Vaporizers Flashcards
What is the function of a vaporizer?
Change liquid anesthetic into vapor, adds controlled amt of vapor to FGF/BS
What is a vapor?
volatile liquid in closed container, molecules enter space above it
Dynamic equilibrium forms if container kept at constant temperature
What is saturated vapor pressure?
highest partial pressure vapor can achieve at certain temperature
At constant temp, dynamic equilibrium reached btw liquid, vapor
What is the proportional effect of temperature on vapor pressure?
Increased temp = increased VP, more molecules added to vapor phase
decreased temp = decreased VP
What is VP affected by?
Liquid, Temp
IS NOT AFFECTED BY AMBIENT PRESSURE
Halothane SVP (torr, 20*C)
243mm Hg
Enflurane SVP (torr, 20*C)
172mm Hg
Isoflurane SVP (torr, 20*C)
240mm Hg
Desflurane SVP (torr, 20*C)
700 mm Hg
Sevoflurane SVP (torr, 20*C)
160mm Hg
Boiling Point
Where vapor pressure = atmospheric pressure
BP decreases with lower atmospheric pressure (?)
Agents with lower BPs: more susceptible to changes in Patm
BP (*C) Halothane at 760mm Hg
50.2
BP (*C) Enflurane at 760mm Hg
56.5
BP (*C) Isoflurane at 760mm Hg
48.5
BP (*C) Desflurane at 760mm Hg
22.8
BP (*C) Sevoflurane at 760mm Hg
59
Partial Pressure
part of total pressure in container DT one gas in mixture of gases
Dalton’s Law: partial pressure exerted by gas
Depends only on temperature, NOT total pressure above liquid
Absolute value
How is partial pressure related to patient depth?
Directly
What is vapor pressure?
Highest partial pressure that can be exerted by a gas at a given temperature
Volumes percent
Number of units of vol of gas IRT total of 100 units of vol for total liquid
Percentage of vol (V/V%) of gas = (Partial pressure of gas/total pressure of air)*100
Vol % = relative ratio
How is vol percent related to patient depth?
Indirectly
Heat of Vaporization
Energy needed for molecules in liquid phase to move into gas phase
Number of calories needed to convert 1g of liquid into vapor
What happens as vaporization proceeds?
As vaporization proceeds, liquid temp drops
Gradient forms, heat flows from surroundings to liquid to equilibrate temperature
Lower liquid temperature, greater the gradient, greater flow of heat from surroundings
Specific Heat
Quantity of heat required to raise temp of 1g of substance by 1*C
Higher specific heat, more heat required to raise temperature of given quantity of that substance
Alternative definition: amt of heat required to raise temp of 1mL of substance by 1C, standard = H2O at 1cal/g/C (1cal/mL/*C)
Why is specific heat important to anesthesia vaporizers?
How much heat must be supplied to liquid ax to maintain stable temp during vaporization?
Choosing material for vaporizer: materials with high specific heat experience more gradual temperature changes
Thermal Conductivity
Measure of speed with which heat moves through substance
Greater thermal conductivity means substance better conducts heat
Thermostabilization
best achieved by constructing vaporizer with high thermal conductivity ie bronze, copper
If vaporizer has wicks, must be in contact with metal part so heat loss through vaporization can be quickly replaced
What are examples of measured flow vaporizers?
Copper kettle, Desflurane, Ohio #8
What are three components of measured flow vaporizers?
vaporizer, vaporizer flow meter, bypass flowmeter
Measured Flow Settings, Compensation
- Require temperature compensation via flow control
-Often require algebraic conversion or slide rule to determine ratio of vaporizer setting to bypass flow
What are the methods of vaporization?
- Variable Bypass
- Flow Over
- Bubble Through
- Injection
What is the main purpose of a variable bypass vaporizer?
VP anesthetic agents > partial pressure required to produce ax
* Must have way to dilute amt of VA being delivered to patient
* Accomplished by splitting gas through vaporizer
MOA variable bypass: splitting valve
- determines how much of FGF goes through bypass vs into vaporizing chamber
- Come together at vaporizer outlet to enter BS
Splitting ratio
vaporizing chamber FR/bypass FR
Depends on ratios btw two pathways, which in turn depends on adjustable orifice = outlet of vaporizing chamber
Also depends on total flow to vaporizer
MOA: flow over
Carrier gas passes over surface of liquid
Requires compensation: changes in gas FR through vap = changes in output
Ex: if excessively high flow, complete saturation of gas moving through vaporizing chamber may not occur so decreases output
Increased surface area of gas-liquid interface, increased efficiency of vaporization
Strategies of flow rate compensation?
