Inhaled anesthetic Delivery Inhaled anesthetic Delivery SystemsSystems

Sahmeddini MDDepartment of Anesthesia Shiraz medical university

Inhaled anesthetic Delivery Inhaled anesthetic Delivery SystemsSystems

Safety StandardsSafety Standards

ANSI - (American National Standards ANSI - (American National Standards Institute)Institute)

19791979 -- -- Standards set for all machines sold in Standards set for all machines sold in the U.Sthe U.S..

ASTM -- (American Society for Testing and ASTM -- (American Society for Testing and Materials 1988Materials 1988

19941994 : :ASTM F1161-94ASTM F1161-9420002000 : :ASTM F1850-00ASTM F1850-00

To comply with the 2000 ASTM F1850-00 standardTo comply with the 2000 ASTM F1850-00 standard

Continuous breathing system pressureContinuous breathing system pressureExhaled tidal volumeExhaled tidal volumeVentilatory carbon dioxide concentrationVentilatory carbon dioxide concentrationAnesthetic vapor concentrationAnesthetic vapor concentrationInspired oxygen concentrationInspired oxygen concentration Oxygen supply pressureOxygen supply pressure Arterial oxygen saturation of hemoglobinArterial oxygen saturation of hemoglobinArterial blood pressureArterial blood pressure Continuous electrocardiogramContinuous electrocardiogram . .

Functions of anesthesia machineFunctions of anesthesia machine

Convert supply gases from high pressure to Convert supply gases from high pressure to low pressurelow pressure

Convert liquid agent to gasConvert liquid agent to gasDeliver in a controlled mannerDeliver in a controlled manner Provide positive pressure for ventilationProvide positive pressure for ventilationAlert the provider to malfunctionAlert the provider to malfunction Prevent delivery of a hypoxic mixturePrevent delivery of a hypoxic mixture

Testing Specific Components of the Testing Specific Components of the Anesthesia Delivery SystemAnesthesia Delivery System

11))Calibration of the oxygen analyzerCalibration of the oxygen analyzer

22 ) )The low-pressure circuit leak testThe low-pressure circuit leak test

33 ) )The circle system testsThe circle system tests..

High Pressure SystemHigh Pressure System

Receives gasses from the high pressure E Receives gasses from the high pressure E cylinders attached to the back of the cylinders attached to the back of the

anesthesia machineanesthesia machine . .((22002200 psig for O2, 745psig for N2Opsig for O2, 745psig for N2O)

High Pressure System

Receives gasses from the high Receives gasses from the high pressure E cylinders attached pressure E cylinders attached to the back of the anesthesia to the back of the anesthesia

machinemachine 22002200 psig for O2psig for O2 745745 psig for N2Opsig for N2OUsually not used, unless Usually not used, unless

pipeline gas supply is offpipeline gas supply is off

High Pressure SystemHigh Pressure System

Hanger YokeHanger YokeHanger Yoke: orients Hanger Yoke: orients

and supports the and supports the cylindercylinder

Providing a gas-tight Providing a gas-tight sealseal

Ensuring a Ensuring a unidirectional gas flow unidirectional gas flow

into the machineinto the machine

Pin Index Safety System(PISS)

Prevents tank swapsPin positionsAir 1-5Oxygen 2-5Nitrous oxide 3-5

Pin Index Safety System(PISS)Pin Index Safety System(PISS)

•Pipeline 50 psig•Tanks•»Oxygen: 2200 psig• »Nitrous oxide: 745 psig• »Both reduced to 45 psig upon entering the

machine

Two sources of gas:

Tank

H TankH Tank

E TankE Tank

E Size Compressed Gas CylindersE Size Compressed Gas CylindersCylinder Characteristics Oxygen Nitrous Oxide Air

ColourColour WhiteWhite BlueBlue BlackBlack

StateState GasGas Liquid and gasLiquid and gas GasGas

Contents (L)Contents (L) 625625 15901590 625625

Empty WeightEmpty Weight((kgkg))

