ResMed Elisee 150 Clinical Manual page 61

Reaching the minimum tidal volume (V
V
Ti
(inst)
Ti(inst)
Vadm
Figure 4.28: Minimum tidal volume (V
At any given moment:
Ti Max - Ti(inst) = Trem
where
Trem = time remaining in the cycle
The following calculation is constantly applied to determine whether maintaining the
instantaneous flow ( inst) until the end of the cycle will allow a volume higher than the target
minimum tidal volume to be reached.
inst x Trem > minimum V
V
As soon as this expression ceases to be true, the calculated instantaneous flow must be
maintained until the end of the cycle to ensure the target minimum V
Expiratory phase
When the cycle is entirely spontaneous (the device does not switch to volumetric mode), cycling
to expiration occurs in the same way as in PS.SV (PS) mode (see "Figure 4.25: Expiratory phases
in PS.SV (PS) mode." on page 57):
•
When the expiratory trigger setting is reached; the setting may be:
•
based on the peak flow drop (Scenario No. 1);
•
an automatic setting based on the intersection of the flow curve with the 3 second line
(Scenario No. 2).
•
If the set pressure of 2cmH
have initiated active exhalation (Scenario No. 3).
•
When the maximum inspiratory time set by the user is reached (Scenario No. 4), if none of
the above conditions are met. This scenario can occur if there are leaks in the circuit, or if the
flow doesn't decrease sufficiently to reach the expiratory trigger setting.
When the ventilator switches to volumetric mode (constant ventilatory flow) in order to reach the
target tidal volume within the time allowed (Ti Max), cycling occurs:
•
at the end of the maximum inspiratory time (Ti Max).
•
or if the pressure in the circuit reaches the Pmax safety threshold and the inspiratory flow is
maintained at a constant level, causing a peak in pressure.
Generally speaking, this function provides a high level of safety, particularly for patients receiving
invasive ventilation. The purpose of this mode is to address the main disadvantage of PS.SV (PS)
NOT013189-6
V
inst
T
rem
Ti max
= Time since the start of inspiration
= Tidal volume already administrated (Air flow integrated during Ti(inst))
) calculation in PS.VT mode.
t
V
– delivered V
T
O is exceeded during the decreasing flow stage, the patient may
2
)
T
t
T
T
is reached.
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