The Anaesthesia Machine - 1

Presented by- Dr. Vineet Chowdhary

Moderator- Dr. Avnish Bharadwaj

NO EQUIPMENT IS MORE INTIMATELY ASSOCIATED WITH THE PRACTICE OF

ANAESTHESIOLOGY THAN THE ANAESTHESIA MACHINE 

Anaesthesia WorkstationAn anesthesia workstation integrates most of the components necessary for administration of anesthesia into one unitIt is a device which delivers a precisely-known but variable gas mixture, including anaesthetizing and life-sustaining gases. Consists of:The anesthesia machineVentilatorBreathing systemScavenging system MonitorsAdded to this may be drug delivery systems, suction equipment, and a data management system

HistoryThe original concept of Boyle's machine was invented by the British anaesthetist H.E.G. Boyle in 19171920 – A vapourizing bottle is incorporated

to the machine.1926 – A 2nd vaporizing bottle and by-pass

controls are incorporated.1930 – A Plunger device is added to the

vaporizing bottle.1933 – A dry-bobbin type of flowmeter is

introduced.1937 – Rotameters displayed dry-bobbin

type of flowmeters

Types of Anesthesia MachineIntermittent-Gas flows only during inspiration

Egs: Entonox apparatus, Mackessons apparatus

Continuous-Gas flows both during inspiration and expiration. Egs :

Boyle Machine Forregar Dragger

Standards for Anesthesia Machines and Workstations

Standards for anesthesia machines and workstations provide guidelines to manufacturers regarding their minimum performance, design characteristics, and safety requirements. During the past 2 decades, the progression of anesthesia machine standards has been as follows:

1979: American National Standards Institute 1988: American Society for Testing and Materials, 1994: ASTM F1161-94 (reapproved in 1994 and

discontinued in 2000) 2005: International Electrical Commission (IEC) 2005: ASTM (reapproved)F1850 European standard is EN740

Contd….

To comply with the 2005 ASTM F1850-00 standard, newly manufactured workstations must have monitors that measure the following parameters:

continuous breathing system pressure, exhaled tidal volume, ventilatory CO2 concentration, anesthetic vapor concentration, inspired oxygen concentration, oxygen supply pressure, arterial hemoglobin oxygen saturation arterial blood pressure, and continuous electrocardiogram.

Contd…

The anesthesia workstation must have a prioritized alarm system that groups the alarms into three categories: high, medium, and low.

These monitors and alarms may be enabled automatically and made to function by turning on the anesthesia workstation, or the monitors and alarms can be enabled manually and made functional by following a pre-use checklist.

Basic Schematics

System components

Electrical Pneumatic

1.Master Switch2.Power Failure Indicator3.Reserve Power4.Electrical Outlet5.Circuit Breakers6.Data Communication Port

1.High Pressure System2.Intermediate System3.Low Pressure System

Electrical ComponentsMaster Switch

Master (main power) switch activates both the pneumatic and electrical functions . On most machines, when the master switch is in the OFF position, the only electrical components that are active are the battery charger and the electrical outlets

Standby position - allows the system to be powered up quickly

Computer-driven machines should be turned OFF and restarted with a full checkout at least every 24 hours.

STANDBY mode is not used for an extended period.

Most machines are equipped with a visual and/or audible indicator to alert the anesthesia provider to the loss of mains power .The machine will usually give an indication when mains power is lost.

Power Failure Indicator

Reserve PowerBackup source of power for the occasional outage is necessary. The anesthesia provider should check the battery status during the preuse checkout procedure.While some older anesthesia machines used replaceable batteries, most new machines use rechargeable batteries.It usually takes a number of hours to fully recharge a battery after it has completely discharged.

Electrical Outlets Most modern anesthesia machines have electrical

outlets. These are intended to power monitors and other

devices. As a general rule, these outlets should only be used

for anesthesia monitors. Other appliances should be connected directly to

mains power.

Next to each outlet is a circuit breaker.

There are circuit breakers for both the anesthesia machine and the outlets .When a circuit breaker is activated, the electrical load should be reduced and the circuit breaker reset

Circuit Breakers

Data Communication Ports Most modern anesthesia machines have

data communications ports. These are used to communicate between

the anesthesia machine, monitors, and the data management system

Gases are supplied under tremendous pressure for the convenience of storage and transport.

The anaesthesia machine receives medical gases from a gas supply; controls the flow of desired gases reducing their pressure, to a safe level.

