Mechanical Ventilator 4th Lecture Mechanical Ventilator Part Two

Ventilator Block Diagram (1-2) The main components of the ventilator 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). Pneumatic system: System That mixes the gases, generates flow waveforms, delivers volumes, and measure pressures. Patient service systems: System that routes the mixed gases to and from the patient.

Ventilator Block Diagram (2-2) 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. 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: Humidifier circuit, for warming and humidifying the inspiratory gases. Patient service circuit, for transporting Air from the pneumatic system to the patient and back to the ventilator Nebulizer circuit, for adding medications to the gas; and exhalation flow circuit, for monitoring and calculating the volume of exhaled gas. The system also contains filters in its inspiratory and expiratory limbs that confine bacterial contamination in the humidifier and patient service circuit

Ventilator Components A check valve, that prevents reverse gas flow; and an exhalation valve that seals the system during inspiration and maintains PEEP. The internal exhalation valve is housed in the exhalation compartment. 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: Control of the FIO2, (FIO2 is the oxygen fraction). Control of the inspiratory flow rate. 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: Positive End-Expiratory Pressure (PEEP), Continuous Positive Airway Pressure (CPAP). Controlled Mandatory Ventilation (CMV). 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 time-triggered 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.

Operating Modes of Mechanical Ventilation Synchronized Intermittent Mandatory Ventilation (SIMV) Synchronized intermittent mandatory ventilation (SIMV) is a mode in which the ventilator delivers either assisted breaths to the patient at the beginning of a spontaneous breath or time triggered mandatory breaths. The mandatory breaths are synchronized with the patient’s spontaneous breathing efforts so as to avoid breath stacking.

Main Systems Ventilator consists of two major systems: Pneumatic system. 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 pre-selected 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: 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, cross-over 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 de-energized, 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 cross-contamination 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