The American College of Emergency Physicians has released updated clinical guidelines on the use of normobaric oxygen therapy in adult patients with acute carbon monoxide poisoning. The Level C recommendation remains unchanged, supporting selective HBO₂ use based on symptom severity and treatment availability.
The guidelines were released following the results of a systematic review evaluating long-term neurocognitive outcomes. The review identified four new qualifying studies since American College of Emergency Physicians' (ACEP) 2017 guidelines, including one retrospective study and three meta-analyses. All newly included studies were graded as Class III evidence, and no new Class I or II studies were identified, reinforcing the continued uncertainty regarding hyperbaric oxygen therapy’s (HBO₂) long-term efficacy.
“In symptomatic carbon monoxide (CO) poisoning, selected patients may benefit from hyperbaric oxygen (HBO₂) treatment based on severity of symptoms and availability (distance and time),” stated the Level C recommendation, which reflected recommendations based on Class III evidence or expert consensus.
In a retrospective study involving 2,034 patients from a Japanese nationwide database, investigators suggested modest short-term benefits of HBO₂ therapy. The study found:
- Improved mental status (number needed to treat [NNT] = 42, difference = −3.2%, 95% confidence interval [CI] = −4.9% to −1.5%)
- Better activities of daily living (ADL) outcomes (NNT = 41, difference = −5.3%, 95% CI = −7.8% to −2.7%) compared with controls.
However, the study had significant limitations, including a lack of standardized HBO₂ protocols, absence of long-term follow-up beyond 7 days, and potential selection bias. Some treatment centers used as little as 2.0 ATA for only 60 minutes, making comparisons inconsistent across facilities.
Additionally, the included meta-analyses (Ho et al., Lin et al., Wang et al.) had methodological weaknesses primarily caused by lack of blinding in most studies, which increased the risk of bias in neurocognitive assessments.
ACEP highlighted major practical challenges in HBO₂ implementation, stating that “only a small proportion of these existing HBO₂ centers have the equipment and staff necessary to treat high-acuity patients.”
Additionally, long-distance transport remained a concern: “Transport for more than 50 miles for these patients may be needed from many areas of the [United States], with the additional risks accompanying travel and possible deterioration.”
The guidelines outlined several potential harms of HBO₂ therapy, including:
- Hyperbaric-induced middle ear barotrauma
- Oxygen toxicity (seizure risk)
- Risks and costs associated with transport
- Clinical deterioration during transport
- Need for significant (> 50 miles) travel
- Chamber-induced claustrophobia.
One study (Annane et al., 2011) suggested that multiple HBO₂ sessions may be associated with worse memory and concentration outcomes; however, this finding requires further investigation. These results indicated that additional HBO₂ treatments do not necessarily improve patient outcomes and may, in some cases, be detrimental.
ACEP acknowledged the ongoing controversy surrounding HBO₂ for CO poisoning and emphasized the need for further research in the following areas:
- Optimal timing of HBO₂ therapy
- Defining patient selection criteria
- Standardized HBO₂ treatment protocols
- Long-term follow-up on neurocognitive outcomes.
CO poisoning remains a significant global health issue, with:
- More than 1 million cases reported worldwide annually
- Nearly 50,000 emergency department visits annually in the United States.
The updated ACEP guidelines maintain a Level C recommendation for HBO₂ in selected patients with symptomatic CO poisoning. However, because of the continued uncertainty regarding its long-term neurocognitive benefits, high logistical burdens, and potential risks, HBO₂ therapy remains a selective option rather than a standard of care.