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ANESTHESIA MACHINE. ผศ.พญ.สมัญญา ทิศาวิภาต ภาควิชาวิสัญญีวิทยา คณะแพทยศาสตร์ มหาวิทยาลัยศรีนครินทรวิโรฒ. วัตถุประสงค์. เมื่อจบการบรรยายแล้ว นิสิตสามารถ อธิบายส่วนประกอบและหลักการทำงานของเครื่องดมยาสลบได้อย่างถูกต้อง จำแนกประเภทและเลือกใช้วงจรดมยาสลบได้อย่างเหมาะสม

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Anesthesia machine l.jpgSlide 1


ผศ.พญ.สมัญญา ทิศาวิภาต

ภาควิชาวิสัญญีวิทยา คณะแพทยศาสตร์


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เมื่อจบการบรรยายแล้ว นิสิตสามารถ

  • อธิบายส่วนประกอบและหลักการทำงานของเครื่องดมยาสลบได้อย่างถูกต้อง

  • จำแนกประเภทและเลือกใช้วงจรดมยาสลบได้อย่างเหมาะสม

  • บอกวิธีตรวจสอบเครื่องดมยาสลบและอุปกรณ์ต่างๆ ก่อนการใช้งานตามเกณฑ์มาตรฐานได้

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1. Overview of anesthesia machine

2. Components and systems of anesthesia machine

3. Machine checklist

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Overview of Anesthesia Machine

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Overview of Anesthesia Machine

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A device which delivers a precisely-known but variable gas mixture, including anesthetizing and life sustaining gases.

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Overview of Anesthesia Machine

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Overview of Anesthesia Machine

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Conventional anesthesia machine

Modern anesthesia workstation

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Overview of Anesthesia Machine

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Manufacturing Standards

  • 1988; American Society for Testing and Materials (ASTM) F1161-88

  • 1994; ASTM F 1161-94 (discontinued in 2000)

  • 2000; ASTM F 1850-00

    - Backup for 30 min

    - Monitors: breathing system pressure , exhaled VT ,

    ETCO2, Inhaled anesthetics conc.,

    FiO2, O2 supply pressure,

    SaO2, BP, and ECG.

    - Prioritized alarm system; high, medium, low priority

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1. Overview of anesthesia machine

2. Components and systems of anesthesia machine

3. Machine checklist

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Components and Systems

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Components and Systems

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Medical gas: Types

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Machine gas inlet

  • Most machines have gas inlets for oxygen, nitrous oxide, and air.

  • Separate inlets are provided for the primary pipeline gas supply that passes through the walls of healthcare facilities and the secondary cylinder gas supply.

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Medical Gas: sources

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Pipeline system

  • The centralgas pipeline supply system is the primary source of gas supply for the anesthesia machine.

  • Oxygen is produced by fractional distillation of liquid air and stored as a liquid at -150 to -175oC in a large flask. Safety systems and regulators send oxygen to the hospital pipeline at ~50 psi; the "normal working pressure" of the anesthesia machine.

  • Nitrous oxide is stored as a liquid, at ambient temperature, in large tanks (745 psi- H tank) connected to a manifold which regulates the pipeline pressure to ~50 psi.

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Pipeline system

Central gas pipeline supply system


Multiple gas cylinders

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Pipeline system

Central gas pipeline supply system

Cryogenic tank

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Pipeline system

Connector at user terminal

A. Quick connector (Quick-coupler)

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Pipeline system

Connector at user terminal

B. Diameter Index Safety System (DISS)

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Pipeline system

Machine’s pipeline inlet

Diameter-Index Safety System (DISS)

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Pipeline system

Machine’s pipeline inlet

  • The tubing is color coded and connects to the pipeline inlet of the machine through a noninterchangeablediameter-indexsafetysystem (DISS) fitting that prevents incorrect hose attachment.

  • 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.

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Cylinder supply

The commonly used sizes are;

  • The H Cylinders

    - Sources of gas for small and infrequently used pipeline systems,

    - Intermediate or long-term sources of gas at the patient’s bedside, and

    - Backup source of oxygen, when stored in bulk, in case the pipeline of oxygen fails or is depleted.