So the pressure inside a source ( cylinder or pipeline ) must be brought to a certain level before it can be used for the purpose of ventilation.

And it needs to be supplied in a constant pressure, otherwise the flow meter would need continous adjustment.

.

This is achieved by bringing down the pressure of a gas supply in a graded manner with the help of three pressure reducing zones .

Thus the pneumatic part of the machine can be conveniently divided into three parts- high ,intermediate and low pressure systems

• Consists of:Consists of:– Hanger YolkHanger Yolk – Check valve Check valve

– Cylinder Cylinder Pressure Pressure Indicator Indicator (Gauge)(Gauge)

– Pressure Pressure Reducing Reducing Device Device (Regulator)(Regulator)

• Usually not Usually not used, unless used, unless pipeline gas pipeline gas supply is offsupply is off

Hanger Yoke Assembly The Hanger yoke assembly

1) Orients and supports the cylinder

2) Provides a gas-tight seal

3) Ensures uni-directional gas flow

The workstation standard recommends that there be at least one yoke each for oxygen and nitrous oxide.

If the machine is likely to be used in locations that do not have piped gases, it is advisable to have a double yoke, especially for oxygen.

BODY It is threaded into the frame of the machine.

It provides support for the cylinder(s).

Commonly the swinging gate type is used.

When a cylinder is mounted onto or removed from a yoke, the hinged part can be swung to side.

RETAINING SCREW It is threaded into the distal end of the yoke.

Tightening the screw presses the outlet of the cylinder valve against the washer and the nipple so that a gas tight seal is obtained.

The cylinder is then supported by the retaining screw, the nipple, and the index pins.

The conical point of the retaining screw is shaped to fit the conical depression on the cylinder valve.

NippleNipple

It is a part of the yoke It is a part of the yoke through which the gas enters through which the gas enters the machine.the machine.

It fits into the port of It fits into the port of the cylinder valve.the cylinder valve.

If it is damaged, it may be If it is damaged, it may be impossible to obtain a tight impossible to obtain a tight seal with the cylinder seal with the cylinder valvevalve..

These are situated below the nipple.

These help to prevent mounting of incorrect cylinder to yoke.

The holes into which the pins are fitted must be of a specific depth.

If they extend too far into the body of the yoke, it may be possible to mount a incorrect cylinder.

INDEX PINS

Bodok seal-cylinders are fitted with yoke with a sealing washer called BODOK SEAL

-it is made up of non combustible material and has a metal periphery which make it long lasting.

-it should be less than 2.4mm thick prior to compression.

-only one seal should be use between the valve & yoke

Caution!!The wrong Cylinder may be fitted by:

1.Using extra sealing washers2.Removing of/ Wearing of the Index Pins3.Placing an inverted gas cylinder

FilterIt is used to prevent particulate matter from entering the machine.

It is to be placed between the cylinder and the pressure reducing device.

FILTER

Placing cylinder in yoke

Placing a Cylinder in a Yoke1.Cylinder valves and yokes not be contaminated with oil or grease2. Persons placing a cylinder in a yoke should always wash their hands first3. Pin Index Safety System pins are present4.Retract the retaining screw5. The washer is placed over the nipple6.The cylinder is supported by the foot and guided into place manually 7. The port on the cylinder valve is guided over the nipple

and the index pins engaged in the appropriate holes8. The retaining screw is tightened 9. Do not insert the screw in the safety relief device10. Make certain that the cylinder is full and that there is no leak

CHECK VALVE ASSEMBLY

It allows gas from a cylinder to enter the machine but prevents gas from exiting the machine when there is no cylinder in the yoke.

It allows an empty cylinder to be replaced with a full one without having to turn off the `in–use` cylinder.

Prevents transfer of gas from one cylinder to the other with a lower pressure in a double yoke.

It consists of a plunger that slides away from the side of the greater pressure.

It is not designed to act as a permanent seal for empty yoke and may allow small amount of gas to escape.

As soon as a cylinder is exhausted it should be replaced by a full one or a dummy plug.

