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Anaesthesiology
The Anesthesia Workstation and Delivery Systems for Inhaled Anesthetics
Built from Barash Clinical Anesthesia, 9th Edition
What’s inside
14 sections · 196 slides
Overview
- Scope of this topic
- Importance of the gas delivery system
Anatomy of the Delivery System
- Basic configuration of the delivery system
- The five stages of gas delivery
- Function of the machine and the vaporizer
- Function of the patient breathing circuit
- Waste gas scavenging and the term workstation
- Generic two-gas anesthesia machine
- Three pressure circuits of the machine
- Pressures in the high- and intermediate-pressure circuits
- Contents of the low-pressure circuit
- Two supply sources for every gas
- Flow control valves and the path to the outlet
- The outlet check valve and the oxygen flush connection
Pipeline and Cylinder Supply
- The hospital central piping system
- Reported pipeline failures and crossover deaths
- Management of a suspected pipeline crossover
- Reason the pipeline must be disconnected
- Gas-specific wall outlet connections
- Wall outlets and DISS connections
- Machine gas inlet and cylinder pin connections
- Backup cylinders and the hanger yoke
- The Pin Index Safety System and its limits
- E-cylinder valve and yoke components
- Cylinder check valves and pressure gauge
- Cylinder pressure regulator and the transport valve
- Rationale for keeping cylinder valves closed
- Cylinder DISS outlet as an oxygen backup
- Boyle's law and the volume in a full E-cylinder
- Estimating remaining oxygen supply time
- Physical properties of nitrous oxide
- Contents of a nitrous oxide E-cylinder
- Reading the nitrous oxide cylinder gauge
- Nitrous oxide supply into the machine
- Oxygen paths within the intermediate-pressure system
Oxygen Supply Pressure Failure Devices
- Cascade of protective devices and the pressure alarms
- The oxygen failure cutoff valve
- Pressure-sensor shutoff valve in the open and closed positions
- Threshold valves and the second-stage oxygen regulator
- Failure of the fail-safe valve to prevent a hypoxic mixture
- Five ways a hypoxic mixture can still be delivered
Flowmeters and Gas Flow Control
- Oxygen flowmeter assembly
- Thorpe tubes and electronic flow sensors
- Electronic presentation of the flow rate
- The annular space
- Constant-pressure variable-orifice flowmeters
- Flow tube constriction and the physics of gas flow
- Flow control knob safety and the flowmeter scale
- Electronic control panel with soft keys
- Flow tubes, indicator floats and float stops
- Flowmeter leaks and causes of inaccuracy
- Flowmeter sequence as a cause of hypoxia
- Oxygen flow tube leak
- Electronic flow display and fresh gas flow optimization
- Total flow indicator that survives a power failure
- The GE Aisys Carestation gas mixer
- Alternate oxygen flowmeter backup system
- Low-flow wizard recommendations
- How the Low Flow Wizard calculates, and its limits
- The GE ecoFLOW tool
Proportioning Systems
- Purpose of nitrous oxide/oxygen proportioning systems
- Ohmeda Link-25 Proportion-Limiting Control System
- Mechanics and pneumatics of the Link-25 system
- How the Link-25 corrects an unsafe setting
- Draeger Sensitive Oxygen Ratio Controller
- Components and operating principle of the S-ORC
- Behaviour of the S-ORC shaft
- Link-25 compared with the S-ORC
- Wrong supply gas defeats both systems
- Defective mechanics and leaks downstream
- Oxygen dilution by inert gases and volatile agents
- The oxygen flush valve
Vaporizer Physics
- Evolution and classification of vaporizers
- Physical properties of potent inhaled volatile anesthetic agents
- Saturated vapor pressure
- Saturated vapor pressure versus temperature curves
- Boiling point and latent heat of vaporization
- Specific heat and thermal conductivity
- Physical properties that shape vaporizer design
Variable Bypass Vaporizers
- Meaning of each classification term
- Generic variable bypass vaporizer
- Principle of dilution in a variable bypass vaporizer
- Path of gas through the vaporizer
- Filling the sump and estimating agent consumption
- Worked example: 1% sevoflurane
- Worked examples: 2% sevoflurane and isoflurane
- Bimetallic strip temperature compensation
- Expansion element temperature compensation
- Ideal vaporizer performance and the effect of fresh gas flow
- Temperature compensation and vaporizer safety features
- The pumping effect