5.905.90 5.905.90 5.905.90

Full Weight (kg)Full Weight (kg) 6.766.76 8.808.80 6.506.50

Pressure FullPressure Full((psigpsig))

20002000 750750 18001800

Oxygen cylinder pressure(psig)Oxygen cylinder pressure(psig) 200200. . oxygen flow rate(L/minoxygen flow rate(L/min)

Approximate remaining time#Approximate remaining time#

Intermediate Pressure System

Intermediate Pressure SystemIntermediate Pressure System

Receives gassesReceives gasses from the regulatorfrom the regulator

or the hospitalor the hospitalpipeline at pressures of pipeline at pressures of

40-55 psig40-55 psig

Pipeline Inlet ConnectionsPipeline Inlet Connections

•Mandatory N2O and O2,usually have air and suction too

•Inlets are non interchangeable due to specific threading as per the Diameter Index

Safety System (DISS)

Diameter Index Safety System (DISS)Diameter Index Safety System (DISS)

Oxygen Pressure Failure Devices

Machine standard requires that an Machine standard requires that an anesthesia machine be designed so that anesthesia machine be designed so that whenever the oxygen supply pressure is whenever the oxygen supply pressure is

reduced below normal, the oxygen reduced below normal, the oxygen concentration at the common gas outlet does concentration at the common gas outlet does

not fall below 19%not fall below 19%

Oxygen Pressure Failure Devices

A Fail-Safe valve is present in the gas line supplying each of the flow meters except O2 .

This valve is controlled by the O2 supply pressure and This valve is controlled by the O2 supply pressure and shuts off or proportionately shuts off or proportionately decreases the supply decreases the supply

pressure of all other gasses as the O2 supply pressure of all other gasses as the O2 supply pressure decreasespressure decreases

Oxygen Pressure Failure Devices

Historically there are 2 kinds of fail-safe valvesHistorically there are 2 kinds of fail-safe valves

Pressure sensor shut-off valve (Ohmeda)Pressure sensor shut-off valve (Ohmeda)

Oxygen failure protection device (DragerOxygen failure protection device (Drager)

Pressure Sensor Shut-Off ValvePressure Sensor Shut-Off Valve

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

If the oxygen supply pressure falls belowIf the oxygen supply pressure falls below the threshold value the valve closes and thethe threshold value the valve closes and the gas in that limb (e.g..N2O), does not advance to its gas in that limb (e.g..N2O), does not advance to its

flow controlflow control

Pressure sensor shut-off valvePressure sensor shut-off valve

Oxygen Failure Protection Device Oxygen Failure Protection Device (OFPD(OFPD)

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

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

Oxygen failure protection deviceOxygen failure protection device

Oxygen Supply Failure AlarmOxygen Supply Failure Alarm

The machine standard specifies that whenever The machine standard specifies that whenever the oxygen supply pressure falls below a the oxygen supply pressure falls below a

manufacturer specified threshold manufacturer specified threshold (usually 30 (usually 30 psig) psig) alarm shall blow within 5 secondsalarm shall blow within 5 seconds.

Limitations of Fail-Safe Devices/AlarmsLimitations of Fail-Safe Devices/Alarms

Fail-safe valves do not prevent administration Fail-safe valves do not prevent administration of a hypoxic mixture because they depend on of a hypoxic mixture because they depend on

pressure and not flowpressure and not flow..

Do not prevent hypoxia from accidents such as Do not prevent hypoxia from accidents such as pipeline crossovers or a cylinder containing the pipeline crossovers or a cylinder containing the

wrong gaswrong gas..

OXYGEN FLUSH VALVEOXYGEN FLUSH VALVEBy passes vaporizerBy passes vaporizerDelivers large volumes Delivers large volumes

of oxygen to breathing of oxygen to breathing circuitcircuit

Is under high(er) Is under high(er) pressure cautionpressure caution!!!!!!

