Dräger Babylog 8000 plus Instructions For Use Manual page 167

This diagram shows the relationship between
sensitivity and Vtrig. At the highest sensitivity, Vtrig
= 0. In this case the inspiratory flow need only
reach the minimum value of 0.2 L/min to trigger a
breath. There is also the possibility, however, that
artifacts will cause auto-triggering. If the device
auto-triggers, it may be necessary to reduce the
sensitivity.
The lower the sensitivity, the longer the delay
between spontaneous inspiration and the
mechanical breath. It may not become so long that
the mechanical inspiration hinders spontaneous
expiration. In this case, the patient would be
fighting against the ventilator. Choosing the ideal
sensitivity is always a compromise between the
shortest possible trigger delay and reliable
protection against auto-triggering.
Instructions for use Babylog 8000 plus SW 5.n
Lung-mechanics parameters
Using the waveforms for pressure, flow, and
volume, the device calculates the following
parameters for a ventilation cycle comprising
inspiration and expiration:
Parameter Explanation
C Dynamic compliance of the respira-
tory system using the linear-regres-
sion method
R Resistance of the airways and
endotracheal tube using the linear-
regression method
r Correlation coefficient
Tc Time constant of the respiratory
system (Tc = R x C)
C /C Overinflation index according to
20
1) 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
Pulmonology, 5:10-14 (1988)
The device first saves all measured values Paw(t),
Flow(t), and V(t) for a ventilation cycle of up to
5 seconds in length. 120 measured values are
taken per second. The data are evaluated and the
results are displayed. Then another ventilation
cycle is saved, and so forth. The displayed results
thus are not for the current mechanical breath, but
are generally several seconds old.
The calculation uses the following equation:
Paw = R x Flow + V/C
This equation applies to a single-compartment
model of the respiratory system at any point during
a mechanical breath. Resistance and compliance
are assumed to be constant. For the measured
values pressure, flow, and volume, the regression
method determines the values for R and C that
best fit with the measured data. One measure of
conformity is the correlation coefficient r, a number
between 0 and 1. The closer the correlation
coefficient r is to 1, the better the conformity.
Principles of operation
1)
167