What is the typical duration of hyperbaric oxygen therapy (HBOT) for a patient with carbon monoxide poisoning?

Duration of Hyperbaric Oxygen Therapy for Carbon Monoxide Poisoning

For acute carbon monoxide poisoning, the optimal hyperbaric oxygen (HBO2) treatment protocol consists of 3 sessions within 24 hours: an initial session at 3.0 ATA for 60 minutes followed by 2.0 ATA for 65 minutes, then two additional sessions at 2.0 ATA for 90 minutes at pressure (120 minutes total chamber time). 1

Evidence-Based Treatment Protocol

Standard HBO2 Regimen

The most robust evidence comes from the Weaver 2002 study, which demonstrated significant reduction in cognitive sequelae using the following protocol: 1

• First session: 3.0 ATA for 1 hour, followed by 2.0 ATA for 1 hour
• Second and third sessions: 2.0 ATA for 90 minutes at pressure (within 24 hours of initial treatment)
• Outcome: 21% absolute reduction in neurologic sequelae at 6 weeks (46% vs 25%; NNT=5), with benefits persisting to 12 months 1

Alternative Single-Session Protocol

If multiple sessions are not feasible, a single HBO2 session can be administered: 1

• Protocol: 2.8 ATA for 30 minutes followed by 2.0 ATA for 90 minutes
• Evidence: Thom study showed 23% absolute reduction in neurologic sequelae (NNT=4.3) 1
• Limitation: This study excluded patients with loss of consciousness and only included those presenting within 6 hours 1

Timing Considerations

Critical timing window: HBO2 should ideally be initiated within 6 hours of CO exposure, as beneficial effects may diminish significantly with delays beyond this timeframe. 1 However, treatment can still be considered up to 24 hours post-exposure based on the Weaver protocol. 1

When HBO2 is Not Available: Normobaric Oxygen

If hyperbaric oxygen is unavailable, administer 100% normobaric oxygen for approximately 6 hours until: 1

• COHb normalizes (<3%)
• Patient's presenting symptoms resolve
• Rationale: 100% normobaric oxygen reduces COHb half-life to approximately 74 minutes (compared to 320 minutes on room air) 1

Pressure and Duration Variations in Studies

Different studies have used varying protocols, which may explain conflicting results: 1

• 2.0 ATA protocols: Used in studies showing no benefit (Raphael, Annane) 1
• 2.5-2.9 ATA protocols: Used in studies with mixed or positive results 1
• 3.0 ATA initial session: Used only in the Weaver study showing strongest benefit 1

Multiple Session Protocols

Studies examining extended treatment courses: 1

• Scheinkestel protocol: 3-6 daily HBO2 sessions at 2.8 ATA showed no benefit and possibly worse outcomes (74% poor outcomes in HBO2 vs 68% in controls) 1
• Recent evidence: A 2023 randomized trial found no difference between one versus three HBO2 sessions (50% vs 55% neuropsychological sequelae at 6 weeks), though both groups had higher sequelae rates than earlier studies 2

Critical Caveats

Avoid rapid correction: When initiating any oxygen therapy in patients with chronic hypercapnia or severe poisoning, avoid rapid normalization of blood gases, as this can worsen cerebral perfusion. 3

Suboptimal dosing concerns: Studies using 2.0 ATA pressure may have employed suboptimal HBO2 doses, potentially explaining negative results. 1 The higher initial pressure (3.0 ATA) in the Weaver protocol may be crucial for efficacy.

Patient selection matters: The benefit of HBO2 appears most pronounced in patients with loss of consciousness, prolonged exposure (≥24 hours), age ≥36 years, or COHb ≥25%, though no single criterion is 100% predictive. 1