th
4
Lecture
Mechanical Ventilator
Part Two
Ventilator Block Diagram (1-2)
The main components of the ventilator
1) Two gas supplies:
The first one is to provide oxygen, the other is to
provide compressed air (a compressor may be ordered
as an alternate air source).
2) Pneumatic system:
System That mixes the gases, generates flow
waveforms, delivers volumes, and measure pressures.
3) Patient service systems:
System that routes the mixed gases to and from the
patient.
Ventilator Block Diagram (2-2)
4) keyboard and display panel
Is used to specify the operation mode of
pneumatic system, monitor patient and
ventilator performance, and notify the operator
with alarms when specified problems occur.
5) Microprocessor electronics:
control and monitor the pneumatic system, the
keyboard display panel, and the utility panel.
Ventilator Block Diagram
Ventilator Components
Power Requirements
• In general, the ventilator’s electrical and electronic
systems operate with DC power. However, the
optional compressor, the exhalation filter, and the
humidifier outlet are power by wall AC current.
• Internal batteries provide reserve power to memory
in the microprocessor electronics.
Microprocessor Electronics
Microprocessor Electronics
• The microprocessor receives information from
keyboard, utility panel, DC power supply, and
memory as well as from pressure switches and
temperature/flow sensors in the pneumatic system.
• The microprocessor monitors the information from
these sources and performs necessary calculations
based on programs stored in memory. As a result of
these calculations, status information and control
signals are sent to the pneumatic system and to the
displays.
Ventilator Components
Gas Supply System
• Both air and oxygen enter the ventilator through
filters that remove particulate matter (larger than
0.3 microns) and condensed moisture in aerosol
form. (Bulk water must be removed from wall air
sources with a separate water trap).
• The optional compressor enables the ventilator
to operate independently of compressed wall air.
Ventilator Components
Ventilator Components
• The minimum operating pressure for wall-supplied air
or oxygen is 35 PSI (Pound per Square Inch); the
maximum is 100 PSI.
1 PSI = 6.89 Kpa = 51.7 mmHg
• Internal preset regulators reduce internal supply
pressure to 10 PSI. The optional compressor produces
a pressure of approximately 10 PSI.
• An automatic gas-supply switching circuit provides for
emergency operation whenever gas supply inlet
pressure or compressor pressure falls below a
prescribed range (this may be less than the minimum
operating pressure).
Ventilator Components
Patient Service Systems
The patient service system consists of:
1) Humidifier circuit, for warming and humidifying the inspiratory
gases.
2) Patient service circuit, for transporting Air from the pneumatic
system to the patient and back to the ventilator
3) Nebulizer circuit, for adding medications to the gas; and
exhalation flow circuit, for monitoring and calculating the volume
of exhaled gas.
4) The system also contains filters in its inspiratory and expiratory
limbs that confine bacterial contamination in the humidifier and
patient service circuit
Ventilator Components
6) A check valve, that prevents reverse gas flow; and an
exhalation valve that seals the system during
inspiration and maintains PEEP.
7) The internal exhalation valve is housed in the
exhalation compartment.
8) Because exhalation compartment components are the
last elements in the expiratory limb (downstream from
the heated exhalation bacteria filter), they don’t need
to be cleaned and sterilized.
Humidifier
Nebulizers
Patient Service Systems
ICU Ventilator
Portable and Transporter
Ventilator
Operating Modes of Mechanical
Ventilation
The ventilator mode can be defined as:
• A set of operating characteristics that control how
the ventilator functions. An operating mode can
be described by the way ventilator is triggered into
inspiration and cycled into exhalation.
• What variables are limited during inspiration, and
whether or not the mode allows only mandatory
breaths, spontaneous breaths, or both?