In order to minimize losses –

Yokes should not be left vacant for extended periods

An empty cylinder should be replaced as soon as possible

An yoke plug can be used to prevent gas leak or

An empty cylinder can be left behind after closing the

valve

A Bourdon tube is a hollow metal tube(copper alloy) bent into a curve, then sealed on one side and linked to a clock like mechanism

Safety features in Cylinder Pressure Indicator

Gauge is usually color coded.Name and symbol of gas are written over dial.If bourdon tube ruptures gas is vented from back side Gauges are angled and placed in such a way that it can be easily read by anesthetist.Instructions like “use no oil’’ “open the valve slowly’’ are written on the gauge

Electronic Cylinder Pressure IndicatorLight emitting diodes(LED’S)in electronic pressure gauge indicateCylinder valve is close –Dark colorCylinder valve is open –

Pressure adequate –Green Pressure inadequate-Red

PRESSURE REDUCING DEVICE (REGULATOR)

The pressure in a cylinder varies. The anesthesia machine is fitted with devices (reducing valves, regulators, reducing regulators, reduction valves, regulator valves) to maintain constant flow with changing supply pressure.

These reduce the high and variable pressure found in a cylinder to a lower (40 to 48 psig, 272 to 336 kPa) and more constant pressure suitable for use in an anesthesia machine.

The machine standard requires reducing devices for each gas supplied to the machine from cylinders.

Physical Principle- A large pressure acting over a small area is balanced by a small pressure over a larger area

Pressure regulators have safety relief valvesIf due to any reason there is build up of pressure in pressure regulator then the safety valve blow off at a set pressure of 525 k pa(70psi)

Safety features on pressure regulator

INTERMEDIATE  PRESSURE  SYSTEMBegins at the regulated cylinder supply source at 45 psig includes the pipeline sources at 50 to 55 psig and extends to the flow control valve.

Consists of:Pipeline inlet connectionsPipeline pressure indicatorsPipingGas power outletMaster switchOxygen pressure failure devicesOxygen flushAdditional reducing devicesFlow control valves

Check valve

MASTER SWITCH (PNEUMATIC COMPONENT ) The pneumatic portion of the master switch is located

in the intermediate pressure system downstream of the inlets for the cylinder and pipeline supplies

The oxygen flush is usually independent of this switch.

The master switch may be a totally electronic switch that when activated controls the various pneumatic components in the anesthesia machine.

When the master switch is turned off ,the pressure in the intermediate system will drop to zero

PIPELINE INLET CONNECTIONS It is the entry point for gases from the pipelines. The anesthesia workstation standard requires pipeline

inlet connections for oxygen and nitrous oxide. Most machines also have an inlet connector for air. These inlets are fitted with threaded non

interchangeable Diameter Index Safety System (DISS) fittings

A unidirectional (check) valve prevents reversed gas flow from the machine into the piping system

Each pipeline inlet is required to have a filter with a pore size of 100μm or less. The filter may become clogged, resulting in a reduction in gas flow.

PIPELINE INLET CONNECTIONS

PIPELINE PRESSURE INDICATORS Indicators to monitor the pipeline pressure of each

gas are required by the anesthesia workstation standard.

They are usually found on a panel on the front of the machine and may be color coded for the gases that they monitor

The workstation standard requires that the indicator be on the pipeline side of the check valve in the pipeline inlet.

If the indicator is on the pipeline side of the check valve, it will monitor pipeline pressure only. If the hose is disconnected or improperly connected, it will read “0” even if a cylinder valve is open

If the indicator were on the machine (downstream) side of the check valve, it would not give a true indication of the pipeline supply pressure unless the cylinder valves were closed. If a cylinder valve is open and the pipeline supply fails, there will be no change in the pressure on the indicator until the cylinder is nearly empty.

Pipeline pressure indicators should always be checked before the machine is used. The pressure should be between 50 and 55 psig (345 and 380 kPa). The indicators should be scanned repeatedly during use.

Piping is used to connect components inside the machineIt must be able to withstand four times the intended service pressureLeaks between the pipeline inlet or cylinder pressure reducing system and the flow control valve not exceed 25 mL/minuteIf the yoke and pressure reducing system are included, the leakage may not exceed 150 mL/minute.

PIPING

Some machines have a gas selector switch that prevents air and nitrous oxide from being used together.

GAS SELECTOR SWITCH

GAS POWER OUTLETOne or more gas power (auxiliary gas) outlets may be present on an anesthesia machine. It may serve as the source of driving gas for the anesthesia ventilator or to supply gas for a jet ventilator. Either oxygen or air may be used.The ventilator is an integral part of the modern machine and the breathing system and is connected to the ventilator with internal piping. Therefore, the power outlet is not found in many anesthesia machines today.

OXYGEN PRESSURE FAILURE DEVICES

One of the most serious mishaps that occurred with early machines was depletion of the oxygen supply (usually from a cylinder) without the user awareness.

