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ADF Health September 2002 - Volume 3 Number 2

Letters to the Editor

The Western Front pilgrimage for World War I veterans, 1993

• Air Commodore Roger A Capps, AM, RFD, FANZCA, DipD&HM
  Department of Anaesthesia, Royal Adelaide Hospital, Adelaide, SA 5000.
  Correspondence: Air Commodore Roger A Capps, Department of Anaesthesia, Royal Adelaide Hospital, North Terrace, Adelaide, SA 5000. rcapps@mail.rah.sa.gov.au

IN REPLY: Lieutenant Colonel Allen, referring to sleep apnoea, recommends that "the subject undergo a case-specific assessment". Among the veterans we were assessing there were none whose histories suggested the likelihood of sleep apnoea, hence there was no indication for undertaking sleep studies before final selection.

In our article, we did mention sleep apnoea, as this was considered a possibility in Veteran 5 during the flight. His temporary desaturation was readily reversed with his normal bronchoactive medication. There were no further desaturation events, making the diagnosis of sleep apnoea less than convincing. No other veterans were flagged as potential sufferers of sleep apnoea, and all were monitored at regular intervals visually, and by oximetry at least once during sleep. Cheyne-Stokes breathing was not mentioned in our article, as there was none among the veterans during assessment or while travelling.

I agree that a high altitude simulation test is easier and cheaper. Even though it would be absurd to suggest that all patients with cardiac or respiratory disease need to be tested in an altitude chamber, I would challenge the assertion that use of an altitude chamber is problematic. The chamber accurately and with ease provides the stepped rise in cabin altitude that could be expected on the flight, without adding nitrogen, a non-physiologically representative step suggested in Allen's recipe to achieve hypoxic conditions. The chamber allowed the easy addition and assessment of the effects of adding nasal oxygen prongs with variable oxygen flow rates, in the way we planned for the trip. The problem with a high altitude simulation test as described is that there is a single step to a less than accurate cabin altitude. The addition of nasal prongs to the high altitude simulation test mask as described would be impractical, if not impossible, and less accurate.

I challenge the assertion that the chamber run is potentially litigious. The run took the veterans to an easily controllable environment no more dangerous or challenging than they would experience on the flight. Indeed, it was safer, in that we had the ability to provide easily controllable simulated 1000ft or 2000ft steps to 8000ft. Each step was for as long as we wanted and was accompanied by full objective and subjective assessments. We did not go straight to "assigned altitude", as is the situation with the high altitude simulation test. The run could be aborted at any stage with ease.

Perhaps if Allen were to visit an altitude chamber, he would feel more comfortable with its safety.

In summary, I believe we provided an unusual but an accurate and safe environment in which we could assess the effects of altitude on a large group of aged veterans and predict their inflight oxygen requirements.