–Increase surface area of carrier gas-liquid interface to ensure full saturation of gas exiting vap chamber
MOA:
–Baffles, spiral tracks – used to lengthen gas pathway over liquid (Tec 5)
– Wicks increase SA of liquid through capillary action, must have bases IN liquid anesthetic
MOA bubble through
Carrier gas bubbled through liquid via diffuser
MOA injection
Inject known amt of liquid anesthetic into known vol of gas
VOC?
High resistance, prevents pressurizing effect
VIC?
Low resistance
Agents with low VP (methoxyflurane) or potency (ether)
Affected by minute vol, FGF, PPV, temp
3 ways achieve temp compensation
- Construct vaporizer out of materials that supply/conduct heat efficiently so act as ‘sink’ from atmosphere, greater thermostability
- Suppled heat
- Alter splitting ratio so that increase GF as temperature decreases/decrease GF as temp increases
MOA supplied heat
electric heater used to supply heat to vaporizer
Computerized thermocompensation
Changing amt of liquid injected, heat loss DT vap may not be important
Altering flow of carrier gas through vaporization chamber
All done electronically
Mechanical Thermocompensation
- Compensates by altering splitting ratio
-Main principle: liquids/metals contract when get cold, expand as warm
So as vaporizer cools, the thermal element allows more carrier gas to pass through vaporizer
Why does the vaporizer decrease in temperature?
For vaporization to occur, anesthetic molecules have to escape from liquid and become vapor –> reduces energy of remaining liquid
More molecules escape (become vapor), more energy lost from liquid
As vaporization happens, falling temp/lowering energy of liquid = less vaporization = decrease concentration of anesthetic being delivered
What are the 3 strategies of mechanical thermocompensation?
- Liquid bellows
- Metal rod
- bimetallic strip (Tec series)
Agent Specificity
Most modern vaporizers = agent specific
Multipurpose: Ohio #8, Stephens
Resistance
- Plenum
- Draw Over
Plenum
High resistance, unidirectional, agent specific, variable bypass vaporizers, VOC
Draw Over
Low resistance
inefficient vs plenum
Robust, portable - good for field ax
Concentration Calibrated
Calibrated by agent concentration expressed in % of vapor output
Vaporizer output controlled by single knob or dial that calibrated in volumes percent
Designed to be btw FM, common gas outlet
o NOT for use btw common gas outlet, BS – cannot handle high FGFs of O2 flush, will increase resistance
Effects of barometric pressure
Most calibrated at sea level, ASTM standards: effects of changes in ambient pressure on performance included in manual
What happens with back pressure?
Occurs during IPPV, O2 flush activation
positive pressure transmitted back from BS to machine, vaporizers = increased or decreased outflow from vaporizer
What is the pumping effect?
Increased vaporizer outflow due to : positive pressure breath causes transmission of back pressure to vaporizer, thus back pressure opposes gas flow out of vaporizer chamber and bypass
MOA Pumping Effect
FGF entering vaporizer retrograde gets compressed
Size of vapor chamber > bypass, more gas gets compressed in vaporizer chamber
That excess gas in vap chamber collects vapor
When pressure released, goes all directions including retrograde into bypass tract so now, delivering vapor from both vaporizing chamber and bypass tract = OVERDOSE
Contributing factors to pumping effect
less agent in vap chamber (vaporizer less full), carrier gas flow low, pressure fluctuations high/frequent, dial setting low
Which type of flow is Assoc with pumping effect?
