Mathieu 1996.

Methods	Prospective, randomised, unblinded trial.
Participants	575 non‐comatose nonpregnant patients with no evidence of mixed poisoning, recruited over 3 years. COHb > 10%.
Interventions	HBO at 2.5 ATA for 90 minutes (plus 15 minutes each for compression and decompression) vs. 12 hours of NBO.
Outcomes	Neuropsychologic testing at 1, 3, 6, and 12 months. 'Persistent neurological manifestations' were present in 23% of HBO arm and 26% of NBO arm at 1 month, but detailed data were not presented.
Notes	Data from abstract of 1996 interim analysis only. This trial is not registered and no later data were available for analysis at the time of the 2005 or 2011 review. Author contacted in 2004 and 2010 but no further information provided.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	Quote: "After randomisation patients are treated either by a HBO session (2.5 ATA, 90 min) or by 12 hours normobaric pure oxygen."
Allocation concealment?	Unclear risk	Not mentioned.
Blinding? All outcomes	High risk	Not mentioned. Without sham therapy blinding would not be possible.
Incomplete outcome data addressed? All outcomes	High risk	Quote: "At 1 month, follow‐up shows fewer (although not statistically significant) persistent neurologic manifestations in the HBO group than in the NBO (23% vs 26%). At 3 months, a large significant difference exists (HBO: 9.5% vs NBO: 15%; p=0.016). The difference becomes less important at 6 months (6.4% vs 9.5%; p=0.09) and disappears at 1 year (4.3% vs 5%)." Comment: No information on drop‐outs provided.
Free of selective reporting?	Unclear risk	Quote: "Patients were all discharged from the hospital with a normal neurologic examination. At 1 month, follow‐up shows fewer (although not statistically significant) persistent neurologic manifestations in the HBO group than in the NBO (23% vs 26%). At 3 months, a large significant difference exists (HBO: 9.5% vs NBO: 15% ; p=0.016). The difference becomes less important at 6 months (6.4% vs 9.5% ; p=0.09) v and disappears at 1 year (4.3% vs 5%)." Quote: "The study is continued to allow proper subgroup analysis." Comment: Abstract published in 1996, the final report or a later interim analysis has not been presented in any forum.
Free of other bias?	Unclear risk	Power/sample size/interim analysis/publication: Quote: "An interim analysis was planned at the end of the third year". "The study is continued to allow proper subgroup analysis". Comment: No sample size calculation. No response to request for further information in 2004 or 2010.