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Cylinder supply

The commonly used sizes are;

  • The H Cylinders

    - Sources of gas for small and infrequently used pipeline systems,

    - Intermediate or long-term sources of gas at the patient’s bedside, and

    - Backup source of oxygen, when stored in bulk, in case the pipeline of oxygen fails or is depleted.

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Free-standing H Cylinder

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Cylinder supply

  • The E cylinders

    - Backup sources of gas supply to the anesthesia machine, attached directly to the anesthesia machine via a yoke.

Hanger- yoke assembly

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Cylinder supply

  • The E cylinders

    - Portable oxygen sources

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Cylinder supply

Characteristics of gas cylinders

  • Material: Molybdenumsteel

  • Size: B, D,E, M, G, H or K

    Size E H

    Dimension 4.1/4” x 26” 9.1/4” x 51”

    volume 4.8 L 43.6 L

    Oxygen 1900 psig/660 L 2200 psig/ 6900 L

    Nitrous oxide 745 psig/1590 L 745 psig/15800 L

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Cylinder supply

Characteristics of gas cylinders (cont.)

  • Color coding : Oxygen / Nitrous oxide /Air

  • Components:Cylinder valveis the most fragile part and consists of

    - body

    - port (where the gasexits)

    - stem (shaft)

    - handle or hand wheel (to open the valve)

    - safety relief device

    - conical depression (opposite the port, it accepts the tip of the screw which secures the cylinder in the yoke)

    - PISS pins (Pin Index Safety System)

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Cylinder Valve

A small-cylinder packed valve

A large-cylinder packed valve

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Pin-Index Safety System (PISS)

For small cylinder connection

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Diameter-Index Safety System (DISS)

For large cylinder connection

Nipple and Nut

from Hose

Body at cylinder

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Cylinder supply

Characteristics of gas cylinders (cont.)

  • Cylinder markings: certain codes are stamped near the neck on all medical gas cylinders.

    1.Cylinder specification: DOT, type and material used, service pressure (psi)

    2. Serial number

    3. Commercial designation

    4. Manufacturing data: date of manufacture and original test date, inspector’s official mark, Cylinder qualifies for 110% filling

    5. Manufacturer’s identifying symbol

    6. Retest markings: Data of first 5 year hydrostatic retest, Retester identifying symbol, Cylinder requalifies for 110% filling, Cylinder qualifies for 10-year retest interval.

    7. Neck ring owner’s identification

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Cylinder supply

Cylinder markings

Owner’s Identification

Cylinder specification

Manufacturer’s identifying symbol

Cylinder serial No.

Commercial designation

Retest markings

Manufacturing data

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Cylinder supply

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Cylinder supply

Cylinder safety issues:

  • Standard quality control of cylinder

  • Prevention of wrong gas cylinder connections

  • Securing cylinder against breakage

  • Transfilling

  • Cylinder hazards:

    : improper filling: empty, partially filled, overfilled to near bursting pressures

    : contamination: volatile hydrocarbon

    : unlabeled, painted over (illegible), incorrectly color coded

    : fitted with incorrect valve outlet port, loose/inoperable valve assemblies

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Cylinder supply

Machine cylindrical inlet

  • Cylinders attach to the machine via hanger-yoke assemblies that utilize aPISS to prevent errors.

  • Each yoke assembly includes index pins, a washer, a gas filter, and a check valve that prevents retrograde gas flow.

  • The E cylinders attached to the anesthesia machine are a high-pressure source of medical gases.

  • Cylinder pressure is usually measured by a Bourdon pressure gauge. A flexible tube within this gauge straightens when exposed to gas pressure, causing a gear mechanism to move a needle pointer.

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Electrical power supply

  • Main electrical power is supplied to the machine through a single power cord which can become dislodged.

  • New gas machines must be equipped with battery backup sufficient for 30 minutes of limited operation. What functions remain powered during this period is device-specific.

  • Convenience receptacles are usually found on the back of the machine so that monitors or other equipment can be plugged in. These convenience receptacles are protected by circuit breakers (usually) or fuses.