Operating Modes of Mechanical
Ventilation
Many different functions are commonly available on
modern ventilators regardless of the mode. These
functions include:
1. Control of the FIO2, (FIO2 is the oxygen fraction).
2. Control of the inspiratory flow rate.
3. Control of various alarms.
Operating Modes of Mechanical
Ventilation
• There are 13 essential Ventilator modes available in
different ventilators.
• Two or more of these modes are often used
together to achieve certain desired effects. For
example, spontaneous plus Positive End Expiratory
Pressure (PEEP) is the same as Continuous Positive
Airway Pressure (CPAP).
• Synchronized Intermittent Mandatory Ventilation
(SIMV) may be used with Pressure Support
Ventilation (PSV) to provide ventilation and reduce
the work of breathing.
Operating Modes of Mechanical
Ventilation
The four modes which are the most important in
ventilation & are common on all ventilator
equipment's, which are:
1. Positive End-Expiratory Pressure (PEEP),
2. Continuous Positive Airway Pressure (CPAP).
3. Controlled Mandatory Ventilation (CMV).
4. Synchronized Intermittent Mandatory
Ventilation (SIMV).
Operating Modes of Mechanical
Ventilation
Positive End-Expiratory Pressure (PEEP)
Positive end-expiratory pressure (PEEP) increases
the end-expiratory or baseline airway pressure to a
value greater than atmospheric (0 cm H2O on the
ventilator manometer).
It is often used to improve the patient's
oxygenation status, especially in hypoxemia that is
refractory to increasing FIO2.
Operating Modes of Mechanical
Ventilation
Continuous Positive Airway Pressure (CPAP)
Continuous positive airway pressure (CPAP) is PEEP
applied to the airway of a patient who is breathing
spontaneously.
The indications for CPAP are essentially the same as for
PEEP with the addition requirement that the patient
must have adequate lung functions that can sustain
ventilation documented by the PaCO2.
Operating Modes of Mechanical
Ventilation
Controlled Mandatory Ventilation (CMV)
• With controlled mandatory ventilation or control mode,
the ventilator delivers the preset tidal volume at a timetriggered respiratory rate.
• Since the ventilator controls both the patient's tidal
volume and respiratory rate, the ventilator "controls"
the patient's minute volume.
• In the control mode, a patient cannot change the
ventilator respiratory rate or breathe spontaneously.
For example, if the tidal and respiratory rate of a
ventilator is set at 800 ml and 10 BPM, respectively, the
minute volume will be 8,000 ml.
Main Systems
Ventilator consists of two major systems:
1. Pneumatic system.
2. Electrical system.
The pneumatic system, under control of the
microprocessor in the electrical system, supplies air and
oxygen to the patient system external to the ventilator.
Air for delivery to the patient and to operate the
pneumatic components is provided by an external
supply or by an optional compressor.
Major components of the pneumatic
system
Pneumatic system
• Oxygen is provided by an external supply.
• The primary pneumatics system consists of two
parallel circuits one for oxygen and one for air.
• An important element of the pneumatic system is
the two proportional solenoid valves (PSOLs),
which precisely control the flow delivered to the
patient.
Pneumatic system
• Air and oxygen flow sensors provide feedback, which
is used by the microprocessor to control the PSOLS.
As a result, the ventilator is able to supply air and
oxygen to a patient according to requirements preselected by an operator at the ventilator keyboard.
• The output of mixed air and oxygen passes through a
patient system external to the ventilator; this patient
system may be composed of tubing, filters, a
nebulizer, water traps, and a humidifier.
Pneumatic system
The patient exhales the gas through the opened
exhalation valve. This valve is part of the ventilator in
units equipped with internal exhalation valves.
It is part of the patient system in ventilators without
this internal valve.
Pneumatic system
The pneumatic system is composed of the following
subsystems:
1.
2.
3.
4.
5.
6.
7.
Wall Gas Supply System
Motor Compressor System
Flow Control System
Exhalation System
PEEP/CPAP System
Safety Valve System
Patient System
Wall Gas Supply System
Wall Gas Supply System
• The wall gas supply system delivers air and oxygen from
external supplies to the ventilator and regulates the gas
to pressures usable by the ventilator.
