Dräger Babylog 8000 plus Operating Instructions Manual page 141

Theory of Operation
Ventilation Monitoring
An on-screen warning symbol is used to indicate a
possible condition of calculated values being affected in
such fashion. This means that r is less than 0.95, the leak
rate in the breath just evaluated is more than 20 %, or
that considerable spontaneous breathing is detected.
For calculation of the overdistension coefficient C , the
20
volume increase attributable to the last 20 % of the inspi-
ratory pressure is determined and related to the dynamic
compliance [1]:
)) / (0.2 . P
C = (V(T ) - V( )
20 in t80 peak
An overdistended lung becomes stiffer towards the end
of inspiration, resulting in reduced volume increase
during the final 20 % of inspiratory pressure. As a conse-
quence, C20/C will be less than 1, indicating overdisten-
tion. However, this condition can be detected reliably
only if there is no pressure plateau, or only a short
plateau. The sooner the plateau sets in during inspiration,
the less significant the value of C20/C will be.
The results are displayed until a new evaluation is
complete. However, if no new values are obtained within
a minute, the display is cancelled.
[1]
Identifying lung overdistension during mechanical ventilation by using
volume-pressure loops
Joel B.Fisher, Mark C. Mammel, Michael C. Coleman, Dennis R. Bing,
Stephen J. Boros
Pediatric Pulmonology 5:10-14 (1988)
141