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Components and Systems

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  • High pressure system

    • Cylinder supply to pressure regulator

  • Intermediate pressure system

    • Pipeline supply to proportioning system

  • Low pressure system

    • Flowmeters to common gas outlet

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PROCESSING: Gas Machine Piping

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Consist of those parts which receive gas at cylinder pressure

Hanger Yoke (Connecting Yoke) for Cylinders

  • PISS

  • Gasket

  • Check valve

    Cylinder pressure gauge

    Cylinder pressure regulators (1st-stage regulators)

    Oxygen: from up to 1900 psig to 45 psig

    Nitrous oxide:from up to 745 psig to 45 psig

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Hanger-yoke assembly

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Double hanger-yoke assembly

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Receive gases at low, relatively constant pressures (37-55 psi)

Pipeline Inlet Connectors

  • DISS

  • Check valve

    Pipeline pressure gauge

    Gas power outlet for anesthesia ventilator

    Anesthesia machine piping system

    Master switch

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Oxygen Fail-Safe Valve (Nitrous Oxide Shutoff Valve)

Oxygen Supply Failure Alarm

Caution : NOT always prevent Hypoxic gas mixture

Oxygen Flush valve

Second stage pressure regulator

Flow control valve

Proportioning system

Link 25 (OhmedaTM) ,

Oxygen Ratio Monitor Control (Draeger)

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Oxygen Fail-safe Valve

  • Pressure sensor

  • shut-off valve

B. Oxygen failure


device (OFPD)

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Flow Control Valve (Needle Valve)

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Proportioning System

Link – 25 system (OhmedaTM)

Oxygen Ratio Monitor Controller (ORMC) (DraegerTM)

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Flow pathway of oxygen

1. Oxygen flush

2. Oxygen supply failure alarm system

3. Pneumatically powered anesthesia ventilator

4. Fail-safe valves

5. Flowmeters

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Include components distal to the flow meter needle valves

Flow meter tubes

  • Thorpe tube

  • indicator


    Check valve

    Common gas outlet

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Flow meter tubes

Thorpe tube


bobbin ball

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Flow meter tubes

Sequence of flow meter tubes



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-Produce a controlled and predictable concentration of anesthetic vapor in the carrier gas passing through the vaporizing chamber.

Operating principle: Variable bypass vaporizers

- Total FGF enters and splits into carrier gas and bypass gas, then join at the vaporizer outlet.

- Splitting ratio is controlled by

..concentration control dial, and

..automatic temperature compensation


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Factors affecting vaporizer output:

1. FGF (fresh gas flow) rate

-constant output over FGF rate of 250 ml/min to 15 L/min

2. Ambient temperature

-linear output from 20 – 35 degrees C

3. Intermittent back pressure causing pumping effect

-prevention by check valve

smaller vaporizing chamber

tortuous inlet chambers

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Safety features of anesthesia voporizer:

  • Agent specific and concentration-calibrated

  • Vaporizerinterlocks

  • Liquid level indicated, designed to prevent overfilling

  • Keyed fillers

  • No discharge of liquid anesthetic occurs from the vaporizer even at maximum fresh gas flow

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Keyed fillers

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Components and Systems

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  • Anesthetic gas exits the anesthesia machine via the common gas outletand enters a breathing circuit.

  • The function of the circuit is to deliver oxygen and anesthetic gases to the patient and to eliminate carbon dioxide.

  • The carbon dioxide may be eliminated by gas inflow or bysodalime absorption.

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Circle absorption System

The Circlesystem can be either

  • closed(fresh gas inflow exactly equal to patient uptake, complete rebreathing after carbon dioxide absorbed, and pop-off closed)

  • semi-closed (somerebreathingoccurs, FGFandpop-offsettingsatintermediatevalues), or

  • semi-open(no rebreathing, high fresh gas flow [higher than minute ventilation])

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Circle absorption System

  • Advantages

    • low FGF required, low pollution & cost from gases & inhalation agents

    • PaCO2 depends on ventilation only

    • keep heat and moisture

  • Disadvantages

    • complex, difficult to disinfections

    • high resistance due to unidirectional valve

    • more possibility of leakage or disconnections in circuit

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Circle absorption System -components