- Proposed mechanism of the pumping effect
- Limiting the pumping effect, and carrier gas solubility
- Influence of carrier gas composition on delivered concentration
- Misfilling and deliberate agent-vaporizer mismatch
- Predicting the output of a misfilled vaporizer
- Tipping of a vaporizer
- Management after tipping, and improper filling
- Tipping-resistant designs and use in the MRI suite
- Vaporizer leaks and leak testing
Vaporizers for Desflurane
- Physical properties that force a new design
- Unsuitability of variable bypass vaporizers for desflurane
- Tec 6 desflurane vaporizer schematic
- Heated sump, shutoff valve and pressure regulator
- How the two circuits are matched
- Working pressure of the Tec 6
- Fresh gas flow rate versus working pressure
- Fresh Gas Flow Rate versus Working Pressure
- Constant fresh gas flow with a rising dial setting
- Dial Setting versus Flow through Restrictor R2
- Constant dial setting with a rising fresh gas flow
- Effect of altitude on older Tec type vaporizers
- Performance of older Tec type vaporizers versus the Tec 6 at varying ambient pressures
- Partial pressure and ambient pressure compensation
- Tec type versus Tec 6 output across ambient pressures
- Altitude correction and carrier gas effects on the Tec 6
- Desflurane misfilling hazard and the Saf-T-Fill adapter
- Misfilling a Tec 6 and what triggers its shutoff valve
- Desflurane vaporizer alarm indicators
- Meaning of the D-Vapor alarms
Aladin Cassette and Injection Vaporizers
- Aladin cassette concept and injection vaporizers
- Aladin sevoflurane cassette
- Aladin cassettes mounted on a GE Aisys Carestation
- Aladin cassette vaporizer schematic
- Inputs to the Aladin central processing unit
- Aladin check valve and agent heating
- Aladin behaviour above the boiling point of desflurane
- Comparison of vaporizer types
- Vaporizer Models and Characteristics
The Circle Breathing System
- Function of the breathing circuit and recent design changes
- Components of the circle breathing system
- Seven primary components of the circle system
- Universal F circuit and the three anti-rebreathing rules
- Semiopen, semiclosed and closed circle systems
- Efficiency and advantages of the circle system
- Hazards of circle system complexity and obstruction
- Malfunction of the unidirectional valves
- Flow transducer leaks and kinked tubing
- Coaxial versus dual-limb breathing tubes
- Effect of longer breathing circuit tubing
Carbon Dioxide Absorbents
- Absorbent safety concerns and the ideal absorbent
- Canister leaks and the cost of calcium hydroxide lime
- Composition of high-moisture soda lime
- Calcium hydroxide lime
- Granule size and absorptive capacity
- The chemistry of carbon dioxide absorption
- Sequence of the absorption reaction
- Ethyl violet as a pH indicator
- Failure of the colour indicator
- Compound A: formation and the factors that raise it
- Effect of absorbent dehydration on compound A
- Carbon monoxide production from desiccated absorbents
- The Monday morning pattern of carbon monoxide poisoning
- Retrograde drying and low-strong-base products
- Factors that increase carbon monoxide production
- Interventions to reduce carbon monoxide exposure
- APSF 2005 recommendations on absorbent safety
- Breathing system fires and lithium-based absorbents
- Ingredients of a breathing system fire
- Litholyme indicator and SpiraLith Ca
- Absorbent comparisons
Mapleson Circuits and the Resuscitation Bag
- Origin and components of the Mapleson systems
- Mapleson breathing systems
- Functional groups within the Mapleson family
- Flow requirement of the Mapleson A circuit
- Rebreathing variables and flow needs of the Mapleson systems
- Structure of the Bain circuit
- Advantages and hazards of the Bain circuit
- The Pethick test of inner tube integrity
- The Jackson-Rees circuit
- The self-inflating resuscitation bag as plan B
Summary and Key Points
- Key point: limits of the oxygen failure cutoff valves
- Key point: two actions in a pipeline crossover
- Key point: why desflurane needs a special vaporizer
- Key point: absorbent interactions with inhaled anesthetics
- Key point: the low-pressure circuit as the vulnerable area
- Key point: which leak test to use
- Summary: the journey of one breath
- Summary: the recurring safety themes
- Sources cited in this topic
- Sources cited in this topic (continued)
- Sources cited in this topic (continued)
- Barash, Cullen, and Stoelting's Clinical Anesthesia, 9th Edition