AN APPROACH TO ANAESTHESIA WORKSTATION

MODERATORS:

DR.B.SOWBHAGYA LAKSHMI,MDPROFESSOR IN DEPT. OF ANAESTHESIOLOGY

DR.KRISHNA PRASAD,MDASSISTANT PROFESSOR

PRESENTED BY DR.SIRISHA ANAPARTHI PG IN ANAESTHESIOLOGY

• NO EQUIPMENT IS MORE INTIMATELY ASSOCIATED WITH THE PRACTICE OF ANAESTHESIOLOGY THAN THE

ANAESTHESIA MACHINE

THE ANAESTHESIA MACHINE

The anaesthesia machine is a device which delivers a precisely-known but variable gas mixture, including anaesthetizing and life-sustaining gases.

HISTORY

• The original concept of Boyle's machine was invented by the British anaesthetist H.E.G. Boyle in 1917. Prior to this time, anaesthetists often carried all their equipment with them, but the development of heavy, bulky cylinder storage and increasingly elaborate airway equipment meant that this was no longer practical for most circumstances. The anaesthetic machine is usually mounted on anti-static wheels for convenient transportation.

HISTORY :• 1917 – Boyle machine with a water sightfeed type of flowmeter is introduced byHenry Edmund Gaskin Boyle.• 1920 – A vapourizing bottle is incorporatedto the machine.• 1926 – A 2nd vaporizing bottle and by-passcontrols are incorporated.• 1930 – A Plunger device is added to thevaporizing bottle.• 1933 – A dry-bobbin type of flowmeter isintroduced.• 1937 – Rotameters displayed dry-bobbintype of flowmeters

Anesthetic Machines• Anesthetic machines began appearing at the end of the 19th century • Early anesthetic machines were utilized in dental anesthesia for

administration of N2O and O2 • Initial machines were either:

• Continuous flow – continuous flow throughout inspiration and expiration (eg. Heidbrink, Foregger, Boyle)

• Intermittent flow – flow of gas during inspiration only (eg. McKesson)

• Machines evolved to incorporate reducing valves, flow meters, vaporizers and circuits with carbon dioxide absorption

Boyle Anesthesia Apparatus c. 1920• Modification of original machine

developed by Dr. Henry Boyle in 1917• Coxeter dry flow meter allowed

proportioning of O2, CO2 & N2O

• Two glass vaporizing bottles • Bottom illustrations:

– Case with accessories– Machine stand with four cylinder

yokes (2 each for N2O and O2) + carrying handle

116a, 117

Foregger Metric Gas Machine Montreal Model c. 1924

• Modification of Richard von Foregger’s original metric gas machine for use with cyclopropane

• Eliminated reserve gas tanks, with exception of O2, because of the increased use of CO2 absorbers

• “Wet flowmeters” used water displacement to provide accurate measurement while introducing humidity to reduce the risks of interior static

23

Water’s Cannisters(Waters “to and fro”) c. 1930

• Ralph M Waters began experiments with CO2 absorption in 1915

• Developed “to and fro” system through which inspired and expired gases were directed

• Metal cylinder was packed with absorbent alkaline granules resulting in economy of gas use along with heat and moisture conservation

109 a-c

McKesson Nargraf Machine(Model H) c. 1920

• Modification of Dr. E I McKesson’s Model A machine of 1910

• Reducing valves admit N2O and O2 into two bags enclosed in metal drums at equal pressures

• Gases pass to percentage mixing chamber with proportion controlled by dial

• Intermittent flow is dependant upon patients inspiration

119

Heidbrink Apparatus (mixing head only) c. 1930

• Modification of Dentist Jay Heidbrink’s original apparatus introduced in 1912 for administration of N2O and O2 primarily for dental anaesthesia

• Proportioning device and valves reduced cylinder pressure of tank gases to working pressures

143

Midget Kinet-O-Meter c. 1940

• Modification of Dr. Heidbrink’s earlier apparatus to administer N2O / O2 for dental anesthesia

• Flow meter panel calibrated for oxygen, nitrous oxide and cyclopropane along with four cylinder yokes (two each for O2 and N2O)