LOW carrier gas flows
Strategies to reduce pumping effect
Reduce size of vaporizing chamber relative to bypass chamber
decreases amt of pressurized gas reaching vaporizing chamber
Long spiral, small-diameter tube to connect vap chamber to bypass channel (Drager 19.1)
amt of pressurized gas reaching vaporizing chamber
One way check valves immediately upstream from vaporizer
Sometimes used downstream O2 flush: prevent back pressure assoc with use
Exclude wicks from area where inlet tube joins vaporizing chamber
Overall increase resistance (?) of gas flow through vaporizer
Pressurizing Effect
essentially dilutes out anesthetic agent, decreases outflow
pressure to vaporizer outlet causes increased pressure to vaporizer chamber -> compression of carrier gas molecules so that more molecules of carrier gas per mL
Number of vapor molecules in chamber DOES NOT CHANGE bc vapor pressure depends solely on temperature, NOT ambient pressure
Same molecules of vapor in more molecules of carrier gas = decreased concentration of anesthetic in chamber/outlet
Contributing factors to pressurizing effect
high flows, large pressure fluctuations, low vaporizer settings
Which type of flow is assoc with pressurizing effect?
High flows
Effects of Rebreathing?
Vaporizer dial setting = reflects concentration of inhalational agent delivered to BS
If little to no rebreathing: Fi(inhal) ~ Et(inhal)
As decrease FGF, exhaled gases = more significant portion of inspired gases –difference btw vaporizer setting, inspired concentration
Increased minute volume -> increased rebreathing = greater effect
Need agent analyzer to determine inspired agent concentration
3 ways to fill vaporizers
- Standard screw capped filler port/funnel fill system - pour into vaporizer chamber
- Agent specific keyed port - prevents inadvertent filling of vap with wrong ax, grooves specific to agent
- Quik-Fill system (sevo, maybe iso): bottle pushed into vaporizer component, valve opens allowing filling
How to fill desflurane vaporizer
All vaporizers use same bottle to fill vaporizer
Crimped on adapter that has spring loaded valve that opens when bottle pushed into filling port
When bottle removed, valve on bottle closes to prevent agent spill
Filling port has spring valve to prevent agent from escaping
Mounting Systems
Back bar, rail or mounting system used to hold vaporizers on machine
Cagemount systems in vet med: 23mm taper push fittings (inlet, outlet; female, male) to attach vaporizer to gas delivery system, vaporizer bolted directly to back bar
- Permanent
- Proprietary Systems
Pros of permanent mounting
Less physical damage to vaporizers
fewer leaks
always filled in vertical position
Cons of permanent mounting
Machine may not have enough mounting locations to accommodate all needed vaporizers
Malfunctioning vaporizer cannot easily be exchanged
Pros of proprietary mounting systems
–More compact machine with fewer mounting locations
–Vaporizers can be easily removed, replaced even during a case
–Can remove vaporizer if have MH
What are the two proprietary mounting systems?
- Selectatec
- Drager
Cons of proprietary mounting systems
–Partial or complete obstruction to gas flow from problems with mounting system
–Leaks, absent/damaged o-ring
–Leaving walking lever in unlocked position
–Compatibility challenges among different manufacturers
MOA Selectatec Mounting System
–Two vertically situated male valve ports
–Btw inlet, outlet port = accessory pin, locking recess
–Compatible vaporizers: two female ports with recessed assembly to receive accessory pin
–Vaporizer lowered onto male port, locked into place via locking knobs > cannot turn vaporizer on if not locked
–O rings on male valve ports ensure gas-tight seal between vap, Selectatec mount
–Loss, deformation of rings: leaks btw vaporizer, mount
–When vap turned on, retractable spindle depresses ball valve in male valve ports allows gas to flow from vap to ax machine
Safety Interlock System
(vap exclusion/isolation) : horizontal push rod system, ensures only one vap turned on at a time
What are the safety checks that should be performed following attachment of a vaporizer?
–vaporizers should be level, at the same height; –attempt to lift each off without unlocking
–can only turn on one at a time
Maintenance
Required – model specific, follow manufacturers recommendations, responses of patients, suspicion that dialed concentrations erroneous, any component improperly functioning
o Evaluation of operation
o Cleaning
o Changing of filters
o Replacement of worn parts
o Calibration
What is important about maintenance of vaporizers specifically for halothane, methoxyflurane?
preservatives that not highly volatile, collect in vaporization chambers/on wicks (gunk up vaporizer)
o Potential to affect ax output
o Vaporizers must be periodically drained to remove preservative accumulation
Previously: recommended flushing vaporizer with diethyl ether to dissolve
No longer recommended: 100% oxygen as carrier gas, diethyl ether = flammable
What is the preservative in halothane?
