Weaver

Hyperbaric oxygen therapy reduced the incidence of cognitive sequelae following carbon monoxide poisoning.

Clinical Bottom Line: 1. HBOT significantly reduced the proportion of patients with cognitive sequelae at 6 weeks. 2. This effect may persist for 12 months, but the benefit was no longer statistically significant, perhaps due to data loss.

'C'itation/s: 1. Weaver LK, Hopkins RO, Chan KJ et al. Hyperbaric oxygen for acute carbon monoxide poisoning. New England Journal of Medicine, Vol347, No14 (pp. 1057 - 1066) 2. Weaver LK, Hopkins RO, Larson-Lohr V et al.Double-blind, controlled, prospective, randomized clinical trial (RCT) in patients with acute carbon monoxide (CO) poisoning: outcome of patients treated with normobaric oxygen or hyperbaric oxygen (HBO2) - an interim report. Undersea and Hyperbaric Medicine 1995 (Supl):14. 3. Weaver LK, Hopkins RO, Larson-Lohr V et al. (Same title). International Joint Meeting on Hyperbaric and Underwater Medicine Proceedings, Marroni A, Oriani G, Wattel F eds. 1996:333-334. 4. Hopkins RO, Weaver LK, Valentine KJ, Mower C, Churchill S, Carlquist J. Apolipoprotein E genotype and response of carbon monoxide poisoning to hyperbaric oxygen treatment. American journal of respiratory and critical care medicine. 2007 Nov 15;176(10):1001-6.

Three-part Clinical Question: For patients with acute carbon monoxide poisoning, does hyperbaric oxygen therapy, compared to normobaric oxygen therapy, reduce the incidence of long-term cognitive sequelae? Search Terms: Hyperbaric oxygenation, carbon monoxide poisoning

The Study: Double-blinded concealed randomised controlled trial with intention-to-treat. The Study Patients: Non-moribund patients with a diagnosis of acute, symptomatic carbon monoxide poisoning. Control group (N = 76; 76 analysed): Normobaric oxygen therapy: 1st session: 100% O2 at 1ATA for total time of 150 mins. 2nd and 3rd sessions: air at 1 ATA for total time 120 mins. Experimental group (N = 76; 76 analysed): Hyperbaric oxygen therapy: 1st session: 100% O2 at 2 then 3 ATA. 2nd and 3rd sessions: 100% O2 at 2 ATA. Session times as above.

The Evidence:

Outcome	Time to outcome	Normobaricgroup	Hyperbaricgroup	RRR	ARR	NNT
Cognitive sequelae	6 weeks	.461	.250	46%	.211	5
95% CI				14 to 78%	.063 to .359	3 to 16
Cognitive sequelae	6 months	.382	.211	45%	.171	6
95% CI				7 to 82%	.028 to .314	3 to 35
Cognitive sequelae	12 months	.329	.184	44%	.145	7
95% CI				2 to 86%	.008 to .282	4 to 124

Comments: 1.This a well conducted study of high methodological rigor. Most subjects were mildly poisoned. 2. Less than 80% follow-up at 6 months (77%). 3. Main benefits were reported for memory and attention. No measure of effect on life. 4. Data loss was dealt with by conservative assumptions as to the state of patients lost to follow-up. These are the figures used above. Analysis of the actual data by intention to treat suggests loss of statistical significance at 12 months (P=0.08). The suggested benefit from HBOT at 6 and 12 months is sensitive to best case/worst case analysis for missing data . For example, at 12 months best case yields a significant benefit of HBOT (NNT 4, 95%CI 3 - 8), while worst case suggests no significant difference between the arms (NNH 15, 5 - inf). Thus, we have less confidence in the preservation of effect at 6 and 12 months, although there is a trend to benefit. 5. Authors analysed a subgroup of 86 patients for any influence of the genetic marker of poor outcome, the apolipoprotein e4 allele, on cognitive function at six weeks. The e4 allele was not associated with 6-week cognitive sequelae, 27% (15/55) without and 32% (10/31) with the e4 allele (P = 0.3).

Appraised by: Dr Juliette Leverment and Mike Bennett, Hyperbaric Unit, Prince of Wales Hospital, Randwick, NSW 2026, Australia. Fax +61 02 9382 3882; 21 October 2002 Email: [julietteleverment@hotmail.com]

Kill or Update By: August 2022

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