• Mounted on a pole to which chart stand support is attached

118

OUTLINE• The Machine• Gas Supply Systems: Hospital pipeline Cylinder• High Pressure System (exposed to cylinder pressure)• Intermediate Pressure System (exposed to pipeline press)• Low Pressure System (distal to flowmeter needle valve)• Circle System CO2 Absorber System

Unidirectional Valves• Ventilator• Scavenger System

The MachineOhmeda N.A.Drager (Narkomed)

Anesthesia Machine: Jackson Memorial Hospital

vaporizerbellow

Corrugated tube

Soda lime

Flow meter

ventilator

APL valve

Scavenging system

Basic Schematics

The Anesthesia Machine

High Intermediate Low Pressure Circuit

PNEUMATIC SYSTEM1. HIGH PRESSURE a. Hanger Yoke b. Power Failure Indicator c. Pressure Regulators

2. INTERMEDIATE PRESSURE SYSTEM a. Master Switch (Pneumatic component) b. Pipeline Inlet Connections c. Pipeline Pressure Indicators d. Piping e. Gas Power Outlet f. Oxygen Pressure Failure Devices g. Gas Selector Switch h. Second-Stage Pressure Regulator i. Oxygen Flush j. Flow Adjustment Control

3. LOW PRESSURE SYSTEM a. Flowmeters b. Hypoxia Prevention Safety

Devices c. Unidirectional (Check) valve d. Pressure Relief Device e. Low-Pressure Piping f. Common (fresh) Gas Outlet

4.ALTERNATIVE OXYGEN CONTROL

Gas Supply SystemsHospital Pipeline

Pipeline Trouble

• Pipeline sources are not trouble free: contamination (particles, bacteria, viral, moisture), inadequate pressure, excessive pressures, and accidental crossover (switch between oxygen and some other gas such as nitrous oxide or nitrogen) are all reported.

DISS

• Pipeline inlets are connected with DISS (diameter index safety system) non-interchangeable connections.

• The check valve, located down stream from the pipeline inlet, prevents reverse flow of gases (from machine to pipeline, or to atmosphere), which allows use of the gas machine when pipeline gas sources are unavailable.

PISS

PISS (pin-index safety system) prevents misconnection of a cylinder to the wrong yoke. Keep cylinders closed except when checking machine, or while in use (if O2 from pipeline is unavailable)

Diagram showing the index

positions of a cylinder valve.

Oxygen: 2 & 5Nitrous oxide: 3 &

5Air: 1 & 5

CO2: 1 & 6

Color coding of medical gas cylinders and their pressure when full

Name of the gas Body colour Shoulder colour Pressure (kPa)(At room temp)

Oxygen Black White 13700

Nitrous Oxide Blue Blue 4400

Carbon dioxide Grey Grey 5000

Air Grey White/black quarters

13700

Entonox Blue White/blue quarters 13700

Oxygen/helium Black White/brown quarters

13700

LAPSE IN MAINTENANCE

Sudbury Ontario in the 1970s: 23 people died because the N20 and O2 pipelines were crossed over during repairs

Gas Supply SystemsCylinder

Pin Index Safety System:

O2 2,5

N2O 3,5

High Pressure System(parts which receive gas at cylinder pressure) • hanger yoke (including filter and unidirectional

valve) • yoke block (with check valves) • cylinder pressure gauge • cylinder pressure regulators

Hanger Yoke & Check Valve

Hanger Yoke– orients cylinders– provides

unidirectional flow – ensures gas-tight

seal.

Check Valve– minimize trans-

filling– allows change of

cylinders during use– minimize leaks to

atmosphere if a yoke is empty.

CHECK VALVES

The check valve, located down stream from the pipeline inlet, prevents reverse flow of gases (from machine to pipeline, or to atmosphere), which allows use of the gas from cylinder when pipeline gas sources are unavailable.

Check Valve

CYLINDERS• The cylinder pressure regulator converts high,

variable cylinder pressure to a constant pressure of approximately 45 psi downstream of the regulator.