• During inspiration, oxygen from an external supply enters
the ventilator through filters F1 and F2.
• If an external source of compressed air is available, the
air passes through filters F3 and F4.
• Oxygen and air pressure switches PS1 and PS2 continually
monitor these supply lines for pressure loss.
Wall Gas Supply System
Wall Gas Supply System
• The gases then flow through oxygen and air cheek
valves CV1 and CV2.
• These check valves prevent backflow that could
contaminate the wall supply lines.
• Oxygen and air regulators REG1 and REG2 reduce the
supply pressures from between 35 and 100 PSI to 10
PSI nominal.
• Excess REG1 pressure is vented to a common port.
REG2 is vented to atmosphere directly.
Wall Gas Supply System
• If an external source of air is available and of adequate
pressure, this air passes through SOL3 and F7 into the
PEEP/CPAP and safety valve systems.
• If this external air supply be lost, the compressor takes
over.
• If the compressor pressure drops below 8 psi, crossover solenoid SOL3 is energized, supplying pure oxygen
to these systems).
Safety Valve System
Safety Valve System
• The safely valve system, vents (Reliefs) excessive ventilator
pressure.
• The operating pressure of the patient system should not
exceed 120 to 150 cmH2O.
• Components in the safety valve check valve system work
together to relieve the excess pressure.
• The safety valve, piloted by REG4, opens when it senses
pressure above this range.
• REG4, R1, and R2 establish and maintain the pilot pressure to
the safety valve.
Safety Valve System
Safety Valve System
• In case of a catastrophic ventilator failure, such as
a power failure, safety valve solenoid SOL5 is deenergized, the pilot pressure to the safety valve is
reduced to zero, and the safety valve opens.
• This action permits the patient to breath room
air. CV3, which is built into the safety valve,
prevents rebreathing from the room by ensuring
that exhalation occurs only through the
exhalation valve in the patient system.
Exhalation System
Exhalation System
• The exhalation system, filters and monitors the
flow of the patient's exhaled gas.
• The exhalation valve is part of the exhalation
system in ventilators with an internal exhalation
valve.
• In ventilators with an external exhalation valve,
the exhalation valve is part of the patient system.
Exhalation System
Exhalation System
Bacteria Filter Heater
Heats the patient's exhaled gas as it passes through the
exhalation bacteria filter on its way to exhalation flow and
temperature sensors 03/T3.
Exhalation Bacteria Filter
Helps prevent bacteria in the patient's exhaled gas from
being vented to the room air and reduces crosscontamination of the ventilator.
The exhalation bacteria filter captures particles as small as
0.3 g at a flow of 100 lpm with 99.97% efficiency.
•
Exhalation System
Exhalation Flow and Temperature Sensors (Q3/T3)
provides flow information on a patient's exhaled gas.
Q3 measures exhaled gas flows in the range 1 to 200 lpm.
T3 is a thermistor that measures the temperature of the
exhaled gas. Its temperature range is 25 to 50 C .
Exhalation Valve
A pneumatically-actuated valve that closes during
inspiration to prevent delivered gas from venting to
atmosphere.
During exhalation, it opens sufficiently to maintain the
operator-selected PEEP. The exhalation valve is piloted by
the exhalation pilot control solenoid valve, SOL4.
Exhalation System
Operation
As the patient exhales, de-energized exhalation pilot
control solenoid SOL4 provides pressure to pilot the
exhalation valve open to the PEEP level.
This allows the exhaled gas to enter the exhalation
system through the heated filter.
Exhalation System
The heating element surrounding the filter raises the
temperature of the exhaled gas above the dew point to
prevent condensation In Q3.
The heated filter also removes bacteria from the
exhaled gas before the gas is finally vented to
atmosphere through the exhaust vent.
Pneumatic system