AGM Exam Flashcards
Gas machine MAIN purpose
deliver O2 to pt
Gas machine 2nd purpose
deliver means of positive pressure ventilation
Gas machine 3rd purpose
deliver anesthetic gas to pt
Key safety features for AGMs
BATTERY BACKUP, alarms, monitors, flow meter controls
MOST IMPORTANT key safety feature
BATTERY BACKUP ~30mins
Oxygen’s 5 Tasks ( gas machine purpose founded on this)
-ventilator driving gas
-flush valve
-O2 pressure fail alarm
-O2 pressure sensor shut off valve (fail safe)
-drive flowmeters
_ - _ _ measures amount of potent inhaled anesthetic agent to be added
concentration-calibrated vaporizer
_ deliver a controlled gas mixture in terms of concentration of o2 and other gases and total gas flow rates via gas flow controls
Flowmeters
Fresh gas mixture of known composition and metered production leaves anesthesia machine at :
CGO
The _ _ is a minienvironment that allows respiratory exchange and control of anesthetic and respiratory gas tensions
Patient Circuit
Anesthesia ventilator _ or _ may be connected to breathing circuit to provide mechanical ventilation
bellows or pistons
Excess gases are vented from breathing circuit and at end-exhalation when not using a ventilator via the _ _
APL valve
Excess gases are vented from breathing circuit and at end-exhalation when using a ventilator via the ventilator _ _ valve
ventilator pressure relief valve
SPDD stands for?
Supply Processing Delivery Disposal
Using SPDD model, where does supply occur on AGM and what components are involved?
Site: back of machine
Components: pipeline and cylinder
Using SPDD model, where does processing occur on AGM and what components are involved?
Site: within AGM, proximal to CGO
Components: Failsafe, Flowmeters, Flush Valves
Using SPDD model, where does Delivery occur on AGM and what components are involved?
Site: Breathing Circuit
Components: Hose, CO2 Monitors
Using SPDD model, where does Disposal occur on AGM and what components are involved?
Site: Scavenging System
Components: Scavenging System
The high pressure system of the AGM starts and ends where?
Start- Cylinders
End- AGM Pressure Regulators
O2 tanks have standards written by the US _ and are made of _ typically.
DOT, steel
O2 tanks that are MRI safe are made of _
aluminum
O2 tanks are tested every _ years to _ times their service pressure
5 years, 1.66 x service pressure
What is the PSI of O2 and does it follow Boyle’s Law?
1900 PSI, yes
What is the PSI of N2O and does it follow Boyle’s Law?
745 PSI, No
What is the PSI of Air?
1900 PSI
What is the capacity of an O2 tank?
660L / tank
What is the capacity of an N2O tank?
1590L / tank
What is the capacity of a tank of Air?
625L / tank
What is the Pin Position of O2?
2-5
What is the Pin Position of N2O?
3-5
What is the Pin Position of Air?
1-5
What is a way to determine accurately how much N2O is in tank?
Weigh it;
Full tank = 20.7lb
Empty tank = 14.1lb
O2 exists as a gas @ room temp in a tank because its critical temp is _*C
-118*C
A half empty tank of O2 will have a capacity of _ L and a pressure around _ PSI
330L and 1100 PSI
Critical temp is the highest temp in which a substance can exist in a _ state REGARDLESS of pressure applied
liquid
N2O has a _ relationship with volume and pressure
non-linear
T/F:
When N2O tank is full some of its contents are in gas and liquid state?
true
The critical temp of N2O is _ *C which is _ room temperature and this is why it exists in 2 states in a pressurized tank.
36.5C, above room temp =20C
When to change N2O tank?
if PSI is anything less than 745 change ASAP
O2 tanks = green
N2O tanks = blue
Air tanks = yellow
but best way to check tank contents is to _ _.
Read Label
The vaporizers would be which part of the SPDD model?
Processing
Which 2 instances to open tanks on machine?