• This is intentionally slightly less than pipeline pressure, to prevent silent depletion of cylinder contents if a cylinder is inadvertently left open after checking its pressure.

• Cylinder pressure gauge indicates pressure in the higher-pressure cylinder only (if two are opened simultaneously).

Anesthesia Components

• Anesthesia Machine– Frame

– Regulator• Placed on O2 tanks to decrease pressure from

tank• 2 types of tanks

– “E” Tanks» 650L @ 1800PSI

– “H” Tanks» 7100L @ 2200PSI

• Output pressureadjusted with knob

E cylinder Characteristics

Gas US (International) PSI Capacity (L) PISS O2 Green (white) 1900 660 2-5 N2O Blue (blue) 745 1590 3-5 Air Yellow (B & W) 1900 625 1-5

**** We’ll use 2000psi for O2 instead of 1900psi****

HOW LONG BEFORE O2 TANK IS EXHAUSTED???

-The time to exhaustion is calculated by dividing the remaining O2 volume in the cylinder by the rate of consumption of O2. -Remaining volume in liters (L) in an E-cylinder is calculated by dividing the cylinder pressure in psig by 2000 psig and multiplying by 660 L.

EXAMPLE

• If cylinder gauge reads 1,000 psig, this represents (1000/2000) X 660 = 330 L left in that tank. The rate of consumption of O2 during mechanical ventilation is the sum of the O2 flow meter setting and the patient’s minute ventilation (VT in L x RR in breaths/min).

• If FGF is 0.5 L/min O2 and 1.0 L/min N2O and VT is 0.7 L and RR is 10 bpm, then the minute ventilation is 7 L/min (0.7L x 10 bpm)

* The total O2 consumption is 7.5 L/min. The expected time to exhaustion is thus approximately 330 L divided by 7.5 L/min = 44 min (ignoring the gas sampled by the gas analyzer and leaks)

Intermediate Pressure System

Machine piping “guts”

Gauges-pipeline (intermediate press. )

Hospital Pipeline Outlets

Hospital Pipeline Inlets

Intermediate Pressure System(receives gases at low, relatively constant pressures (37-55

psi, = pipeline pressure)(*For consistency we’ll use 50 psi) – pipeline inlets and pressure gauges – ventilator power inlet – Oxygen pressure-failure device (fail-safe) and alarm – flowmeter valves – oxygen second-stage regulator – oxygen flush valve

OXYGEN PRESSURE FAILURE DEVICES

• A Fail-Safe valve is present in the gas line supplying each of the flowmeters except O2. This valve is controlled by the O2 supply pressure and shuts off or proportionately decreases the supply pressure of all other gasses as the O2 supply pressure decreases

• Historically there are 2 kinds of fail-safe valves– Pressure sensor shut-off valve (Ohmeda)– Oxygen failure protection device (Drager)

OXYGEN PRESSURE FAILURE DEVICES

Machine standard requires that an anaesthesia machine be designed so that whenever the oxygen supply pressure is reduced below normal, the oxygen concentration at the common gas outlet does not fall below 19%

PRESSURE SENSOR SHUT-OFF VALVE

• Oxygen supply pressure opens the valve as long as it is above a pre-set minimum value (e.g. 20 psig).

• If the oxygen supply pressure falls below the threshold value the valve closes and the gas in that limb (e.g. N2O) does not advance to its flow-control valve.

Pressure Sensor Shut-Off Valve

OXYGEN FAILURE PROTECTION DEVICE (OFPD)

• Based on a proportioning principle rather than a shut-off principle

• It shuts off or proportionately decreases & ultimately interrupts supply of N2O if O2 supply pressure decreases

• The pressure of all gases controlled by the OFPD will decrease proportionately with oxygen pressure.

Oxygen Failure Protection Device (OFPD)

OXYGEN SUPPLY FAILURE ALARM

• The machine standard specifies that whenever the oxygen supply pressure falls below a manufacturer-specified threshold (usually 30 psig), a medium priority alarm shall blow within 5 seconds.