OXYGEN FLUSH VALVEOXYGEN FLUSH VALVEReceives 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/minThe ability to provide jet ventilation Hazards:May cause barotraumasDilution of inhaled anesthetic

Second-Stage ReducingDevice

Located just upstream of the flow control valves

Receives gas from the pipeline inlet or the cylinder reducing device and reduces it further

to26 psig for N2O and14 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 tothe common gas outlet Consists of: Flow metersFlow metersVaporizer mounting deviceVaporizer mounting deviceCheck valveCheck valveCommon gas outletCommon gas outlet

Flow Meter AssemblyFlow Meter 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

Flow Meter Flow Meter

Flow Meter StandardsFlow Meter Standards

Oxygen flow control knob Physically differentOxygen flow control knob Physically differentLarger and projects furtherLarger and projects furtherDifferent shapeDifferent shape All knobs are colour codedAll knobs are colour coded Knobs are protectedKnobs are protected

•Some newer anaesthesia workstations have now replaced the conventional glass flow tubes with

electronic flow sensors that measure the flow of the individual gases .

•These flow rate data are then presented to the anaesthesia care provider in either numerical format,

graphic format, or a combination of the two.

Electronic flow sensors

Cracked tubesCracked tubes

In the presence of a flow meter leak (either

at the “O” ring or the glass of the flow tube)

a hypoxic mixture is less likely to occur if the O2

flow meter is downstream of all other

flow meters

Proportioning Systems

•Mechanical integration of the

•N2O and O2 flow control valves

•Maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1

Proportioning Systems

Proportioning Systems

Proportioning Systems

VaporizersVaporizers

•A vaporizer is an instrument designed to change a liquid anesthetic agent into its vapor

and add a controlled amount of this vapor to the fresh gas flow

VaporizersVaporizers

Classification of VaporizersClassification of Vaporizers

Methods of regulating output concentrationConcentration calibrated Method of vaporizationFlow-overBubble throughInjectionTemperature compensation:ThermocompensationSupplied heat

Applied PhysicsApplied Physics

•Vapor pressure•Based on characteristics of agent•Varies with temperature•Boiling point: Vapor pressure equals atmospheric

pressure•Latent heat of vaporization: Heat required to

change liquid into a vapor•Comes from liquid •environment

Ohmeda and Drager CharacteristicsOhmeda and Drager Characteristics

•Variable bypass• Flow over• Temperature compensated•Agent specific•Out of circuit

Basic Design

•Gas enters vaporizer•Flow is split•Majority is by passed•Some enters vaporizing chamber•Saturated gas leaves chamber•Diluted by bypass gas•Delivered to patient

Generic Bypass VaporizerGeneric Bypass Vaporizer

•Flow from the flow meters enters the inlet of the vaporizer

•The function of the concentration control valve is to regulate the amount of flow

through the bypass and vaporizing chambers•Splitting Ratio = flow though vaporizing

chamber/flow through bypass chamber

Factors that Effect OutputFactors that Effect Output

Flow rateFlow rateAccurate at most flowsAccurate at most flowsLower than dial setting at both extremes of Lower than dial setting at both extremes of

flowflowTemperatureTemperatureVapor pressure varies with tempVapor pressure varies with tempAccurate at 20 - 35 CAccurate at 20 - 35 C

Factors that Effect OutputFactors that Effect Output

•Intermittent back pressure•Retrograde flow•Higher than dial setting•especially at low flows and high•ventilator pressures•Carrier gas composition•N2O causes transient drop

Carbon Dioxide Absorbents

•Two formulations of carbon dioxide absorbents are Two formulations of carbon dioxide absorbents are commonly available todaycommonly available today::

•soda limesoda lime • calcium hydroxide limecalcium hydroxide lime•Baralyme, or barium hydroxide limeBaralyme, or barium hydroxide lime

CO2 Absorption (con’t)

•Soda lime•–94% calcium hydroxide•–5% sodium hydroxide•–1% potassium hydroxide•–silica to harden granules•–ethyl violet as an indicator

CO2 Absorption (con’t)

•Ethyl violet is the pH indicator added to both soda Ethyl violet is the pH indicator added to both soda limelime

•Ethyl violet changes from colorless to violet when the Ethyl violet changes from colorless to violet when the pH of the absorbent decreases as a result of carbon pH of the absorbent decreases as a result of carbon

dioxide absorptiondioxide absorption.

