HBO Versus NBO for Carbon Monoxide Poisoning

5 min read · 21 August 2026

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“Randomized Prospective Study Comparing the Effect of HBO Versus 12 Hours NBO in Non Comatose CO Poisoned Patients: Results of the Interim Analysis” is a 1996 meeting abstract by Mathieu and colleagues. It addresses oxygen treatment for carbon monoxide poisoning, a subject relevant to hyperbaric medicine and to divers because both involve oxygen under pressure and the risks of impaired oxygen delivery to tissues.

What is the treatment question?

The title sets out a comparison between hyperbaric oxygen (HBO) and twelve hours of normobaric oxygen (NBO) in patients with carbon monoxide poisoning who were not comatose. HBO means breathing oxygen in a chamber at increased ambient pressure; NBO means breathing oxygen at ordinary atmospheric pressure. The clinical question is how these different oxygen-delivery conditions are examined in a prospective, randomized comparison.

Carbon monoxide interferes with the blood’s ability to transport oxygen by binding to haemoglobin. The resulting tissue oxygen deprivation can affect the brain, heart and other organs, while symptoms and severity vary. A person need not be comatose for poisoning to be medically serious, which makes assessment and treatment decisions important even when consciousness is preserved.

Why compare oxygen at different pressures?

Breathing oxygen raises the amount of oxygen available to the body, while increased ambient pressure also increases the amount that can dissolve in blood plasma. Hyperbaric treatment therefore changes both the oxygen environment and the pressure under which treatment takes place. Comparing it with oxygen delivered at normal pressure addresses whether the treatment setting matters for the patient group under study.

The title identifies a randomized prospective design. In general, random assignment is used to reduce the influence of pre-existing differences between treatment groups, while prospective study design follows participants after the treatment approach is assigned. An interim analysis is an examination conducted before a study is complete; the phrase signals a stage of analysis, not a final verdict about clinical practice.

HBO: oxygen breathing in a pressurised chamber.
NBO: oxygen breathing at ordinary ambient pressure.
Carbon monoxide poisoning: impaired oxygen transport and delivery to tissues.
Non-comatose patients: the patient group specified by the publication’s title.

What makes carbon monoxide relevant to diving medicine?

Diving medicine routinely considers how pressure, breathing gases and oxygen availability interact. Carbon monoxide exposure is a distinct poisoning problem rather than a form of decompression illness, but the need to recognise compromised oxygen delivery links it to broader concerns in hyperbaric care. A chamber may be used in different clinical contexts, so treatment rationale and patient assessment must not be conflated.

For divers, contaminated breathing gas can be a potential source of carbon monoxide exposure. Headache, confusion, weakness or other nonspecific symptoms after a dive can have several possible causes, and suspected poisoning calls for urgent medical assessment rather than self-diagnosis. A diving-medicine physician should be consulted when evaluating dive-related illness or decisions about return to diving.

How does this subject fit into hyperbaric research?

Hyperbaric medicine studies when increased pressure and oxygen may have a role in treating illness, as well as the practical and physiological considerations that accompany chamber treatment. Carbon monoxide poisoning has long been one of the clinical questions in this field: the central issue is how best to restore oxygen availability and address the potential consequences of exposure. Comparing HBO with NBO is one way to frame that question.

Research designs and treatment protocols matter because oxygen is both essential and biologically active, while pressurised treatment involves specific clinical and operational considerations. The title places this work within the evidence-building process, but a meeting abstract should not be treated as a universal treatment rule. Individual care depends on clinical assessment and the applicable medical setting.

Frequently asked questions

What do HBO and NBO mean?

HBO is oxygen breathing under increased ambient pressure in a chamber. NBO is oxygen breathing at ordinary atmospheric pressure.

Why does carbon monoxide poisoning affect oxygen delivery?

Carbon monoxide binds to haemoglobin and interferes with its oxygen-carrying role, potentially depriving tissues of oxygen.

Is carbon monoxide poisoning the same as decompression illness?

No. They are different conditions with different mechanisms, although both can arise in contexts relevant to diving medicine and may require specialised medical assessment.

Citation details

Title: Randomized Prospective Study Comparing the Effect of HBO Versus 12 Hours NBO in Non Comatose CO Poisoned Patients: Results of the Interim Analysis
Authors: Mathieu, D; Wattel, F; Mathieu-Nolf, M; Durak, C; Tempe, JP; Bouachour, G; Sainty, JM
Year: 1996
Published in: Undersea & Hyperbaric Medicine 1996
Record type: Meeting abstract
Repository record: Rubicon Research Repository, handle 123456789/447

This page is an original summary written by the Rubicon editors from the publication’s bibliographic record. It does not reproduce the paper, its abstract or its data; consult the publication itself for its methods and findings.