Limitations of Fail-Safe Devices/Alarms

• Fail-safe valves do not prevent administration of a hypoxic mixture because they depend on pressure and not flow.

• These devices do not prevent hypoxia from accidents such as pipeline crossovers or a cylinder containing the wrong gas

Contd.

• These devices prevent hypoxia from some problems occurring upstream in the machine circuit (disconnected oxygen hose, low oxygen pressure in the pipeline and depletion of the oxygen cylinder)

• Equipment problems that occur downstream (for example leaks or partial closure of the oxygen flow control valve) are not prevented by these devices.

Oxygen Flush Valve (O2+)

• Receives O2 from pipeline inlet or cylinder reducing device and directs high, unmetered flow directly to the common gas outlet (downstream of the vaporizer)

• Machine standard requires that the flow be between 35 and 75 L/min

• The ability to provide jet ventilation

• Hazards– May cause barotrauma– Dilution of inhaled anesthetic

Second-Stage Reducing Device

• Located just upstream of the flow control valves

• Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further to 26 psig for N2O and 14 psig for O2

• Purpose is to eliminate fluctuations in pressure supplied to the flow indicators caused by fluctuations in pipeline pressure

LOW PRESSURE SYSTEM

• Extends from the flow control valves to the common gas outlet

• Consists of:– Flow meters– Vaporizer mounting device– Check valve– Common gas outlet

Flowmeters

-Thorpe tube is an older term for flowmeters. -Components: needle valve, indicator float, knobs, valve stops. -Flow increases when the knob is turned counterclockwise (same as vaporizers). -At low flows, the annular-shaped orifice around the float is (relatively) tubular so (according to Poiseuille's Law) flow is governed by viscosity. (laminar flow)-At high flows (indicated on the wider top part of the float tube), the annular opening is more like an orifice, and density governs flows. (turbulent flow)

Low Pressure System• Distal to Flowmeter Needdle Valve Flow Meters- measures and indicates the rate of gas flowing through it.

Variable orifice/Thorpe tube-constant press. flow meters. Rate of flow r/t: 1) pressure drop across the constriction

2) size of annular opening 3) Physical properties of the gas

(viscosity and density)

Indicator, float or bobbin- 1) rotometers

2) non-rotating floats 3) ball floats Sequence of flowmeters tubes is very

important to decrease chance of hypoxic mixture., Gas flow is from left to right, O2 on right side.

Any leak in flowmeters will vent other gas out or entrain air before O2 is added to gas mixture decreasing

chance that O2 will be lost or diluted.

FLOW

Flowmeter assembly

• When the flow control valve is opened the gas enters at the bottom and flows up the tube elevating the indicator

The indicator floats freely at a point where the downward force on it (gravity) equals the upward force caused by gas molecules hitting the bottom of the float

Arrangement of the Flow-Indicator Tubes

• In the presence of a flowmeter leak (either at the “O” ring or the glass of the flow tube) a hypoxic mixture is less likely to occur if the O2 flowmeter is downstream of all other flowmeters

• In A and B a hypoxic mixture can result because a substantial portion of oxygen flow passes through the leak, and all nitrous oxide is directed to the common gas outlet

* Note that a leak in the oxygen flowmeter tube can cause a hypoxic mixture, even when oxygen is located in the downstream position

CONTD………………………….

• Needle valve can be damaged if it is closed with force

• Flowtube (Thorpe tube) is tapered (narrower at bottom) and gas-specific

• If gas has 2 tubes, they are connected in series with a single control valve

CONTD……………………………• Care of flowmeters includes ensuring that:

– floats spin freely– qualified service personnel regularly maintain gas

machines – an O2 analyzer used always (of course, the readings are

erroneous during use of nasal cannula) – one never adjusts a flowmeter without looking at it – one includes flowmeters in visual monitoring sweeps– one turns flowmeters off before opening cylinders,

connecting pipelines, or turning machine "on".

Proportioning Systems

– Mechanical integration of the N2O and O2 flow-control valves

– Automatically intercedes to maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1

Low Pressure SystemSafety Devices-Purpose is to decrease risk of hypoxic mixture

* Mandatory Minimum O2 Flow- factory preset minimum O2 flow that always flows when machine is on.

