Clinical Indications for Hyperbaric Oxygen Therapy

The optimal selection of patients for HBOT remains an area of active clinical discussion, and treatment decisions should be individualized.

Hyperbaric consultation should be strongly considered when carbon monoxide poisoning is associated with findings such as:

• Loss of consciousness or syncope
• Persistent altered mental status
• Focal neurologic findings
• Seizure
• Significant cognitive or neuropsychiatric abnormalities
• Evidence of myocardial ischemia or other cardiac injury
• Hemodynamic instability
• Severe metabolic acidosis
• Substantial carbon monoxide exposure
• Persisting symptoms despite high-concentration oxygen
• Pregnancy

The Centers for Disease Control and Prevention advises consideration of HBOT when COHb exceeds approximately 25–30%, or when cardiac involvement, severe acidosis, unconsciousness, neurologic impairment, or abnormal neuropsychiatric testing is present.

HBOT may also be appropriate at lower COHb concentrations when the clinical presentation or exposure history suggests significant poisoning.

A COHb threshold should not be used as the sole criterion for referral.

Pregnancy and Carbon Monoxide Poisoning

Pregnancy requires particular consideration because carbon monoxide exposure can threaten both the pregnant patient and the fetus. The fetus is especially vulnerable to carbon monoxide toxicity, and maternal symptoms or COHb concentrations may not fully reflect fetal exposure or risk. Current CDC clinical guidance supports a more aggressive approach to hyperbaric treatment in pregnancy and identifies HBOT as the treatment of choice for pregnant patients with carbon monoxide poisoning, including patients who may appear less severely poisoned than nonpregnant adults. Suspected significant CO poisoning during pregnancy warrants prompt consultation with specialists experienced in toxicology, maternal-fetal care, and hyperbaric medicine.

Carbon Monoxide Poisoning Complicated by Cyanide Exposure

Carbon monoxide and cyanide toxicity may occur simultaneously in victims of smoke inhalation, particularly following structural fires. The combination can produce severe cellular hypoxia and cardiovascular toxicity. UHMS recognizes carbon monoxide poisoning complicated by cyanide poisoning within its accepted hyperbaric indications and recommends strong consideration of HBOT in these cases. HBOT does not replace appropriate cyanide antidotal therapy, airway management, burn care, or critical care. Treatment should be coordinated with emergency medicine, toxicology, critical care, and hyperbaric medicine specialists.

Timing of HBOT

When HBOT is indicated, treatment should generally be initiated as early as practical after stabilization. The potential benefit of hyperbaric treatment is not limited to rapid elimination of carboxyhemoglobin. The inflammatory and neurologic consequences of carbon monoxide exposure may continue after COHb concentrations have fallen substantially. For this reason, normalization of the COHb level does not necessarily eliminate the potential rationale for HBOT in a symptomatic patient. Transfer decisions should balance the potential benefit of hyperbaric treatment against the patient’s clinical stability, transport time, distance to an appropriate hyperbaric facility, and the facility’s ability to manage critically ill patients.

HBOT as Part of Emergency Medical Management

Hyperbaric oxygen therapy does not replace initial emergency treatment. Management of suspected or confirmed carbon monoxide poisoning begins with immediate removal from the exposure and administration of high-concentration oxygen.

Additional management may include:

• Airway and ventilatory support
• Serial neurologic assessment
• Electrocardiography
• Cardiac biomarker testing when indicated
• Hemodynamic support
• Evaluation for concomitant trauma or burns
• Assessment for smoke inhalation injury
• Evaluation and treatment of possible cyanide toxicity
• Pregnancy testing when applicable
• Critical care monitoring in severely poisoned patients

Patients should be medically stabilized to the extent possible before transport or hyperbaric treatment, particularly because management of an acutely deteriorating patient may be more complex within a hyperbaric chamber.

Delayed Neurologic Sequelae

One of the major concerns following carbon monoxide poisoning is the development of delayed neurologic or neuropsychiatric complications. A patient may initially improve and subsequently develop new symptoms days or weeks after the exposure. Potential delayed manifestations include:

• Memory impairment
• Difficulty concentrating
• Changes in executive function
• Personality or behavioral changes
• Depression or other psychiatric symptoms
• Gait abnormalities
• Movement disorders
• Parkinsonian features
• Headache
• Dizziness
• Balance disturbances
• Other cognitive or neurologic deficits

The possibility of delayed neurologic sequelae is one reason treatment decisions cannot be based solely on normalization of carboxyhemoglobin or resolution of immediate symptoms.

Patients discharged after carbon monoxide poisoning should receive appropriate follow-up instructions and should be advised to seek reevaluation if new neurologic, cognitive, or behavioral symptoms develop.

Clinical Evidence and Guidelines

Carbon monoxide poisoning is an accepted indication for Hyperbaric Oxygen Therapy according to the Undersea & Hyperbaric Medical Society.

UHMS states that HBOT should be considered for acute symptomatic carbon monoxide poisoning based on randomized clinical trials, experimental evidence, physiologic mechanisms, and accumulated clinical experience.

The evidence regarding which patients derive the greatest long-term neurologic benefit remains less definitive.

A landmark randomized, double-blind clinical trial published in the New England Journal of Medicine found that a three-treatment hyperbaric oxygen regimen reduced cognitive sequelae at six weeks and at later follow-up in patients with symptomatic acute carbon monoxide poisoning.

Other randomized trials have not demonstrated the same benefit, however, and differences in patient selection, treatment protocols, timing, outcome assessment, and study design have contributed to continuing debate.

The American College of Emergency Physicians reviewed the evidence again in its 2025 clinical policy. ACEP concluded that, in symptomatic acute carbon monoxide poisoning, selected patients may benefit from HBOT based on the severity of symptoms and treatment availability, including distance and time to a capable hyperbaric facility.

Accordingly, early consultation with a hyperbaric medicine specialist is particularly valuable in patients with significant poisoning because the decision can incorporate clinical severity, individual risk factors, available evidence, transport considerations, and local treatment capabilities.

Medicare Coverage

Acute carbon monoxide intoxication is specifically listed as a covered condition under the Centers for Medicare & Medicaid Services National Coverage Determination for Hyperbaric Oxygen Therapy (NCD 20.29).

Coverage recognition does not guarantee payment for an individual treatment. Applicable documentation, medical necessity, coding, facility, and payer-specific requirements should be reviewed.

When to Refer

Consider prompt hyperbaric medicine consultation for patients with acute carbon monoxide poisoning when there is:

• Loss of consciousness
• Significant or persistent neurologic dysfunction
• Altered mental status
• Seizure
• Cardiac ischemia or other evidence of myocardial injury
• Hemodynamic instability
• Severe metabolic acidosis
• Significant persistent symptoms following oxygen administration
• High-risk exposure circumstances
• Pregnancy

Do not delay consultation solely because the carboxyhemoglobin concentration has fallen or normalized after oxygen treatment.

Clinical severity and the circumstances of exposure are more informative than a single COHb measurement when determining whether HBOT should be considered.