Raphael

The administration of hyperbaric oxygen did not improve outcome in carbon monoxide poisoning without a history of loss of consciousness.

Clinical Bottom Line: 1. No evidence for benefit of hyperbaric oxygen in the treatment of carbon monoxide poisoning without loss of consciousness. 2. No evidence of benefit of two HBO sessions over a single session for patients with a history of loss of consciousness.

Appraised by:Mike Bennett, Dept of Diving and Hyperbaric Medicine, Prince of Wales Hospital Sydney, Saturday, 20 February 1999

Clinical Scenario:A patient presented with carbon monoxide poisoning for treatment. Three-part Question:In patients with mild and moderate carbon monoxide poisoning, does the administration of hyperbaric oxygen, compared to normobaric oxygen, result in any reduction in the rate of neurological impairment one month later? Search Terms:hyperbaric oxygenation, carbon monoxide

The Study: Non-blinded concealed randomised controlled trial with intention-to-treat. Adult patients exposed to carbon monoxide and presenting for treatment within 12 hours of exposure. Minimum carboxyhaemoglobin levels of 10% in smokers and 5% in non-smokers. Control groups1.(N = 170; 148 analysed): Patients with no history of unconsciousness. Normobaric 100% oxygen for six hours. 2.(N = 145; 127 analysed): Patients with a history of loss of consciousness. Oxygen at 2ATA for two hours then 1ATA for 4 hours. Experimental groups 1.(N = 173; 159 analysed): Patients with no history of unconsciousness. Oxygen at 2ATA for two hours then 1ATA for 4 hours. 2.(N = 141; 125 analysed) Patients with a history of loss of consciousness. Oxygen at 2ATA for two hours, then 1ATA for 4 hours, then 2ATA for a further two hours at 12 hours after the first HBO.

The Evidence:1.

Outcome	Time to Outcome	Control groups	Hyperbaric groups	Relative risk reduction	Absolute risk reduction	NNT
Recovered	1 month	0.662	0.679	-3%	-0.017	-59
95% CI:				-18% to 13%	-0.122 to 0.088	NNT 11 to INF NNH = 8 to INF
Persistent symptom	1 month	0.338	0.321	5%	0.017	59
95% CI:				-26% to 36%	-0.088 to 0.122	NNT 8 to INF NNH = 11 to INF

2.

Outcome	Time to Outcome	One HBO session	Two HBO sessions	Relative risk reduction	Absolute risk reduction	NNT
Recovery	1 month	0.535	0.52	3%	0.015	67
95% CI:				-20% to 26%	-0.108 to 0.138	NNT 7 to INF NNH = 9 to INF
Severe sequelae or death	1 month	0.039	0.048	-23%	-0.009	-111
95% CI:				-100% to 100%	-0.059 to 0.041	NNT 24 to INF NNH = 17 to INF

Comments: 1. Many very mildly poisoned patients were included which may bias towards the null. 2. Recovery was defined as the absence of any symptoms or signs on questionnaire and examination. 3. Best and worst case analysis of missing data does not alter conclusions. 4. The indication for HBO in those with a history of loss of consciousness has not been tested in this study.

Expiry date: August 2022

References: 1. Raphael J-C, ElkharratD, Chastang C, Chasles V, Vercken J-B, Gajdos P. Trial of normobaric and hyperbaric oxygen for acute carbon monoxide intoxication. Lancet 1989; 8658:414-419.

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