Thymol
What is the preservative in methyloxyflurane?
butylated hydroxytoluene
ASTM Standards: effects of variations?
- Effects of variations in ambient temp and pressure, tilting, back pressure, input flow rate, gas mixture composition on performance must be stated in accompanying documents
ASTM Standards: settings
Shall not deviate >20% or 5% of maximum setting without backpressure
Shall not deviate more than +30/-20% or more than +7.5/-5% of maximum setting with pressure fluctuations at common gas outlet of 2kPa with total flow of 2L/min or 5kPa with 8L/min
ASTM standards: how much emit in off position?
<0.05%
ASTM standards: vaporizer filling
- Max and min filling level must be visible
- Cannot be overfilled in operating position
ASTM standards: in what direction should a vaporizer open?
Counter clockwise
ASTM Standards: fittings
- Out of circuit must have 23mmfittings, male on inlet, female on outlet
- In circuit must have 22mm fittings, female on inlet, male on outlet; must be marked for use in breathing system
- Direction of gas flow must be marked
ASTM Standards: flow of gas btw vaporizers
- Must prevent gas from going through one and then another vaporizing chamber
Hazards: tipping
o If tip sufficiently, liquid from vaporizing chamber may get into bypass or outlet - high concentration delivered when vaporizer first used
o Should tipping occur high flow of gas run through vaporizer with concentration dial at low concentration until output shows no excessive agent
o Many new vaporizers: mechanism that blocks entrance/ exit from vaporizing chamber prevents problems associated with tipping
How prevent tipping
Mounting vaporizers securely, handling with care when not mounted
Turn off or in travel setting before movement
Hazards: overfilling
–If overfilled, liquid agent may enter fresh gas line -> Deliver high concentrations or cause complete vaporizer failure (no output )
Most vaporizers: filling port situated so that cannot occur, liquid pours out of funnel first
–can happen with agent specific filling devices
Always fill in vertical position securely attached to anesthesia machine
Hazards: what happens if put anesthetic with lower SVP in a vaporizer made for an agent with a higher SVP?
lower than indicated ax output (=underdose)
Hazards: what happens if put anesthetic with higher SVP in a vaporizer made for an agent with a lower SVP?
higher than indicated ax output (=overdose)
Since halothane and isoflurane have similar SVP, can you use halothane and isoflurane vaporizers interchangeably?
SVP halothane = 243, iso = 240
halothane vaporizers can produce concentrations of iso reasonably close to dial settings for halothane
–Iso in halo vap 20-50% more vapor than expected
–Halo in iso vap lower than expected delivered concentration
–Vap needs to be completely recalibrated for iso
Hazards: reverse flow
In most cases will be increased output
Consequences of reversed flow particular to vaporizer
Hazards: leaks
Effect depend on size, location; whether have check valve at vaporizer outlet
Common cause of leaks equals failure to replace or adequately tightened filler cap
o Leak will result when vaporizer turned on
Vaporizer may not be mounted properly, fitting btw vaporizer and inlet/outlet connection may become loose or broken
What if have leak in vaporizer connection or mount?
machine function normally until turn vap on
At that point, FGF from machine lost through leak -> total flow reduced
Consider leak if refilling vaporizer with unusual frequency, odor detected, or loss/reduction of FGF into breathing system after vaporizer turned on
Hazards: vapor leak into FG line
Some vaporizers leak small amounts of vapor into bypass when turned off
Amount of leak depends on ambient temperature, sizes/configuration of internal ports
Leaks reduced by not turning vaporizer from off to the zero setting unless being used
Hazards: physical damage
shock excessive vibration or mistreatment may lead to malfunction
Less common with permanently mounted vaporizers
Hazards: contaminants in vaporizing chamber
Water, other substances cause corrosion - contact manufacturer to determine action
hazards: projectile
Vaporizer may be MRI compatible but only when attached to machine
Tec 3 classification
Variable bypass, flow-over with wick
Automatic thermocompensation
Agent specific
High resistance
Back pressure compensated
Tec 3: thermal compensation
bimetallic strip
Tec 3: back pressure compensation
long tube leading to vaporization chamber, expansion area in tube, exclusion of wicks from area of vaporization chamber near inlet
Tec 3 accuracy
Output = nearly linear over range of concentrations, flow rates: 250mL/min-6L/min
Tec 5 classification
Variable bypass, flow over the wick
Automatic thermocompensation
Agent specific
high resistance
Back pressure compensated
Differences btw Tec 3 and Tec 4?