-machine checks
-emergency use
WILL DEPLETE IF LEFT OPEN AND BE EMPTY IF EMERGENCY HAPPENS
The 2 safety devices on the tank in case of fire or high pressure could be:
Frangible Disk - ruptures under pressure
Woods Metal (BLTC) bismuth, lead, tin, cadmium- fusible plug that melts >150-170*F
Most delicate part of tank?
valve
Hissing tank troubleshoot steps: (moving forward if problem isn’t solved)
1) tighten check valve on back on yoke- use yoke plug to tighten
2) get new washer
3) ensure hose connection are ok
4) get a whole new tank
N2O tank will always read 745PSI until it is about _ empty
3/4
Goal of correct gas placement is correct cylinder onto correct _.
yoke
How can PISS system be bypassed?
more than 1 washer on a cylinder
When to replace washer?
when changing cylinders bc heat from inlet can warp washers
What could happen if there is no washer on a cylinder?
a leak if it is open
Intermediate Pressure System starts and ends where?
Start- pipeline
End- flowmeter VALVES
Intermediate Pressure System:
Pipeline > Pressure Gauge > _ _ > Failsafe > _ _ _ _ > 2nd stage Regulator > _ _ _ > Flowmeter Valves
-check valves
-O2 supply failure alarm
-O2 flush valve
High Pressure System:
Cylinder > _ _ > Check valve > _ _ _ > Cylinder Pressure Regulator
-Hanger Yoke
-Cylinder Pressure Gauge
The check valve on the hanger yoke’s purpose is to:
ensure unidirectional gas flow if gas source pressure is less than machine’s
Each gas tank-yoke connection has a regulator valve that reduces the cylinder’s PSI down to _ PSI
45
-this is to ensure gas is preferentially pulled from pipeline if cylinder is open
The pressure regulator on the yoke/tank connection reduces tank PSI to 45 because pipeline pressure is _ PSI
50 PSI
If tanks were left open while using wall source too and low O2 alarm sounds, what happened?
There was a loss of pipeline pressure and your AGM was seamlessly drawing O2 from opened tanks which you now realize are EMPTY and you’re screwed
If tanks were closed while using wall source and low O2 alarm sounds, what happens next?
You have time to switch open and use backup tanks for O2, with plenty of time to get new tanks until wall source issue is solved
Equation to see how much O2 left in cylinder:
[Total Capacity (L)/ Full Tank Pressure (PSI)] X ( Y(L) / current Gauge Pressure (PSI)
OR (bc O2 capacity/full pressure = ~0.35)
0.35 X [Y (L) / gauge pressure (PSI)]
Equation to see how long O2 tank will last:
Contents Remaining (L) / FGF (L/Min) = X
The pressure gauge on O2 tank reads 600 PSI and you’re running it at 2L/min, how many more minutes do you have before tank runs out?
0.35 = (X/ 600)
210L left
210L/ 2= 105 minutes
Pressure gauge on O2 tank reads 500PSI, running at 6L/min, how much time is left before tank is empty?
0.35 = (X/500)
= 175L
175L / 6L/min= 29.1 ~ 29 mins left
Pressure gauge on O2 tank reads 350PSI, running at 4L/min, how much time is left before tank is empty?
0.35=(X/350)
= 122.5L
122.5/4 = 30.625 = 30mins
What safety system is in place to prevent inadvertent misconnection of gas cylinders to the anesthesia machine?
PISS
The pressure change that happens as Oxygen from the cylinder enters the pressure regulator is from ___ to ____?
1900 - 45PSI
T/F The pipeline is part of the high pressure system
false- intermediate
What is the working pressure of the AGM?
50 PSI
T/F there are pressure gauges and check valves on both the high pressure system and the intermediate pressure system prior to entering the AGM
true
T/F DISS system is for the cylinders and the wall source pipeline
false, just the wall source
What pressure will trigger the O2 supply failure alarm and what does it mean?
<30 PSI
-pipeline failure, hose disconnection, OR tank is almost empty
What O2 pressure will trigger Failsafe valve on N2O/Air to lower or completely stop flow?
<20 PSI of O2
In the intermediate system, with GE AGMs what will the failsafe valve do if O2 drops below 20PSI?
It will completely shut off flow of N2O
In the intermediate system, with Drager AGMs what will the failsafe valve do if O2 drops below 20PSI?
It will proportionately lower flow of N2O to the flow of O2
How can a hypoxic mixture still occur even with a failsafe valve?