* Minimum O2/N2O Ratio– 1:3Device or proportioning system: Flow valves linked

mechanically or pneumatically so O2 cannot be set below 25%.Alarm will signal if O2/NO2 ratio falls below preset value

* O2/NO2 Proportioning Device-Automatically mixes O2 and NO2 to setting selected on dial

Hypoxic breathing is POSSIBLE

• hypoxic guard systems CAN permit hypoxic breathing mixtures IF: – wrong supply gas in oxygen pipeline or cylinder, – defective pneumatic or mechanical components, – leaks exist downstream of flow control valves, or – if third inert gas (such as helium) is used.

SAFETY MECHANISMS IN LOW PRESSURE SYSTEM

• Oxygen must enter the common manifold downstream to other gases

• It prevents hypoxia in event of proximal gas leak

• Oxygen concentration monitor and alarm prevent administration of hypoxic gas mixtures in event of a low-pressure system leak, thus precisely regulating oxygen concentration

Safety in flowmeter subassembly

• Each flowmeter is housed in an independent, colour coded pin specific module

• Oxygen flowmeter is placed downstream• Backpressure check valve• Link device• Backlight display

FLOW CONTROL VALVE ASSEMBLY

• Oxygen flow control valve is physically distinguishable from other gas knobs

• It projects beyond control knob of other gases• Its diameter is larger• Placement of knobs at a distance• All are colour coded

HYPOXIA PREVENTION SAFETY DEVICES

• Mechanical integration of the N2O and O2 flow-control valves

• Automatically intercedes to maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1

LIMITATIONS OF THE SYSTEM

• Machines equipped with proportioning systems can still deliver a hypoxic mixture under the following conditions:– Wrong supply gas– Defective pneumatics or mechanics (e.g. the Link-25

depends on a properly functioning second stage regulator)

– Leak downstream (e.g. broken oxygen flow tube)– Inert gas administration: Proportioning systems

generally link only N2O and O2

Low Pressure System Vaporizers- Classification:

A. Method of regulating output concentration 1. Concentration calibrated

2. Measured flowB. Method of

vaporization 1. Flow over

2. Bubble Through 3. Injection

C. Temperature compensation 1. Thermocompensation 2. Supplied heat

D. Specificity 1.

Agent specific 2. Multiple agent E. Resistance

1. Plenum 2. Low resistance

VAPORIZERS

• Vapor Pressure (VP) Molecules escape from a volatile liquid to the vapor phase, creating a “saturated vapor pressure” at equilibrium

• VP is independent of Atmospheric Press• VP increases with Temperature• VP depends ONLY on the Physical Characteristics of

the Liquid & on its Temperature

CLASSIFICATION

• Variable bypass Fresh gas flow from the flowmeters enters the inlet of any vaporizer which is on. The concentration control dial setting splits this stream into bypass gas (which does not enter the vaporizing chamber), and carrier gas (also called chamber flow, which flows over the liquid agent)

CLASSIFICATION

• Flow over Carrier gas flows over the surface of the liquid volatile agent in the vaporizing chamber (as opposed to bubbling up through it (as in the copper kettle and Vernitrol)

CLASSIFICATION

Temperature compensated Equipped with automatic devices that ensure steady vaporizer output over a wide range of ambient temperatures

Agent-specific Only calibrated for a single gas, usually with keyed fillers that decrease the likelihood of filling the vaporizer with the wrong agent

Out of circuit As opposed to (much) older models such as the Ohio

#8 (Boyle's bottle) which were inserted within the circle system.

Vaporizer Interlock Mechanism

Safety mechanism that allows ONLY one vaporizer at a time to be opened

VAPORIZERS – SAFETY MECHANISMS

• Arrangement of vaporizers on back bar• Colour coded, agent specific key filling system• Interlock device• Select-a-tec system• Firmly secured

VAPORIZER INTERLOCK MECHANISM

Safety mechanism that allows ONLY one vaporizer at a time to be opened

Circle SystemCircle System- CO2 absorber housing and absorber, unidirectional valves, inspiratory and expiratory ports, fresh gas inlet, APL valve, pressure gauge, breathing tubes, Y-piece, reservoir bag, bag/vent switch selector, respiratory gas monitor sensor.

