Measurement Of Flow And Volume; Reference Condition; Leakage Rate - Dräger Babylog 8000 plus Instructions For Use Manual

Measurement of flow and volume

The flow is measured with a hot-wire anemometer in the
Y-piece or with a sensor fitted between the Y-piece and the
tube. The direction of flow is detected by using two hot wires,
one of which is shielded by a baffle on one side.
The lowest flow rate which can be detected reliably is
0.2 L/min. Flow rates below this are suppressed and displayed
as zero.
There are two different types of flow sensors available:
– the Y-sensor, integrated into the Y-piece and
– the ISO sensor, inserted between the Y-piece and the tube
connector.
Both types use the same sensor insert, but their characteristics
are nevertheless not identical. The type of flow sensor being
used is selected in the menu in order to optimise the measure-
ment function.

Reference condition

Primarily, hot-wire anemometers measure quantities of gas,
rather than volumes or flow rates. As defined in the state
equation for gases, the volume of a specific amount of gas
depends on the ambient conditions, namely atmospheric
pressure, temperature and relative humidity.
The Babylog 8000 plus displays the measured volume and
flow values for one of two different reference conditions:
– NTPD (temperature 20 °C, atmospheric pressure
1013 mbar, dry air) or
– BTPS (body temperature 37 °C, actual atmospheric
pressure, air saturated with moisture).
The desired reference condition is selected in the menu.

Leakage rate

If the tube is not a tight fit, some air will often escape between
the wall of the trachea and the tube.
Since the flow sensor of the Babylog 8000 plus is located in the
Y-piece, i.e. upstream of the leak, breathing gas is lost after
measurement during inspiration and before measurement
during expiration. The tidal volume measured on the inspiration
side is thus larger than the actual tidal volume, while that
measured on the expiration side is smaller. Averaged over
time, the difference between the inspiratory and expiratory flow
is equal to the leakage flow, since the amount of gas which
does not flow back through the sensor during expiration must
have escaped through the leak.
The Babylog 8000 plus determines the leakage flow from the
difference between the inspiratory minute volume MVi and the
expiratory minute volume MVe (which is displayed as MV).
Normalised for MVi, the leakage rate in percent displayed on
the screen is:
Leakage rate = 100 % • (MVi – MVe) / MVi
Description
Monitoring functions
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