If there is a pipeline crossover/ leak because the failsafes are only PRESSURE sensitive
-the flowmeter is further downstream too and won’t detect a leak at first
What is the pressure and flow when using the O2 flush valve on AGMs?
50 PSI and about 35-75L/min
T/F You can use O2 flush valve while hooked onto breathing circuit with a patient to decrease anesthetic agent concentration because it bypasses vaporizers.
FALSE! Holy barotrauma!
-Must disconnect from pt 1st to “flush it”
O2 Flush valve can be used to:
-pressurize circuit during a machine check
-set up AGM
-during a facemask leak ( put volume back in circuit)
-flush out agent if pt is hypotensive (once disconnected from pt!!)
-AND_
flush machine at end of case to remove agent
The primary driving gas in the ventilator power inlet of the AGM is _ and it helps push bellows _ during + pressure vent.
O2, down
T/F Using ventilator while using a tank to supply O2 doesn’t affect speed of O2 depletion.
false, uses O2 more quickly
The pipeline pressure regulator(2nd stage pressure regulator), which isn’t in every model, has a goal to reduce pressure to _ PSI so flow is smooth before entering flowmeters.
16-26PSI
The Low Pressure System starts and ends where?
Start- Flowmeter Tubes
End-CGO
What are 2 appropriate steps with suspected pipeline gas crossover?
1) Turn on backup cylinder
2) Disconnect O2 pipeline ASAP
What safety system is in place to avoid inadvertent connection of gas hose to anesthesia machine?
DISS
Pressure change that occurs at the DISS system:
Pipeline pressure -> 50PSI; higher than Cylinder change
During a machine check you inadvertently leave the o2 cylinder open. Approximately 1 hour into your case, pipeline pressure is lost. The failsafe alarm sounds. You go to open the oxygen cylinder, realizing it is open. What is the consequence of this action?
O2 Cylinder is EMPTY, call for help for backup O2 source ASAP :(
The failsafe device located in the intermediate pressure system consists of what 2 components?
-O2 Supply Failure Alarm
-Failsafe Valve
Low Pressure System consists of: (4things)
-flowmeters / thorpe tubes
-vaporizers
-one way valves
-CGO
T/F Turning a flow meter control knob clockwise will increase the O2 flow.
False!
-Turn it COUNTERclockwise to increase flow
Traditional flowmeters use a needle-valve mechanism and its O2 tube is _ and _ and is located on the _ side.
O2 tube is larger and fluted
found on far right side
Pros / Cons to electronic flow valve control mechanisms on AGM:
Pro: precision of O2 control, less expensive, collects data
Con: requires electricity/ battery power
T/F The flowmeter is the knobbed device used to adjust flow levels
false, it is not the knob itself, but the meter in the tube that measures the flow (float goes up/down)
Position of the float (bobbin or ball) on the flowmeter tube is determined by which 2 forces?
-FGF pushing it up
-Gravity pulling it down
Thorpe tubes (old school flowmeter tubes) are made of _ to prevent buildup of _ _ and they are more narrow at the _ and wider at the _.
-glass
-static electricity
-narrow at bottom
-wide at top
In thorpe tubes the _ _ is the space where gasses pass around between the bobbin and inside of the tube wall
annular ring
In flowmeters, low flow gases are influenced by the _ of the gas and favors _ flow.
Viscosity, Laminar Flow
In flowmeters, high flow gases are influenced by the _ of the gas and favors _ flow.
Density, Turbulent Flow
T/F In higher altitudes, flowmeters will read higher than the actual flow set.
False, will read LOWER because of LOWER atmospheric pressure
To read flowmeter accurately, red the flow at the _ of the bobbin or _ of the float ball.
Top of Bobbin, Middle of Float Ball
In which ways can a flowmeter tube not be accurate?
-debris in tube
-high altitude
-tube becomes misaligned somehow
-if bobbin gets stuck at top
-crossover of gas (calibrated for each gas individually)
-leak in tube
What is the safety mechanism of the O2 flowmeter sitting farthest right?
-last thing going to pt in manifold (last defense of hypoxic mix)
-will still be part of mix if there is a leak or crack in other tubes
If a leak in the flowmeter or manifold area is suspected what actions should you take?
