Dräger Evita 4 - Bipap

Description
Ventilation Modes
166
BIPAP
Biphasic Positive Airway Pressure
The BIPAP ventilation mode is a pressure/time-cycled
ventilation mode in which the patient can always breathe
spontaneously. BIPAP is therefore often described as a
time-cycled alternation between two CPAP levels.*
The time-cycled change of pressure gives controlled
ventilation, which corresponds to pressure-controlled
ventilation PCV. However, the constant option of spon-
taneous breathing allows the transition from controlled
breathing to independent spontaneous breathing to take
place smoothly via the weaning phase, without requiring
any change the ventilation mode. To adapt easily to the
patient's spontaneous breathing pattern, the change-over
from expiratory pressure level to inspiratory pressure
level, and also the change-over from inspiratory pressure
level to expiratory pressure level, are synchronised with
the patient's spontaneous breathing.
The frequency of the change-over is kept constant, even
when synchronisation occurs via a "trigger window" with
fixed time constant.
The "trigger window" is 5 seconds long in adult mode
and 1.5 seconds long in paediatric mode. For expiration
times shorter than 5 seconds or 1.5 seconds, the
"trigger window" covers the entire expiration time.
At Pinsp level, the "trigger window" is 1/4 · Tinsp seconds
long.
As recent clinical research** has shown, this smooth
adaptation to the patient's spontaneous breathing
requires less sedation, so that the patient returns to
spontaneous breathing more rapidly.
As in all pressure-controlled ventilation modes, the
patient is not prescribed a fixed tidal volume (VT).
The tidal volume results principally from the pressure
difference between the settings for PEEP and Pinsp.
Changes in lung compliance and airways, as well as
active breathing by the patient can lead to changes in
tidal volume. This is a desired effect in this ventilation
mode.
With the knowledge that the tidal volume, and therefore
the minute volume, are not constant, the alarm limits for
minute volume must be adjusted with care.
The display of the expiratory measured tidal volume VTe
must be used to set the required difference between the
two pressure levels. Any increase in differential will cause
an increased BIPAP ventilation stroke.
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* Bibliography (3), (4), (7), (11), (12), page 182
** Bibliography (8), page 182