One hour of simulated descent in a hyperbaric chamber improved immediate clinical state in patients with mild acute mountain sickness, but did not significantly improve patients in the longer term.

Clinical Bottom Line:
1. One hour of treatment by simulated descent was associated with significant clinical improvement.
2. There was no significant improvement in clinical state at twelve hours following treatment, although fewer hyperbaric patients received anti-emetics in the 12 hours following treatment.
Appraised by: Mike Bennett, Dept. of Diving and Hyperbaric Medicine, Prince of Wales Hospital, Sydney; Monday, 5 April 1999

Clinical Scenario: A patient with acute mountain sickness for treatment. We wondered if simulated descent using an inflatable hyperbaric chamber would improve symptoms.
Three-part Question: In the treatment of mild acute mountain sickness, does the administration of hyperbaric air to simulate descent, compared to bed rest, result in any improvement in symptoms or rate of recovery?
Search Terms: altitude sickness, hyperbaric air.

The Study:
Non-blinded concealed randomised controlled trial without intention-to-treat.
Mountaineers suffering from mild mountain sickness with headache and at least one of dizziness, nausea, insomnia, facial oedema or ataxia. Patients with symptoms of high altitude pulmonary oedema were excluded.
Control group (N = 33; 33 analysed): Rest and mild analgesia. Two groups of control, one not pressurised and resting in the chamber for one hour, the other compressed to sham hyperbaric treatment by application of about 20mbar for one hour.
Experimental group (N = 31; 31 analysed): As above, but treated for one hour at 193mbar in the chamber (equivalent to a descent of 2,250m).

The Evidence:

Time to Outcome
Control group
Pressure group
Relative risk reduction
Absolute risk reduction
Analgesia after treatment period
12 hours
95% CI:

-17% to 50%
-0.12 to 0.35
NNT=3 to INF NNH=8 to INF
Anti-emetics after treatment period
12 hours
95% CI:

3% to 100%
0.01 to 0.35
3 to 142

Non-Event Outcomes Time to outcome Control group Pressure group P-value
Clinical severity
Score 1 hour 1.4 2.7 <0.001

Clinical severity
score 12 hours 2.7 2.5 0.29

1. Control group treatment changed during study due to apparent clinical effect of placebo compression. Suggests no outcome blinding.
2. Beneficial short-term effect is probably due to improved oxygenation.
3. Efficacy of longer or more frequent treatments at pressure remains unknown.
4. Fewer anti-emetics required here in the active group when two control groups analysed together, not reported in paper.

Expiry date: April 2003
References: 1. Bartsch P, Merki B, Hofstetter D, Maggiorini M, Kayser B, Oelz O. Treatment of acute mountain sickness by simulated descent: a randomised controlled trial. British Medical Journal 1993; 306:1098-1101.