o Safety interlock system: vaporizer isolation/exclusion when multiple vaporizers mounted in series
Accuracy of Tec 5
Greatest accuracy <5Lmin, <3% setting, 15-35*C
Less output if higher flow or dial setting)
Less output if <15, more output if >35
Tec 5 temp compensation
bimetallic strip located in bypass channel
As temp decreases, less gas allowed through bypass channel (bypass channel is on bottom)
Tec 5 internal baffle system
keep liquid from reaching outlet if vaporizer tipped, inverted
Tec 5 Spiral Wicks
Gas flowing into vap chamber first passes through central part of rotary valve
Directed through helical channel past spiral wick in contact with wick skirt that dips into liquid agent
Gas with vapor leaves chamber via channel in concentration rotary valve, flows to outlet
Tec 5 Agents
enflurane, isoflurane, sevoflurane, halothane
Tec 4
Isoflurane only
Temp compensation = bimetallic strip
has Selectatec mounting bar
Tec 5 filling mechanisms
2 - keyed system, drain plug
Tec 5 Hazards
gas leak if locking lever loose or filling port open; overfilling possible if bottle adaptor loose/control dial on
Tilting -> overfilling -> increased vapor output
Reversed flow through vaporizer increases output
Tec 7 Classification
Variable bypass, flow over the wick
Automatic thermocompensation
Agent specific
High resistance
Back pressure compensated
Obligatory Selectatec mounting bar
o Essentially same MOA as Tec 5
Safety interlock system
Filling Mechanisms Tec 7
Three filling mechanisms: funnel fill, Quik-Fil, easy-Fil
~300mL liquid needed to fill vaporizer with dry wicks, ~75mL retained in wicks when drained
Tec 7 Vaporizer Identification Label
on back: used by systems with vaporizer identification units
Accuracy of Tec 7
Greatest accuracy: FGF 5L/min, <3%, 15-35*C
o Higher flows, higher dial settings: decreased output below set value
Thermostat does not respond to <15C
Temp >35C = unpredictably high output
Maintenance of Tec 7
drain 1x yr, halothane drained Q2 weeks if additives/stabilizing agents; service 3yr from purchase then Q6mo
o Clean external surfaces with damp cloth
Penlon Sigma Delta Classification
Variable bypass, flow over with wick
temperature compensated
high resistance
agent specific
VOC
Penlon Sigma Delta Agents
sevo, iso, des, enflurane
Penlon Sigma Delta Filling
Three different filling devices: funnel fill, keyed fill, Quik-Fil
Liquid capacity 250mL, 60mL remains in wick after drain
o When filled to minimum mark = 35mL
Penlon Sigma Delta Accuracy
Accuracy: 15-35*C, FGF 0.2-15L/min
o Temp-compensating mechanism slow, may need minimum 1-2hr to compensate
o Steady back pressure of 10-15kPa/100-150 cm H2O decreases vaporizer output
Effect greatest at low vaporizer settings, low FRs
Calibration of Penlon Sigma Delta
Calibrated with 100% oxygen
o Nitrous oxide: decreases output
o Air: decreases output <5%
Penlon Sigma Delta Maintenance
Calibration with suitable agent gas analyzer – must service if outside limits
Major service Q10yrs, halothane Q5yr with periodic draining
Hazards: pennon sigma delta
Store btw -20C and 50C, malfunction if exposed to higher temperatures
Control dial zero, vaporizer upright during filling – otherwise possible to overfill
Overfilled vaporizer requires manufacturer eval
How to transport/manage the Penlon Sigma Delta while filled
0 (ideal): sit for 10’ once reconnected to machine
* Ax agent overdose if not enough time for any liquid to drain to normal position
Open: 5L/min x >10min
Tipped, interverted: dial max, 5L/min, >10min
Fluotec Mark 2
Poor Performance
Tec 3
Variable bypass, flow-over with wick, automatic thermocompensation, agent specific, high resistance, back pressure compensated
o Temp: bimetallic temp-sensitive element assoc with chamber
o Back pressure: long tube leading to vaporization chamber, expansion area in tube, exclusion of wicks from area of vaporization chamber near inlet
Examples TEC 3
Flutec Mark 3, Pentec Mark 2
What did the TEC4 introduce?