  • fresh gas inflow site

  • inspiratory & expiratory unidirectional valves

  • inspiratory & expiratory corrugated tubing

  • Y connector

  • Pop-off, adjustable pressure-limiting valve, or APL valve)

  • Carbon dioxide canisters and absorbents

  • Reservoir bag

  • Bag/ventilator selector switch

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Circle absorption System

Flow of anesthetic gas through circle breathing system

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Circle absorption System

  • Carbon dioxide absorbents

  • Function:

  • conserving gases and volatile agents

  • decreasing OR pollution

  • avoiding hazards of carbon dioxide rebreathing.

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Circle absorption System

Carbon dioxide absorbents

Type: Soda lime

  • Activator is NaOH or KOH. Silica and kieselguhr added as hardeners.

  • Indicators for SodasorbTM (such as ethyl violet) are colorless when fresh, and purple when exhausted, because of pH changes in the granules.

CO2 + H2O --> H2CO3

H2CO3 + 2 NaOH (or KOH) --> Na2CO3 (or K2CO3) + 2 H2O + Energy

Na2CO3 (or K2CO3) + Ca(OH)2 --> CaCO3 + 2 NaOH (or KOH)

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Circle absorption System

Carbon dioxide absorbents

Type: Baralyme

  • Activator Ba(OH)2, octahydrate; no hardeners, slightly less efficient.

  • Colorless or pink changing to blue-gray with exhaustion.

Ba(OH)2-8 H2O + CO2 --> BaCO3 + 9 H2O + Energy

9 H2O + 9 CO2 --> 9 H2CO3 (Then by direct reactions and by NaOH, KOH if present)

9 H2CO3 + 9 Ca(OH)2 --> CaCO3 + 18 H2O + Energy

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Circle absorption System

  • Advantages

    • low FGF required, low pollution & cost from gases & inhalation agents

    • PaCO2 depends on ventilation only

    • keep heat and moisture

  • Disadvantages

    • complex, difficult to disinfections

    • high resistance due to unidirectional valve

    • more possibility of leakage or disconnections in circuit

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Non-rebreathing Systems

Mapleson breathing system A - F

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Non-rebreathing Systems

  • Advantages

    • Simply, light weight, easy to positioning

    • Remote anesthesia

    • Low resistance

  • Disadvantages

    • Require high FGF, more pollution

    • loss more heat and water from airway

    • Carbon dioxide retention

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Modified Mapleson breathing system

  • Ayre’s T-piece circuit (Mapleson E)

    • most suitable in oxygen therapy

    • caution : require high flow of humidified oxygen

  • Jackson Rees circuit (Mapleson F)

    • most suitable in pediatric anesthesia (BW < 20 kg.)

    • require high flow 2-3 times of minute ventilation

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Components and Systems

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  • The collection and removal of vented anesthetic gases from the OR.

    Scavenger and operating room ventilation efficiency are the two most important factors in reduction of waste anesthetic gases (WAGs).

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  • Active

    • Suction applied

    • Require a means to protect patient’s airway from suction or build up of positive pressure

  • Passive

    • waste gases proceed passively down corrugated tubing through the exhaust grill of the OR.

    • Require a means to protect patient’s airway from build up of positive pressure only.

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Scavenging interface

  • The most important component.

  • Protects breathing system from excess positive or negative pressure.

  • Reservoir is highly desirable with active system.

  • Closed interface communicates with atmosphere only through valves.

Closed scavenging interface

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Closed scavenging interface

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1. Overview of anesthesia machine

2. Components and systems of anesthesia machine

3. Machine checklist

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Machine Checklist

  • Pre-anesthesia checklist 2008

  • Electronic and automated checklist

  • Local department checklist procedures

  • Minimum test under life-threatening conditions

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WHY negative pressure leak test?

A high pressure check of the breathing circuit will not detect leaks upstream of check valves, since the high pressure in the breathing circuit will only be transmitted upstream to the check valve, and no further.

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Negative pressure leak test

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Negative pressure leak test

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Future Anesthesia Machine

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Questions from audience

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