Hyperbaric (HBO) or normobaric oxygen (NBO) in the treatment of carbon monoxide poisoning

Date First Published:
July 26, 2000
Last Updated:
September 7, 2001
Report by:
Carolyn Meredith, Specialist Registrar (St Mary's hospital, London)
Search checked by:
Gregory Thomas, St Mary's hospital, London
Three-Part Question:
In [adult patients with carbon monoxide poisoning] does [hyperbaric oxygen when compared to normobaric oxygen] reduce [mortality and the incidence of persistent (PNS) or delayed neuropsychological sequelae (DNS)]?
Clinical Scenario:
A patient is brought in after attempting suicide by inhaling exhaust fumes from their car. He/she has a GCS of 3 and has required intubation but is otherwise stable. He/she has a carboxyhaemoglobin level of 40%. They have been receiving high flow oxygen, but you wonder if transfer for hyperbaric oxygen therapy is indicated.
Search Strategy:
Medline 1966-08/01 using the OVID interface.
Search Details:
({exp carbon monoxide poisoning OR carbon monoxide poisoning.mp} AND {exp hyperbaric oxygenation OR hyperbaric oxygen$.mp}) LIMIT to human AND english.
Outcome:
Altogether 299 papers were found of which 294 were irrelevant or of insufficient quality for inclusion. The remaining 5 papers are shown in the table.
Relevant Paper(s):
Study Title Patient Group Study type (level of evidence) Outcomes Key results Study Weaknesses
Acute carbon monoxide poisoning. Risk of late sequelae and treatment by hyperbaric oxygen. Mathieu D, Nolf M, Durocher A, et al. 1985, France 575 Non-comatose adults with CO poisoning
Interim analysis <12 hours
HBO 90 min 2.5 ATA v NBO (100%) 12 hrs
 prospective randomized controlled trial Neurological signs and symptoms Significantly fewer persistent neurological manifestations in HBO group at 3 months, no difference at 6-12 months Not blinded, no sham treatments
Completed study not available
Trial of normobaric and hyperbaric oxygen for acute carbon monoxide intoxication. Raphael JC, Elkharrat D, Jars-Guincestre MC, et al. 1989, France 629 adults with CO poisoning
1. Patients with no LOC-6 hrs NBO (100%) V 2 hrs HBO
2. Patients with initial or persisting LOC-HBO x2 hrs v NBO (100%) x 4 hours		 prospective randomized controlled trial self assessment questionnaire or postal/telephone questionnaire No difference in % recovery between 2 groups at 1 month 54% v 52% (p=0.75). 2 deaths in each group Not blinded, no sham treatments
Outcome measures not standardised
% recovery at 1 month - Symptoms, Physical signs No difference in % recovery between 2 groups at 1 month 66% v 68% (p=0.75).
Non-comatose patients with acute carbon monoxide posioning: hyperbaric or normobaric oxygenation? Ducasse JL, Celsis P, Marc-Vergnes JP. 1995, France 26 non-comatose adults with CO poisoning
HBO 2 hours (+NBO 100% 4 hrs, 50% 6 hrs) versus
NBO (100% 6 hrs, 50% 6 hrs)
 Prospective randomised controlled trial Symptoms and physical signs at 2 hours+12 hours Significantly slower recovery in NBO group. All asymptomatic at discharge Small numbers
Not blinded, no sham treatments
EEG EEG- More abnormalities at 3 weeks in NBO group
Delayed neuropsychologic sequelae after carbon monoxide poisoning: prevention by treatment with hyperbaric oxygen. Thom SR, Taber RL, Mendiguren II, et al. 1995, USA
63 adults with CO poisoning
NBO (100%) v HBO 2.8 ATA 30 min + 2 ATA 90 min
 Prospective randomised controlled trial % with delayed neurological sequelae (signs and symptoms and psychometric evaluation) post treatment at 1 week and 1 month DNS seen in 8 (23%) NBO group. None in HBO group. All fully recovered 41 days. Not blinded, no sham treatments
Small numbers
Psychometric evaluation compared with only 8 healthy volunteers
Hyperbaric or normobaric oxygen for acute carbon monoxide poisoning: a randomised controlled clinical trial. Scheinkestel CD, Bailey M, Myles PS, et al. 1999, Australia 191 adult patients with CO poisoning
(comatose and non comatose)
NBO (100%) 3 days + sham treatments v HBO 1 hour for 3 days 2.8 ATA
 Prospective randomised controlled trial. Double-blinded outcome assessment. Neuropsychological performance on treatment completion + 1 month PNS 62% at follow up - no difference between 2 groups. DNS (5) only seen in HBO group (p=0.03). Neuropsychological testing - significantly lower number of abnormal tests in NBO group at completion of treatment Cluster randomisation
Only 46% attended 1 month follow up
HBO treatment delay (mean 7.1 hrs)
Mortality rates Mortality- no significant difference between 2 groups
Author Commentary:
Studies vary in their inclusion criteria (presence of symptoms, COHb level, all emergency referrals) and in their treatment regimes and time to treatment. Whilst there are studies (non-randomised and randomised) suggesting benefit of HBO over NBO therapy in carbon monoxide poisoning, only one study (Scheinkestel et al) was double-blinded, utilitzing sham therapies. This study showed no benefit of HBO therapy over NBO treatment. The conclusions of this BET are similar to that of a Cochrane Review (6).
Bottom Line:
There is no evidence of an advantage in terms of mortality and neurological sequelae of hyperbaric oxygen therapy over 3 days of high flow normorbaric oxygen for patients with all grades of CO poisoning.
References:
  1. Mathieu D, Nolf M, Durocher A, et al.. Acute carbon monoxide poisoning. Risk of late sequelae and treatment by hyperbaric oxygen.
  2. Raphael JC, Elkharrat D, Jars-Guincestre MC, et al.. Trial of normobaric and hyperbaric oxygen for acute carbon monoxide intoxication.
  3. Ducasse JL, Celsis P, Marc-Vergnes JP.. Non-comatose patients with acute carbon monoxide posioning: hyperbaric or normobaric oxygenation?
  4. Thom SR, Taber RL, Mendiguren II, et al.. Delayed neuropsychologic sequelae after carbon monoxide poisoning: prevention by treatment with hyperbaric oxygen.
  5. Scheinkestel CD, Bailey M, Myles PS, et al.. Hyperbaric or normobaric oxygen for acute carbon monoxide poisoning: a randomised controlled clinical trial.
  6. Juurlink DN, Stanbrook MB, McGuigan MA.. Hyperbaric oxygen for carbon monoxide poisoning (Cochrane Review).