Safety Interlock System
General MOA of variable bypass vaporizers?
Split carrier gas to flow in vaporizing chamber where picks up ax vapor or goes to bypass change
Percentage vol of a gas
= partial pressure of gas/total pressure of air x 100%
Ex: iso SVP 240mm Hg, atmospheric pressure = 760mm Hg
240/760 x 100 = 31%
What type of vaporizer are the Desflurane vaporizers?
Measured flow
Are most vaporizers electronically powered?
No - mechanical devices, no external power to function normally
Electronic Vaporizers
Aladin cassette vaporizer (human med)
Vetland EX3000 Electronic Vaporization System
Electronic variable bypass or electronic injection type
Electronic Variable Bypass vaporizers
splitting ratio of carrier gas determined electronically instead of mechanically
Rely on properly operating electronics to function
Computer calculates carrier gas flow needed to pass through vaporizing chamber in order to produce desired anesthetic agent concentration
Electronic Injection Type Vaporizers
withdraws calculated amount of liquid agent from agent bottle, injects liquid into breathing system or fresh gas flow
Amount of liquid injected adjusted to achieve desired anesthetic concentration
In a variable bypass vaporizer, what is the final concentration of gas determined by?
Ratio of amt of gas that picks up inhalant to gas to gas that bypasses inhal
Vapor pressure of VA
Drager Vaporizer 19.1
- Variable bypass, flow over the wick, automatic thermocompensation, high resistance, agent specific, pressure compensated
Inhalants used with Drager 19.1
Iso, enflur, sevo, halothane
Accuracy of Drager 19.1
- 10-40oC operating range, accuracy 10%
- Accurate FGF 0.3-15L/min, complete saturation may not occur at higher flow (output falls)
Does mounting effect output with Drager 19.1?
No
What gas is used to calibrate the Drager 19.1?
Air
With 100% oxygen, delivered concentration 4-10% higher than set
Drager 19.1 Hazards
- Hazards: tilting spill into control device, increase or decrease delivered concentration
Drager 19.1 - why increase in popularity?
1st popular in large animal – significantly larger inhalant reservoir capacity vs Tec 3, 4
Difference btw Drager 19.1 and 19.3?
19.3 – interlock model
Maintenance of Drager 19.1
outside wipe down damp cloth with detergent, maintenance Q6mo, chamber cleaned/wicks changed Q2yrs
o Halothane: rinse with fresh halothane when liquid in sight glass shows discoloration, particles
Drager Vapor 2000 - main difference
Handwheel: “T” transport position – used when vaporizer removed from ax machine
o Pin on locking lever must engage with groove in top of handwheel to release vaporizer, only happens in T position
Three isolation valves
Vents excess FGF to outside when vaporizer not on
Ohio Calibrated Vaporizer
- NOT same as Ohio #8 (Boyle’s Bottle)
- Variable bypass, flow over with wick, automatically temperature compensated, agent specific, VOC, high resistance
Agents used in Ohio Calibrated Vaporizer?
- Isoflurane, halothane, sevoflurane
Accuracy of Ohio Calibrated Vaporizer?
- Accuracy at FGF 0.3-10L/min, temp compensation btw 16-32*C
Tipping with Ohio Calibrated Vaporizer
o No problems if tilt up to 20* while in use, up to 45* not in use
o More tipping > delivery of higher concentrations
Other Considerations with Ohio Calibrated Vaporizer
Plastic spacers btw paper wicks, may react with enflur or iso > discoloration of liquid, not problematic
Measured Flow Vaporizers
No longer being manufactured, not covered by ATSM standards for equipment – precursors to today’s modern variable bypass vaporizers
Measured -flow, bubble-through, high resistance, VOC, temperature compensated (thermally stable with manual flow adjustments based on temperature of liquid, multipurpose
Features of Measured Flow Vaporizers
Back pressure – check valves
Can vaporize halothane, isoflurane, sevoflurane, or methoxyflurane in same vaporizer > need to be clearly labeled for the agent in use
Able to retrofit check valves
Manual adjustments required for variations in total gas flow, day to day temperature changes, changes in liquid temp during use, especially with high FGF
Functions of the two flowmeters in a measured-flow vaporizer?