The result was delivery of 100% anesthetic gas. Numerous inventions have been devised to prevent this

Oxygen Failure Safety Device

Oxygen Supply Failure Alarm

Pressure Sensor Shut-off Valve: Datex OhmedaPressure Sensor Shut-off Valve: Datex Ohmeda

Operates in a threshold manner: either open or shutOxygen pressure moves the piston and pin upward and the valve opens for N2OWhen pressure of oxygen falls below preset value, force of the valve return spring completely closes the valve

Oxygen Failure Protection Device: DragerBased on a proportioning principle rather than a threshold principlePressure of N2O falls in Propotion of decrease of Oxygen.Total cutoff seen at <12psig.Seat nozzle assembly connected to a spring loaded conical tapered piston

Oxygen Supply Failure Alarm

ASTM standard specifies that whenever the oxygen supply  pressure falls below a certain threshold (usually 30 psig), alarm must get activated within 5 seconds. It should not be possible to disable this alarmThey aid in preventing hypoxia caused by problems occurring upstream in the machine circuitry (disconnected oxygen hose, low oxygen pressure in the pipeline, and depletion of oxygen cylinders)

CAUTION!!

These devices do not offer total protection against a hypoxic mixture being delivered, because they do not prevent anesthetic gas from flowing if there is no flow of oxygen.

Equipment problems (such as leaks) or operator errors (such as a closed or partially closed oxygen flow control valve) that occur downstream are not prevented by these devices.

They do not guard against accidents from crossovers in the pipeline system or a cylinder containing the wrong

gas.

Second-stage Pressure RegulatorSecond-stage Pressure RegulatorSome machines have pressure regulators in the intermediate pressure system just upstream of the flow indicatorsReduce the pressure further to around 26 psi (177 kPa) for nitrous oxide and 14 psi (95 kPa) for oxygenThe purpose of this pressure regulator is to eliminate fluctuations in pressure supplied to the flow indicatorsBy reducing the pressures below the normal fluctuation range, the flow will remain more constant. Not all anesthesia machines are equipped with this device.

OXYGEN FLUSH The oxygen flush (oxygen bypass, emergency oxygen

bypass) receives oxygen from the pipeline inlet or cylinder pressure regulator and directs a high unmetered flow directly to the common gas outlet.

It is commonly labeled “02+.” On most anesthesia machines, the oxygen flush can be

activated regardless of whether the master switch is turned ON or OFF.

A flow between 35 and 75 L/minute must be delivered. The button is commonly recessed or placed in a collar

to prevent accidental activation.

It consists of a button and stem It consists of a button and stem connected to a spring loaded connected to a spring loaded ball .The ball is in contact with the ball .The ball is in contact with the seat .When the button is depressed, seat .When the button is depressed, the ball is forced away from the the ball is forced away from the seat , allowing the oxygen to flow to seat , allowing the oxygen to flow to the outlet. A spring opposing the the outlet. A spring opposing the ball will close the valve when the ball will close the valve when the button is not depressed . Delivers button is not depressed . Delivers oxygen at 60 psig.oxygen at 60 psig.

Reported hazards associated with the oxygen flush include

Accidental activation – causing oxygen-enriched gas mixture, anaesthetic dilution

The flush valve stuck in the ON position Barotrauma and awareness during anesthesia Internal leakage

The anesthesia workstation standard requires that the connection of the flush valve delivery line to the common gas outlet be designed so that activation does not increase or decrease the pressure at the vaporizer outlet by more than 10 kPa or increase the vapor output by more than 20%.

FLOW ADJUSTMENT CONTROL Controls flow of gas through it’s associated indicator by manual adjustment of a variable orificeCurrent standard requires that there be only one flow control for each gas. It must be adjusted or identifiable with its flow indicator

CONTROL KNOBCONTROL KNOBTouch and colour coded

Joined to stem

Large enough to be turned easily

ROTATORY STYLE KNOBSROTATORY STYLE KNOBSOxygen knob- Fluted Profile, as large/ larger than any other gas knobKnobs turned counter clockwise- increase flowKnobs turned clockwise- decrease flowAll other knobs should be roundOxygen knobs must look and feel different than other knobsThey should operate smoothlyKnob should not be over turned during closure because further tightening may damage the pin/seat

CAUTION!!CAUTION!!Loose or worn knobs may respond to light touch or accidental brushingLeakage through open flow control valvesInability to turn the knobFailure to allow adequate gas flow