaver 2002 trial showed significant reduction in cognitive sequelae at 6 weeks and 12 months with HBOT vs normobaric oxygen alone. Prevention is not complete, but risk is substantially reduced.
Research disclaimer: This article summarises published research for educational purposes only. Nothing here is medical advice. HBOT is a prescription medical treatment that must be administered under physician supervision in appropriately certified chambers. Discuss any treatment decisions with a qualified clinician.