Description; Principles Of Operation - BIO-MED DEVICES IC-2A Instruction Manual

II. DESCRIPTION
A. PRINCIPLES OF OPERATION
1. IPPV
With the CYCLE/CPAP-MANUAL selector set in cycle and NORMAL/SIMV
selector set in normal, the IC-2A acts as a controller or assist/controller. A
pilot valve operated by the timing signal from the fluid logic opens for a
preset length of time (Insp. Time) allowing gas to flow at some rate
established by the flow rate control. During this time the exhalation valve is
pressurized, closing the exhalation port and thus insuring that all gas is
directed to the patient. The gas supply is a high pressure source and since
the pressure reached in the patient is relatively low, the flow rate remains
constant, independent of changes in patient pressure. The ventilator is a
constant flow generator.
a.
b.
2. Synchronized Intermittent Mandatory Ventilation (SIMV)
The IC-2A provides a unique triggered demand-flow system for the addition
of a constant flow source. It obviates the need of check valve, flowmeter,
Volume Limited
The pressure developed in the system depends on the total
compliance and the volume of gas delivered. If the adjustable
pressure limit is set higher than the pressure that is reached, then no
gas is dumped to atmosphere and the ventilator is volume limited. In
this mode the tidal volume (V
flow rate.
In this mode the pressure limit is normally set 5-10 cmH
pressure attained. It then acts as an upper level failsafe. If patient
resistance or compliance cause a significant increase in pressure, the
pressure will be limited at the preset level. When this occurs the
ventilator is no longer volume limited since some gas is dumped to
atmosphere and therefore the tidal volume is unknown.
Pressure Limited
Whenever the pressure reached within the patient circuit is equal to
the maximum pressure limit established using the maximum pressure
control on the rear panel, the excess gas is dumped to atmosphere
and the unit is operating in a pressure-limited mode. The ventilator
may be used continuously in the pressure limited mode by setting the
maximum pressure and adjusting the inspiratory time and flow rate to
give a large enough volume of gas per breath to insure that the preset
pressure level is reached on each cycle. When the pressure limit is
reached, it is held until the end of inspiration thus producing a
"plateau" type pressure waveform.
The lowest rate attainable in the IPPV mode is established by the
backup timer at 6 breaths/min.
) is the product of inspiratory time and
t
V = T X V
t l l
O above the
2
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