The Circuit: Circle System• Arrangement is variable, but to

prevent re-breathing of CO2, the following rules must be followed:

– Unidirectional valves between the patient and the reservoir bag

– Fresh-gas-flow cannot enter the circuit between the expiratory valve and the patient

– Adjustable pressure-limiting valve (APL) cannot be located between the patient and the inspiratory valve

Circle System• CO2 Absorber System: Housing (canister support), Absorbent, baffles, side tube • Unidirectional Valves-aka Flutter valves, one way valves, check valves, directional valves,

dome valves• Canister-Air space 50%, void space 42%, pore space 8%

– Soda Lime: 4% Sodium Hydroxide, 1% potassium hydroxide, 14-19% H2O, and calcium hydroxide to make 100%, Silica and kielselguhr for hardness

Indicator for color change with exhaustion of CO2 absorption capabilitiesCO2+H2OH2CO32NaOH+2H2CO3+Ca(OH)2 CaCO3+NaCO3+4H2O

heat released 13,700 cal./mole CO2 absorbed– Barium Hydroxide Lime: 20% Barium hydroxide, 80% calcium hydroxide,

and +/- potassium hydroxide,Indicator for color change with exhaustion of CO2 absorption capabilitiesBa(OH)2

. 8H2O+CO2BaCO3+9H2O9H2O+9CO2 9H2CO39H2CO3+9Ca(OH) 2 9CaCO3+18H2O2KOH+H2CO3 K2CO3+2H2OCa(OH)2+K2CO3 CaCO3+2KOH Regeneration (color change loss) with rest can occur. Appears new but is exhausted Granule size 4-8 mesh- 4 mesh equals strainer with 4 openings/inch

Circle system CO2 Absorber System

canisters unlocked

Removing both canisters & soda lime

canister locking lever Removing canister & soda lime

Exhausted soda lime Replacing fresh soda lime

Circle System• Advantages:

– Relative stability of inspired concentration– Conservation of respiratory moisture and heat– Prevention of operating room pollution– PaCO2 depends only on ventilation, not fresh gas

flow– Low fresh gas flows can be used

• Disadvantages:– Complex design = potential for malfunction– High resistance (multiple one-way valves) = higher

work of breathing

Unidirectional or check valve

• Located between vaporizer and common gas outlet reduces the pressure increase due to back pressure caused by IPPV

Circle system Unidirectional Valves• Unidirectional valves-aka flutter valves, one way valves, check valves,

directional valves, dome valves.Found on Inspiratory and Expiratory flow ports

Narkomed MachineOhmeda Machine

Ventilator• Ventilator Components: Driving gas supply, injector, controls, alarms,

safety-release valve, bellows assembly, exhaust valve, spill valve, connection for ventilator hose

Bellows assembly

Ventilator controls

CONTD…………….• Driving gas supply or power gas supply-O2 pneumatically drives (compresses) ventilator bellows

• Injector or Venturi mechanism-Increases the flow of driving gas by using the BERNOULLI Principle- As a gas flow meets a restriction, its lateral pressure drops. Any opening in the tube at this constriction will entrain air (suck air in)

• Controls-Adjusts Flow, Volume, Timing, and Pressure of the driving gas that compresses the bellows

Pneumatic-Uses pressure changes to initiate changes in respiratory cycleFluidic or fluid logic-Uses gas streams through channels in solid material.

Allow forcompact ventilatorElectronic-Electronic control of many addition ventilation parameters powered by a driving gas on newer machines. Must have both power

and pnuematics.• Alarms-ASTM standards group alarms into three levels: High, Medium, Low

Priority correlates to;operator immediate action, prompt action,or awareness. Loss of main power is the only required alarm with a required duration of at least 2 minutes

• Safety relief valve-aka pressure limiting valve, drving gas pressure relief valve. Vents driving gas if factory pre-set pressure is reached (65-80 cm H2O) or adjustable set pressure is reached.