-Just call Biomed and get a new AGM; can’t even see issue without removing panels
How are O2 Pressure Failure Device and Hypoxia Prevention Safety Devices different?
O2 Pressure Failsafe Device - shuts off/reduces N2O if <20PSI of O2, PRESSURE SENSITIVE
Hypoxia Prevention (O2/N2O Proportioning) Safety Device- adjusts levels of N2O/O2 to ALWAYS give at least 25%FiO2; FLOW SENSITIVE
How can hypoxic mix still be given to pt with AGMs that have O2/N2O Proportioning Devices?
-pipeline crossover
-leak distal to the flowmeters
-using a 3rd gas
-defective machine/ pneumatic parts
The 2 main models of AGMs have different mechanisms of O2/N2O proportioning (hypoxia prevention) safety devices and they are:
GE: Link 25 Proportioning Limiting Control System
Drager: O2 Ratio Monitor Controller
The GE Link 25 Proportioning Limiting Control System does what?
hypoxia prevention device
-ensures at least 25%FiO2 is given at flowmeters when N2O is being used
-needs 2nd stage O2 and N2O regulator, uses 14 teeth N2O and 29 for O2 (3:1 ratio)
-INCREASES O2 flow in relation to N2O flow
The Drager O2 Ratio Monitor Controller
Hypoxia prevention device
-limits N2O flow in relation to O2 flow
Gas travels from flowmeters - _ then to CGO
vaporizers
Which part of the AGM is the interface between the pneumatic and ventilatory systems?
CGO
T/F CGO is considered the last part of the low pressure system and they are found on the outside of all AGMs
False, new machines have CGO on inside
T/F The rotameter flowmeter is the narrowest at the top and widest at the bottom
false
The high-pressure system of the anesthesia workstation begins at the ___ and ends at the ____.
cylinder, pressure regulators ( reduce PSI to 45)
Auxiliary O2 are flowmeters on the side of machine used for supplemental O2 and have a max flow of _ L/ min
10L/min
Equation to calculate FiO2 using Flowmeter:
X= {(Air Flow Rate [L/min] X 21) + (O2 flow rate [L/min] X 100)}/ Total Flow Rate
What is the FiO2 if Air flows at 1L/min and O2 is flowing at 2L/min?
[(1L/min X 21) + (2L/min X 100)] / 3L/min = FiO2
[(21)+(200)]/3L/min = FiO2
221/3 = 73.6 ~74%FiO2
What is the FiO2 if Air flows at 2L/min and O2 is flowing at 3L/min?
(21X2) + (100X3)= 342
342/ 5= 68.4 ~68% FiO2
FiO2 of RA is=
21%
FiO2 of 1L is?
24%
FiO2 of 4L is?
36%
T/F Cylinder pressure gauge is part of intermediate pressure system.
False- high pressure
T/F Pipeline inlets are part of High Pressure System
False- intermediate
T/F Flowmeter Knobs are part of Intermediate System
False, Low pressure System
Which part of the system is this AGM component from?
-Cylinder
high
Which part of the system is this AGM component from?
-Hanger Yoke
High
Which part of the system is this AGM component from?
-Hanger Block/PISS system
high
Which part of the system is this AGM component from?
-Check Valves
HIGH (hanger yoke connection) AND LOW (before CGO) !!
Which part of the system is this AGM component from?
-Cylinder pressure gauge
high
Which part of the system is this AGM component from?
-Cylinder Pressure Regulator
high
Which part of the system is this AGM component from?
-Pipeline Inlet
intermediate
Which part of the system is this AGM component from?
-Pressure Gauges
intermediate (ALL pressure gauges for all gases)
Which part of the system is this AGM component from?
-O2 Pressure Failure Alarm Device
intermediate
Which part of the system is this AGM component from?
-O2 2nd Stage Regulator
intermediate
Which part of the system is this AGM component from?
-O2 Flush Valve
intermediate
Which part of the system is this AGM component from?
-Flowmeter Valves
intermediate
Which part of the system is this AGM component from?
-Vent power inlet
intermediate
Which part of the system is this AGM component from?
-flowmeter knobs
low
Which part of the system is this AGM component from?
-needle valves
low
Which part of the system is this AGM component from?
