Dräger Evita 4 - Asb

165
Description
Ventilation Modes
ASB
Assisted Spontaneous Breathing
Pressure support for insufficient spontaneous breathing.
The function of the machine in assisting insufficient
spontaneous breathing is similar to that of the anaesthe-
tist who manually assists and monitors the patient's
spontaneous breathing by feeling the breathing bag.
The machine takes over part of the inhalation function,
with the patient maintaining control of spontaneous
breathing.
The CPAP system supplies the spontaneously breathing
patient with the breathing gas, even if the inspiration
effort is weak.
The pressure support of the ASB system is started:
– when the spontaneous inspiration flow reaches the
set value of the Flowtrigger, or at the latest
– when the spontaneous inspired volume exceeds
25 mL (12 mL in paediatric mode).
The machine then produces an increase in pressure up
to the preselected ASB pressure PASB, which is
adjustable to the breathing requirement of the patient.
The time for this pressure increase is adjustable from
64 milliseconds to 2 seconds.
With a rapid increase in pressure
Evita 4 supports the insufficient spontaneous breathing
of the patient with a high peak flow.
With a slow increase in pressure
Evita 4 begins gently with regular inspiratory flow. The
patient has to take over more breathing effort, and tone of
breathing muscles improves.
With the patient adjusted pressure increase and the
present ASB level, the patient's own breathing activity
defines the required inspiration flow, which can rise in
8 ms to 2 L/s.
ASB is terminated:
– when the inspiration flow returns to zero during
phase I, i.e. when the patient exhales or fights the
ventilator,
or
– when the inspiration flow in phase II falls below a
certain ratio of the maximum value previously supplied:
for adult ventilation: 25 % Insp.Flow
for paediatric ventilation: 25 % Insp.Flow
or
– at the latest after 4 seconds (1.5 seconds in
paediatric ventilation) if the two other criteria have not
come into operation.
If this 4-second criteria occurs three times in
succession, Evita 4 sounds an alarm and warns of a
possible leak in the ventilation system.
Phase
I II
Prescribed ideal
airway pressure
Paw
Insp.
Flow
t
t
P
ASB
CPAP
Start of inspiration
max. 4 s
End of inspiration
25 % Insp.Flow for adults
6 % Insp.Flow for paediatrics
25 % Insp.Flow for adults
25 % Insp.Flow for paediatrics