•Unfortunately, in some circumstances ethyl violet Unfortunately, in some circumstances ethyl violet may not always be a reliable indicator of the may not always be a reliable indicator of the

functional status of absorbentfunctional status of absorbent

Anesthesia Ventilators

•The ventilator on the modern anesthesia workstation The ventilator on the modern anesthesia workstation serves as a mechanized substitute for the hand of the serves as a mechanized substitute for the hand of the

anesthesia care provider in manipulating the anesthesia care provider in manipulating the reservoir bag of the circle system, or another reservoir bag of the circle system, or another

breathing systembreathing system..

Ventilators Classified by:•Power source

–pneumatic–electric –both•Drive mechanism

–double circuit–driven by oxygen

Ventilator Problems (con’t)

•Leak in bellows assembly

•Mechanical problems

•Electrical problems

Setting the Ventilator

Based on the principle that PaCO2 is directly proportional

to alveolar ventilation

AV X CO2 = AV X CO2

(what you have) (what you want)

AV = alveolar ventilationCO2 = carbon dioxide

If you know 3, you can solve for the 4th

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

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

followedfollowed::–Unidirectional valves Unidirectional valves

between the patient and the between the patient and the reservoir bagreservoir bag

–Fresh-gas-flow cannot enter Fresh-gas-flow cannot enter the circuit between the the circuit between the

expiratory valve and the expiratory valve and the patientpatient

–Adjustable pressure-limiting Adjustable pressure-limiting valve (APL) valve (APL) cannot be cannot be

located between the patient located between the patient and the inspiratory valveand the inspiratory valve

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

The Adjustable Pressure Limiting (APL) Valve

•User adjustable valve that releases gases to the scavenging system and is

intended to provide control of the pressure in the breathing system

•Bag-mask Ventilation: Valve is usually left partially open. During inspiration the bag is squeezed pushing gas into

the inspiratory limb until the pressure relief is reached, opening the APL valve .

•Mechanical Ventilation: The APL valve is excluded from the circuit when the

selector switch is changed from manual to automatic ventilation

The Adjustable Pressure Limiting (APL) Valve

Scavenging Systems

•Scavenging is the collection and removal of vented anesthetic gases from the OR

•Since the amount of anesthetic gas supplied usually far exceeds the amount necessary for

the patient, OR pollution is decreased by scavenging

Scavenging Systems

Workers should not be exposed to an eight hour Workers should not be exposed to an eight hour time-weighted average of > 2 ppm time-weighted average of > 2 ppm

halogenated agents (not > 0.5 ppm if nitrous halogenated agents (not > 0.5 ppm if nitrous oxide is in use) or > 25 ppm nitrous oxideoxide is in use) or > 25 ppm nitrous oxide.

Evidence of harm to anesthesia personnel from waste gases is

suggestive but unproved (strongest relationship is N2O and reproductive difficulties).

Type of Scavenging Systems

•Scavenging may be active (suction applied)

•passive (waste gases proceed passively down corrugated tubing through the room

ventilation exhaust grill of the OR) .

Hazards of scavenging

•Obstruction distal to interfaceObstruction distal to interface

•Occupational exposureOccupational exposure

•Barotrauma or inability to ventilateBarotrauma or inability to ventilate

High-Pressure System Checkout    Check Oxygen Cylinder SupplyCheck Oxygen Cylinder Supply    .    .      Open the OOpen the O22 cylinder and verify that it is at cylinder and verify that it is at

least half full (≈1000 psi)least half full (≈1000 psi)            Close the cylinderClose the cylinder..Check Central Pipeline SuppliesCheck Central Pipeline Supplies    .    .      Check that hoses are connected and pipeline Check that hoses are connected and pipeline

gauges read about 50 psigauges read about 50 psi..