-flowmeter tubes
low
Which part of the system is this AGM component from?
-vaporizers
low
Which part of the system is this AGM component from?
-CGO
low
T/F Vaporizers are closed containers
true
T/F vaporizers convert liquid anesthetic agent into a gas
false - a VAPOR
A vaporized anesthetic agent must be diluted into a _ _
carrier gas
Vapor molecules exerting pressure on walls of their container is the result of _ _
vapor pressure
SATURATED vapor pressure is:
at room temp, SVP is the pressure which an agent is in equilibrium between its molecules entering liquid and entering vapor state
Which anesthetic agent has the highest SVP, making it the most volatile?
Desflurane
-also has low boiling point ~23.5*C
SVP is dependent on the _ and _ of an agent
temperature and nature
-higher temp, higher SVP
-lower temp, lower SVP
T/F There is a linear relationship between SVP and temperature
False
With open containers, evaporation happens _ the boiling point and involves molecules on the _.
Below boiling point, involves surface molecules only (because they escape container)
In closed container, vaporization occurs _ the boiling point and involves the molecules in the _ _
at boiling point, involved all molecules in container
T/F SVP is dependent on the atmospheric pressure, the temperature, and the nature of the agents
False, vapor pressure is INDEPENDENT of atmospheric pressure
Dalton’s Law of Partial Pressure
total pressure = sum of partial pressure of each gas in mix
Heat of Vaporization (Latent Heat of Vaporization)=
number of CALORIES required to convert 1g or 1mL of liquid into vapor WITHOUT a temperature change in liquid
SVP/ atmospheric pressure =
volume of vapor in vapor chamber (%)
Vaporization results in heat loss and decrease in liquid temp, this causes a _ in vapor output
decrease
-vaporizers compensate for this w heating elements
Boiling Point Vaporization
-takes place in vapor itself, molecules break free and bubbles rise to surface
-when Vapor pressure = atmospheric pressure=boiling point**
Specific Heat
number of CALORIES needed for 1g of a substance to increase by 1*C
-reflects heat capacity
Vaporizers are made with material that has a high _ _ to minimize temperature changes
specific heat
Thermal Conductivity
measures how fast substance transmits heat
Modern Vaporizers are classified as: (5 items)
-variable bypass/ calibrated
-agent specific
-flow over
-temperature compensated
-out of circuit vaporizers
On variable bypass vaporizers, adjusting the knob varies how much _ goes into vaporizer vs how much _ it.
FGF, bypasses
T/F When dial on vaporizer is set to 0, no FGF goes thru it at all.
False!
-FGF goes thru vaporizers but it is SPLIT into 2 streams (splitting ratio), would not go thru the vaporizing CHAMBER if set to 0
Both streams of FGF come together and leave vaporizer through the _ _ which is in the common gas _.
outlet port
manifold
Splitting ratios are dependent on: (3 items)
-specific agent
-temperature
-vapor concentration
What safety issue poses a risk with splitting ratios?
-if agents were somehow mixed up, could give dangerous amount of anesthetic bc vaporizers have specific splitting ratios per agent
Sevoflurane:
Desired Anesthetic %- 1%
splitting ratio- 25:1
What does number on left in splitting ratio represent?
How many molecules get sent to BYPASS per 1 molecule that goes to vaporizer
Examples of failsafes to prevent mis-filling vaporizer agent:
-collars on bottles
-funnel fill systems
-key system
Wicks and Baffles help with what inside vaporizers?
Expanding surface area, allowing for more vapor to be picked up by FGF
Methods of thermocompensation in vaporizers:
-bimetallic strips
-metal rods
What do the thermocompensation materials in vaporizers compensate for?
-temperature of OR room
-Latent Heat of Vaporization!!!!!!
In-Circuit Vaporizers
older, more inaccurate, part of circle system
Out of Circuit Vaporizers PRos/ Cons
Pros- accurate, found upstream
Cons- can be tipped, accumulate moisture from exhalation
Prevention of Vaporizer hazards:
-“t” setting during transport to reduce risk of tipping
-new designs not having us pour in agent to refill it
-“keys” for specific agents during refilling
1mL liquid agent =
200mL of vapor, VERY DANGEROUS if spilled/tipped
If vaporizer tips take these actions:
1) drain all liquid from vaporizer and completely flush system (20-30mins) until it detects no more agent prior to next case
If you smell agent in OR what could be happening?
