Air Break During Preoxygenation and Risk of Altitude Decompression Sickness

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA530698&Location=U2&doc=GetTRDoc.pdf


Air Break During Preoxygenation and Risk of Altitude Decompression Sickness


P ILMANIS AA, W EBB JT, B ALLDIN UI, C ONKIN J, F ISCHER JR. Air break
during preoxygenation and risk of altitude decompression sickness.
Aviat Space Environ Med 2010; 81: 944 – 50 .
Introduction: To reduce the risk of decompression sickness (DCS),
current USAF U-2 operations require a 1-h preoxygenation (PreOx). An
interruption of oxygen breathing with air breathing currently requires
signifi cant extension of the PreOx time. The purpose of this study was to
evaluate the relationship between air breaks during PreOx and subsequent
DCS and venous gas emboli (VGE) incidence, and to determine
safe air break limits for operational activities. Methods: Volunteers
performed 30 min of PreOx, followed by either a 10-min, 20-min, or
60-min air break, then completed another 30 min of PreOx, and began
a 4-h altitude chamber exposure to 9144 m (30,000 ft). Subjects were
monitored for VGE using echocardiography. Altitude exposure was
terminated if DCS symptoms developed. Control data (uninterrupted
60-min PreOx) to compare against air break data were taken from the
AFRL DCS database. Results: At 1 h of altitude exposure, DCS rates were
signifi cantly higher in all three break in prebreathe (BiP) profiles compared
to control (40%, 45%, and 47% vs. 24%). At 2 h, the 20-min and
60-min BiP DCS rates remained higher than control (70% and 69% vs.
52%), but no differences were found at 4 h. No differences in VGE rates
were found between the BiP profiles and control. Discussion: Increased
DCS risk in the BiP profi les is likely due to tissue renitrogenation during
air breaks not totally compensated for by the remaining PreOx following
the air breaks. Air breaks of 10 min or more occurring in the middle of
1 h of PreOx may signifi cantly increase DCS risk during the first 2 h
of exposure to 9144 m when compared to uninterrupted PreOx
exposures.