Instructions for use Babylog 8000 plus SW 5.n 157
Principles of operation
When the pressure reaches Pinsp, a pressure
plateau is created. If Pinsp is not reached, the
pressure curve has a sharp peak.
The pressure pattern determines what the tidal
volume VT depends on. The following two cases
show the relationship:
Case 1, long plateau:
If the plateau is so long that the inspiratory flow
has fallen to zero by the end of T
I, lung pressure
has reached airway pressure. The ventilation
pressure (the difference between Pinsp and
PEEP) then controls the tidal volume:
VT = (Pinsp – PEEP) x Crs
Crs: compliance of the respiratory system
Case 2, no plateau:
Without an inspiratory plateau Pinsp has no
influence. Part of the flow fills the breathing
circuit with each mechanical breath and does not
reach the lungs. Part of the ventilation solely
occurs in the breathing circuit. The tidal volume
can be approximated as follows:
VT = T
I x x (Crs / (Crs + Cs))
Cs: compliance of the breathing circuit
Especially in very small patients, the effect of the
breathing circuit can be detrimental because Cs
and Crs are of equal magnitude.
Example:
If Crs = Cs = 0.5 mL/mbar (0.5 mL/cmH
2O) only
half of the set flow reaches the lungs.
This effect of ventilating the breathing circuit
occurs with any ventilator. The flow sensor in
Babylog 8000 is located at the Y-piece in order to
measure the tidal volume that is actually inhaled
and exhaled.
insp
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