Bernoulli’s Principle

• At constriction:– Flow is higher– Pressure is lower

Ventilator• Bellows Assembly:

Housing- Usually made of hard rigid clear plasticBellows; ASCENDING-standing, upright. Compressed downward during inspiration. ASCEND DURING EXPIRATION

• Pressure is always positive. PEEP 2-4 cm H2O.DESCENDING-hanging, inverted. Compressed upward during inspiration. DESCEND DURING EXPIRATION. Weight of bellows results in negative airway pressure during exhalation until bellow refilled.

• IMPORTANT difference between ascending and descending is that when there is a major leak or disconnect, the ascending bellows will collapse (unless prevented by scavenging system). When a disconnection occurs with a descending bellows system, the ventilator will continue it’s upward movement anddownward movements, drawing in room air and driving gas during it’s

descent and discharging it during the upward movement. Gas flow during upward movement may generate enough pressure such that the low pressure alarm is not activated.

Remember that the type is described by how the bellows move during EXPIRATION

What type is shown?

Scavenger System• Scavenger System consists of: 1) gas collecting assembly, 2) a transfer

means, 3) the interface, 4) gas disposal tubing, 5) gas disposal assembly. (some or all components may be combined).

ASTM standard fitting size for scavenger hoses 19 mm ( international standard 30mm) to prevent incorrect connection to breathing hoses (22mm).

1

32

1

4&5

4&5

Scavenging Systems

• Protects the breathing circuit or ventilator from excessive positive or negative pressure.

Scavenging Systems

Miscellaneous safety mechanisms

• Antistatic wheels and locking of wheels• Backup battery• Pressure relief valve• Common gas outlet with retaining device

to prevent disconnection• Provide temporary electrical power (> 30

min) to monitors and alarms in event of power failure

ESSENTIAL FEATURES PURPOSE

Non-interchangeable gas specific connections to pipeline inlets (DISS) with pressure gauges, filter and check valve

Prevent incorrect pipeline attachments; detect failure, depletion, or fluctuation

Pin Index Safety system for cylinders with pressure gauges, and at least one oxygen cylinder

Prevent incorrect cylinder attachments; provide backup gas supply; detect depletion

Low oxygen pressure alarm Detect oxygen supply failure at the common gas inlet

Minimum oxygen/nitrous oxide ratio controller device (hypoxic guard)

Prevent delivery of less than 21% oxygen

Oxygen failure safety device (shut-off or proportioning device)

Prevent administration of nitrous oxide or other gases when the oxygen supply fails

Oxygen must enter the common manifold downstream to other gases

Prevent hypoxia in event of proximal gas leak

IN A NUTSHELL…

CONTD.Essential features Purpose

Oxygen concentration monitor and alarm Prevent administration of hypoxic gas mixtures in event of a low-pressure system leak; precisely regulate oxygen concentration

Automatically enabled essential alarms and monitors (e.g. oxygen concentration)

Prevent use of the machine without essential monitors

Vaporizer interlock device Prevent simultaneous administration of more than one volatile agent

Capnography and anaesthetic gas measurement

Guide ventilation; prevent anaesthetic overdose; help reduce awareness

Oxygen flush mechanism that does not pass through vaporizers

Rapidly refill or flush the breathing circuit

Danger

Unpleasant Surprises

Checking Anesthesia Machines

8 Categories of check:• Emergency ventilation equipment• High-Pressure system• Low-Pressure system• Scavenging system• Breathing system• Manual and automatic ventilation system• Monitors• Final Position

Anesthesia Machine Checkout

• Steps 1-3:• Emergency Ventilation Equipment

*1. Verify Backup Ventilation Equipment is Available & Functioning

• High Pressure System *2. Check Oxygen Cylinder Supply a. Open 02 cylinder and verify at least half full (about 1000 psi). b. Close cylinder. *3. Check Central Pipeline Supplies a. Check that hoses are connected and pipeline gauges read about 50 psi.