-Leak may be present (check circuit, check if cap is screwed tight on vaporizer)
-Pt could be underdosed!
-Vaporizer was left ON after previous case (do a wash out)
Purpose of interlocking system/rods on AGMS:
only lets 1 vaporizer open at a time
T/F All vaporizers will alarm when they are low.
False, just Des alarms when low
Is a variable bypass vaporizer “in” or “out” of circuit?
OUT of circuit-modern
Which agent has the highest boiling point?
Sevoflurane
What affects vapor output? (4 items)
Gas flow rate
Carrier gas effect
Pumping effect
Pressuring effect
How does FGF rate impact vapor output?
-decreased % at low flows bc not enough turbulence to pick up molecules
-decreased at high flows bc gas passes too quickly to pick up agent
At what rates does vapor output measurement accuracy decrease?
-extremes:
-<200/250mL/min
->15L/min
Carrier Gas Effect:
Air and N2O are more soluble than O2 in liquid anesthetic; gases have diff viscosities and densities that come to play in vaporizer
-when N2O stops, agent will slightly increase in output for a sec
Pumping Effect:
increased back pressure pushes air back to vaporizer, making it more concentrated, more common with low agent conc.
What could be 2 things contributing to pumping effect?
-+ PEEP
-O2 Flush Valve
Safety Mechanisms used to avoid Pumping Effect: (modern AGMs)
-smaller vaporizer/ larger bypass chamber
-long spiral tube to prevent backflow
-backflow check valves
Pressuring Effect:
decrease in vapor concentration due to increased back pressure with high flows
-with high FGF there are same number of vapor molecules and more carrier gas molecules
The Des Vaporizer heats and pressurizes desflurane using a _ _
injection vaporizer, not a splitting effect vaporizer
SVP of Des=
664-669mmHg which is close to atmospheric pressure(760) -no bueno !!
Boiling point of Des
22.8-23.5*C
MAC of Des
6%
Desflurane Vaporizer is gas vapor _ _ blender.
dual circuit
Top Limb of Des Vaporizer allows FGF to flow thru and hit a _ _ (R1), this create back pressure that works as a _ _ valve
fixed resistor, pressure regulating valve
Bottom Limb of Des Vaporizer is connected to the Des reservoir which is a _ of Des _.
SUMP of desflurane liquid
Sump of Des electrically pressurizes it to _mmHg which is _ the atmospheric pressure and heats it to _ *C which is far above its _ _.
1300mmHg-double the atmospheric pressure
39*C,-well above boiling point
The Sump of Des does not shut off until:
Des is at a temperature and pressure that allows for safe / reliable concentration for pt
On the Des Vaporizer there is a _ _ valve that decides how much des goes into the _ _ of the vaporizer.
pressure regulator, bottom limb
Another _ (R2) is part of the lower limb of Des Vaporizer, actual Des vapor exerts pressure on it and it stays balanced in order to keep a _ _.
resistor, working pressure
Output / Working Pressure of Desflurane from Vaporizer is determined by (2 things)
-FGF
-Dial Concentration
The Aladin-Cassette Vaporizer is a permanent electronic vapor control unit in AGMs from which brand?
Datex Ohmeda (GE)
The Aladin Cassette Vaporizer is color coded for each agent and _.
detachable
The Aladin Cassette Vaporizer is a _ _ delivery system, contributing to its accuracy.
closed loop
T/F The Aladin Cassette Vaporizer is adjusted based on dial settings.
False, adjusted based on END TIDAL CONCENTRATION in its closed loop system by its AGENT PROPORTIONING VALVE
What kind of vaporizers are Maquet Vaporizers?
Injection Vaporizers, only used with specialty Maquet machines tho
Which anesthetic agent would be closer downstrean to pt on the machine?
Des
-they used to be organized from most-least volatile closer to pt but not important with modern interlocking systems now
Equation for calculating liquid consumption in vaporizers:
3 X FGF X Set Conc. = consumption of liquid in mL/hr
Calculate fluid consumed if FGF is 3L/min and set conc. is 1%
3 X 3 X 1 = 9ml/hr
T/F Altitude affects all vaporizer outputs
False!
