Scheinkestel
Hyperbaric oxygen for patients carbon monoxide poisoning and was associated with a higher rate of delayed neurological sequelae.
Clinical Bottom Line: 1. There was no benefit evident for hyperbaric oxygen in the prevention of persistent neurologic abnormality. 2. There were significantly fewer patients with delayed neurologic abnormality in the normobaric group
Appraised by: Mike Bennett, Dept of Diving and Hyperbaric Medicine, Prince of Wales Hospital, Sydney; Monday, 1 March 1999
Clinical Scenario: A patient presented with acute carbon monoxide intoxication. Three-part Question: In patients with carbon monoxide poisoning, does the administration of hyperbaric oxygen, compared to normobaric oxygen, result in any improvement in the acute neurological state or the avoidance of late neurological deterioration? Search Terms: Hyperbaric oxygenation, carbon monoxide
The Study: Double-blinded concealed randomised controlled trial with intention-to-treat. Patients referred to a hyperbaric facility for the treatment of carbon monoxide poisoning- all grades of severity. Control group (N = 87; 87 analysed): Normobaric oxygen at 1ATA for 72 hour with three periods of sham hyperbaric oxygen. Those with persistent symptoms or signs received three further daily sham treatments and a further 72 hours on oxygen. Experimental group (N = 104; 104 analysed): Daily hyperbaric oxygen at 2.8ATA for 60 minutes (total chamber time 100 minutes) for three days with normobaric oxygen between treatments. Treatment repeated for another three days if symptoms or signs persisted.
The Evidence:
| Outcome | Time to Outcome | Normobaric group | HBO group | Relative risk increase | Absolute risk increase | NNH |
| Persistent neurologic sequelae | Discharge | 0.68 | 0.74 | 9% | 0.06 | 17 |
| 95% CI: | -10% to 28% | -0.07 to 0.19 | NNT14 to INF NNH5 to INF | |||
| Delayed neurologic sequelae | Unknown | 0 | 0.048 | INF | 0.05 | 21 |
| 95% CI: | 0.01 to 0.09 | 11 to 154 | ||||
| Complications of treatment | Discharge | 0.01 | 0.09 | 800% | 0.08 | 13 |
| 95% CI: | 0.02 to -0.14 | 7 to 47 |
Non-Event Outcomes Time to outcome Normobaric group HBO group P-value Ave number of neuropsych tests abnormal discharge 2.7 3.4 0.02
Comments: 1. Oxygen doses high in comparison to those generally administered. 2. Cluster randomisation may introduce some bias. 3. Average delay to treatment was over 7 hours. 4. Minimal improvement in mini-mental state assessment before and after treatment in either group is puzzling. 5. No functional outcome other than mortality. 6. Follow-up at one month only 46%.
Expiry date: August 2022
References: 1. Scheinkestel CD, Bailey M, Myles PS, Jones K, Cooper DJ, Millar IL, Tuxen DV. Hyperbaric or normobaric oxygen for acute carbon monoxide poisoning: a randomised controlled clinical trial. Medical Journal of Australia 1999; 170:203-210.