Anesthesia Machine Checkout• Steps 4-7:• Low Pressure Systems

*4. Check Initial Status of Low Pressure System a. Close flow control valves and turn vaporizers off. b. Check fill level and tighten vaporizers' filler caps. *5. Perform Leak Check of Machine Low Pressure System a. Verify that the machine master switch and flow control valves are OFF. b. Attach "Suction Bulb" to common Fresh gas outlet. c. Squeeze bulb repeatedly until fully collapsed. d. Verify bulb stays fully collapsed for at least 10 seconds. e. Open one vaporizer at a time and repeat 'c' and 'd' as above. f. Remove suction bulb, and reconnect fresh gas hose. *6. Turn On Machine Master Switch and all other necessary electrical equipment. *7. Test Flowmeters a. Adjust flow of all gases through their full range, checking for smooth operation of floats and undamaged flowtubes. b. Attempt to create a hypoxic 02/N20 mixture and verify correct changes in flow and/or alarm.

Anesthesia Machine Checkout

• Scavenging System *8. Adjust and Check Scavenging System a. Ensure proper connections between the scavenging system and both APL (pop-off) valve and ventilator relief valve. b. Adjust waste gas vacuum (if possible). c. Fully open APL valve and occlude Y-piece. d. With minimum 02 flow, allow scavenger reservoir bag to collapse completely and verify that absorber pressure gauge reads about zero. e. With the 02 flush activated allow the scavenger reservoir bag to distend fully, and then verify that absorber pressure gauge reads <10 cm H20.

Anesthesia Machine Checkout

• Breathing System *9. Calibrate 02 Monitor a. Ensure monitor reads 21% in room air. b. Verify low 02 alarm is enabled and functioning. c. Reinstall sensor in circuit and flush breathing system with 02. d. Verify that monitor now reads greater than 90%. 10. Check Initial Status of Breathing System a. Set selector switch to "Bag" mode. b. Check that breathing circuit is complete, undamaged and unobstructed. c. Verify that C02 absorbent is adequate. d. Install breathing circuit accessory equipment (e.g. humidifier, PEEP valve) to be used during the case. 11. Perform Leak Check of the Breathing System a. Set all gas flows to zero (or minimum). b. Close APL (pop-off) valve and occlude Y-piece. c. Pressurize breathing system to about 30 cm H20 with 02 flush. d. Ensure that pressure remains fixed for at least 10 seconds. e. Open APL (Pop-off) valve and ensure that pressure decreases.

Anesthesia Machine Checkout

• Manual and Automatic Ventilation Systems 12. Test Ventilation Systems and Unidirectional Valves a. Place a second breathing bag on Y-piece. b. Set appropriate ventilator parameters for next patient. c. Switch to automatic ventilation (Ventilator) mode. d. Fill bellows and breathing bag with 02 flush and then turn ventilator ON. e. Set 02 flow to minimum, other gas flows to zero. f. Verify that during inspiration bellows delivers appropriate tidal volume and that during expiration bellows fills completely. g. Set fresh gas flow to about 5 L/min. h. Verify that the ventilator bellows and simulated lungs fill and empty appropriately without sustained pressure at end expiration. i. Check for proper action of unidirectional valves. j. Exercise breathing circuit accessories to ensure proper function. k. Turn ventilator OFF and switch to manual ventilation (Bag/APL) mode. l. Ventilate manually and assure inflation and deflation of artificial lungs and appropriate feel of system resistance and compliance. m. Remove second breathing bag from Y-piece.

Anesthesia Machine Checkout

• Monitors 13. Check, Calibrate and/or Set Alarm Limits of all Monitors Capnometer, Pulse Oximeter, Oxygen Analyzer, Respiratory Volume Monitor (Spirometer), Pressure Monitor with High and Low Airway Alarms

• Final Position 14. Check Final Status of Machine a. Vaporizers off b. AFL valve open c. Selector switch to "Bag" d. All flowmeters to zero e. Patient suction level adequate f. Breathing system ready to use

THANK U

The essence of intelligence is skill in extracting

meaning from everyday experience