21
gauge reading is less than 70 cm H
2
O.
c) Compliance factor (C
M
) of system, without patient connected, is:
C
M
=
Tidal Volume (V
t
)
Pressure Gauge Reading (P)
Note: V
t
= V
I
x T
I
The compliance factor of the MVP-10 with patient circuit is
approximately 0.12 ml/cm H
2
O. With a humidifier connected, it is
between 0.2 and 0.5 ml/cm H
2
O, depending upon the humidifier,
its water level and connecting hoses.
A compliance factor of 0.5 ml/cm H
2
O means that 0.5 ml of gas is
stored in the patient circuit and humidifier for each cm H
2
O of
pressure during the respiratory cycle, and does not go to the
patient. In the example in STEP 5, assume that the pressure
gauge reaches 10 cm H
2
O during the cycle. This would mean
that 10 x 0.5 or 5 ml is stored in the circuit. The apparent tidal
volume is 10 ml, but only a 5 ml tidal volume would be delivered
to the patient.
STEP 7 Compensate for the compliance of the system by increasing total flow.
In the previous example, 5 ml must be supplied for the compliance in
the system, as well as the prescribed 10 ml tidal volume for the
patient. Therefore, adjust flow rate to supply a 15 ml tidal volume:
Adjusted Flow = 15 ml x 120 = 1800 ml/min (1.8 liters/min)
The pressure gauge reading will increase a little, because of the
greater volume in the system, to say, 12 cm H
2
O. Compliance volume
would now be 12 x 0.5, or 6 ml, and a tidal volume of 9 ml would be
supplied to the patient.
To more closely obtain the prescribed tidal volume, a second
compensatory increase in flow is necessary. With flow increased to 2
liters/min, or about 33 ml/sec., the pressure gauge may indicate 13
cmH
2
O. The volume per cycle would now be 33 ml/sec. x 0.5 sec., or
16.5 ml. The compliance volume would be 13 x 0.5, or 6.5 ml, and the
prescribed tidal volume of 10 ml would be supplied to the patient.
STEP 8 Volume-limited or pressure-limited operation may be established as
follows:
a) For Volume-limited operation - Set the PIP control fully
counterclockwise.