One routes all oxygen through vaporization chamber where it is fully saturated
The other bypasses to meet patient requirements
Operator must manipulate both to achieve the proper anesthetic concentration
What are the two historical measured flow vaporizers?
copper (Copper Kettle) or silicon bronze (Verni-Trol)
What are the three Desflurane vaporizes?
Tec 6, Drager D, Penlon Sigma Alpha
Classification of Desflurane Vaporizer
Measured-flow, automatic thermocompensation, agent specific, high resistance, back-pressure compensated
Why does desflurane need a special vaporizer?
Des = low potency, low boiling point (~23*C, near room temp) > requires heating to ensure complete, stable vaporization of liquid + accurate vaporizer output
DT low potency, lrg amts required to be vaporized
Warmed to 39*C, pressurizes to 2atm (1500mmHg) – two heaters in base
Injects ax into FGF
Role of Electronics in Desflurane Vaporizer (LJ)
Indicate operational status, level of agent, control pressure balance btw diluent/bypass + vaporized inhalant, to heat liquid desflurane, charge backup battery
Can only turn on once electronics deemed it to be operable
Performs self check every time turns on
Solenoid interlock allows dial, rotary valve to be turned on
Concentration dial of desflurane vaporizer
Concentration dial: 1-18%, 1% gradations up to 10%, 2% btw 10-18
Release to turn on vaporizer cannot be depressed until operational LED on
Release used if >12%
Liquid Level Indicator on Desflurane
Liquid crustal display (LCD), visible when vap on
Indicates amt of liquid in vap btw 50-425mL (total vol of sump = 425mL)
20 bars, 1 bar = ~20mL
Desflurane Vaporizer Filling
while in use if FGF <8L/min/dial <8% (no high back pressure) or while warming up
Only desflurane-specific bottle inserted into filler port
Accuracy of desflurane vaporizer (not in LJ)
0.2-10L/min, temps 18-30*C
o Tilting does not render vaporizer inactive/dangerous to operate
o No effect from fluctuating back pressure unless high while filling
o Carrier gas affects output: air, N2O output
o Electricity consumption low
What is important about the desflurane injection rate vs FGF?
THEY MUST BE MATCHED
Hazards of Desflurane Vaporizer
–Vapor can leak into FGF when off
–If used on ax machine that turns off FGF during inspiration (FG decoupling, eg Fabius), intermittent flow will trigger alarm if software to avoid not in place
–Assoc with electronics:
Sparks, smoke if plug loose
Mounted on R side of back bar of machine so power cord does not interfere with vaporizer interlock mechanism for other vaporizers
Humans: CPA following massive overdose DT defective control valve
Maintenance of Technicians 6
service Q1yr at authorized center, wipe external surface with cleaning agent
Advantages VIC
low cost
Simple design
Portability
Nonspecific to agent
Low resistance to air flow
Low gas flows (minimizes amt of agent required, cost, atmospheric pollution)
Disadvantages VIC
Not precise
unpredictable
Nonspecific to an agent
No compensatory mechanisms
Inhalants with high SVPs not good candidates
o Lower SVPs (methoxyflurane) less likely to produce overdose
Vaporiing Chamber
simple reservoir with a glass, allows provider to determine amount of liquid present +/- temperature compensation
VIC: what affects output?
vaporizer dial setting, FGF, composition/concentration of gas entering vaporizer next line
In turn, depends on patient minute vol, oxygen-ax agent uptake, BS configuration
Where VIC usually located in circuit?
Btw inhalation valve, patient
Ambient Air in VIC
Ambient air often used as principal carrier gas, can use oxygen with T piece
o Inspired oxygen [ ] depends on oxygen flow, reservoir volume, ventilatory volume
Two MOA of VIC?
- Push Through
- Draw Over
Stephens Vaporizer
glass bottle, flow through or bypassing controlled by central control graded in settings 0-8
At 0, all gas bypasses vaporizer
At 8, all gas passes through vaporizer
Adjustable metal sleeve – altered to proximity of gas entering vap chamber to surface of liquid anesthetic (similar to a wick)
Komesaroff vaporizer
no adjustable sleeve, smaller liquid anesthetic surface area