System Checkout

Low-Pressure System

Check Initial Status of Low-Pressure SystemCheck Initial Status of Low-Pressure System   .   .a. Close the flow control valves and turn the a. Close the flow control valves and turn the

vaporizers offvaporizers off    .    .b. Check the fill level and tighten the b. Check the fill level and tighten the

vaporizers’ filler capsvaporizers’ filler caps..

Perform Leak Check of Machine Low-Pressure System.

Verify that the machine master switch and flow Verify that the machine master switch and flow control valves are OFFcontrol valves are OFF    

Attach a “suction bulb” to the common (fresh) Attach a “suction bulb” to the common (fresh) gas outletgas outlet        

Squeeze the bulb repeatedly until it is fully Squeeze the bulb repeatedly until it is fully collapsedcollapsed      .      .

Verify that the bulb stays fully collapsed for at Verify that the bulb stays fully collapsed for at least 10 secondsleast 10 seconds        .        .

Open one vaporizer at a time and repeat steps c Open one vaporizer at a time and repeat steps c and d as aboveand d as above        .        .

Remove the suction bulb and reconnect the fresh Remove the suction bulb and reconnect the fresh gas hosegas hose..

Turn on Machine Master Switch and All Other Turn on Machine Master Switch and All Other Necessary Electrical EquipmentNecessary Electrical Equipment.

Test Flow MetersTest Flow Meters..   a.a. Adjust the flow of all gases through their Adjust the flow of all gases through their

full range while checking for smooth operation full range while checking for smooth operation of the floats and undamaged flow tubesof the floats and undamaged flow tubes    .    .

b. b. Attempt to create a hypoxic O Attempt to create a hypoxic O22/N/N22O O mixture and verify correct changes in flow mixture and verify correct changes in flow

and/or alarmand/or alarm..

Calibrate O2 Monitor

a.a. Ensure that the monitor reads 21% in Ensure that the monitor reads 21% in room airroom air   .   .

b. b. Verify that the low-O Verify that the low-O22 alarm is enabled alarm is enabled and functioningand functioning    .    .

c. c. Reinstall the sensor in the circuit and flush Reinstall the sensor in the circuit and flush the breathing system with Othe breathing system with O22    .    .

d. d. Verify that the monitor now reads greater Verify that the monitor now reads greater than 90%than 90%..

Check Initial Status of Breathing System.

a. a. Set the selector switch to “Bag” mode Set the selector switch to “Bag” mode   .   . b.b. Check that the breathing circuit is Check that the breathing circuit is

complete, undamaged, and unobstructedcomplete, undamaged, and unobstructed    .    .c. c. Verify that CO Verify that CO22 absorbent is adequate absorbent is adequate    .    .d. d. Install the breathing circuit accessory Install the breathing circuit accessory

equipment (e.g., humidifier, positive end-equipment (e.g., humidifier, positive end-expiratory pressure [PEEP] valve) to be used expiratory pressure [PEEP] valve) to be used

during the procedureduring the procedure..

Perform Leak Check of Breathing System.

Set all gas flows to zero (or minimum)Set all gas flows to zero (or minimum)      .      .Close the APL (pop-off) valve and occlude the Close the APL (pop-off) valve and occlude the

Y-pieceY-piece      .      .Pressurize the breathing system to about Pressurize the breathing system to about

30 cm H30 cm H22O with an OO with an O22 flush flush      .      .Ensure that the pressure remains fixed for at Ensure that the pressure remains fixed for at

least 10 secondsleast 10 seconds        .        .Open the APL (pop-off) valve and ensure that Open the APL (pop-off) valve and ensure that

the pressure decreasesthe pressure decreases