Rate-Volume Ratio (Rvr) - Dräger Babylog 8000 plus Instructions For Use Manual

Description
Monitoring functions
Possible falsification of the results by the above-mentioned
conditions is indicated by a warning symbol on the screen. This
is displayed if r is less than 0.95, if the leakage in the displayed
curve is greater than 20 % or if there is strong spontaneous
breathing.
For the overdistension index, the ratio C
the volume increase from the last 20 % of the inspiration pres-
sure and is referred to the dynamic compliance [*]:
= (V(T ) – V(t80)) / (0.2 • P
C
20 I
The results remain displayed until the next evaluation cycle
has been completed. If, however, no new measured values are
available within one minute, the display is cleared.

Rate-Volume Ratio (RVR)

The ratio of the breathing rate to the tidal volume can help to
assess the chances of successfully weaning the patient from
the ventilator**. The Babylog 8000 plus calculates and displays
the RVR. In order to avoid fluctuations of the measured value
due to switching between spontaneous and mandatory
breathing cycles, the ratio between the rate and the volume is
not formed directly. Instead, the RVR is calculated with the
formula
2
RVR = f / VT = f / MV
which is equivalent to averaging the RVR over a period of
10 to 15 seconds.
* Identifying lung overdistention during mechanical ventilation by using
volume-pressure loops by Joel B. Fisher, Mark C. Mammel, Michael
C. Coleman, Dennis R. Bing, Stephen J. Boros Pediatric Pulmonol-
ogy 5:10-14 (1988)
** A prospective study of indexes predicting the outcome of trials of
weaning from mechanical ventilation; by Karl L. Yang,
Martin J. Tobin The New England Journal of Medicine,
Vol 324, 21, 1991
128
is calculated from
20
)
peak
V
V (Tin)
V (t80)
Paw
Paw (t80) Peak