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 |
NNT=14
to INF NNH=5 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: September 2004
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.