-DOES affect Desflurane Injector Vaporizers (very sensitive, needs recalibration in high altitudes)
-DOES NOT affect variable bypass vaporizers (uses PARTIAL PRESSURE)
Calculate fluid consumed if FGF is 2L/min and set conc. is 1.5%
3 X 2 X 1.5 = 9ml/hr
The pumping effect in vaporizer creates:
A. Normal vaporizer function
B. Momentary backpressure from ventilation resulting in retrograde vapor flow
C. Prolonged back pressure from the outlet into the bypass flow
D. Vaporizer leak resulting in underdosing of patient
B
A modern example of an open circuit breathing circuit would be:
Nasal Cannula
Classifications of Breathing Circuits: (4)
-open
-semi-open
-semi-closed
-closed
4 main parts of the Semi-Open Mapleson breathing Circuit:
-Resevoir Bag
-APL Valve
-Fresh Gas Inlet
-Corrugated Tube
Reservoir bags are _ in shape, made of rubber or plastic and come in a _ L size for adults and < _L for peds
ellispoidal shape
2L size for adults, <0.5L size for peds
What is an APL valve and what are its other names?
Adjustable Pressure Limiting Valve
-Expiratory Valve
-Pop Off Valve
-Pressure Relief Valve
-Spill Valve
—helps control pressure in breathing circuit (open for spont. pts and semiclosed or closed in AC/ vent pts)
The corrugated tube on breathing circuits is made of plastic, silicon, or rubber and has 3 main functions:
-Increase flexibility of circuit
-Prevent kinks in tube
-Provides added turbulent flow to mix the anesthetic agent
Which Mapleson circuit would be best suited for a pt who is spontaneously breathing?
Mapleson A / Magill
A<D<B
Mapleson Circuits are classified based on:
positions of APL valve, fresh gas inlet/flow, and reservoir bag
Why is Mapleson A the best choice for spont. breathing pts?
Can produce a Mv of 80mL/kg/min, requires over 3x more Mv or FGF than others during controlled vent
Where is everything on the Mapleson A circuit?
APL valve: at pt end
FGF and reservoir bag at end of AGM
The ideal Mapleson circuit for a vented pt would be:
Mapleson D / Bain Circuit
D>B>A
Why is Mapleson D ideal for vented pts?
-controlled about 1-2X pt’s Mv
-has a COAXIAL circuit (tubs inside tube) and has inspiratory and expiratory tube, less efficient for spont. breathing pts (2-3x pts Mv)
Where is everything on the MApleson D circuit?
-FGF is DISTAL to APL and close to mask
-APL and bag are farther away
-inner tube is FGF and outer tube is expiratory
Necessary components for circle circuit:
-CO2 absorber
-one way valves (insp + exp.)
T/F There is no rebreathing in circle circuit because of one way valves/co2 absorber
False
There is dead space in Y site of I+E part of tubes where pt can rebreathe CO2
A pt’s last possible defense of a hypoxic mix is the _ _ _ and is found on the _ _.
Oxygen Analyzer Device; inspiratory limb
-will monitor O2 and alarm if low
T/F The APL valve controls pressure in circuit during mechanical venilation
False- SV or manual breathing only
Reservoir bag helps with _ pt and APL valve helps with _ _.
venting pt, generating pressure
Respirometer:
measures volume of each breath
PEEP valve is found in the _ _
Circle Circuit NOT VENTILATOR
PEEP adds resistance to _.
expiration
Which type of circuits REQUIRE CO2 Absorbers?
Semi-closed and Closed
During inspiration the spill valve _ to ensure volume is delivered and _ _ compresses bellows
CLOSES , driving gas
During Expiration driving gas flow _ and _ gas fills the bellows
stops
exhaled gas
T/F Gas in bellows when rising during expiration= exhaled Vt
False, Exhaled Vt AND FGF during exhalation
Ascending bellows rise with _ and will not fill if system is disconnected (safer)
EXPIRATION not inspiration
Descending bellows _ with expiration AND gravity
fall
Bellow types are named after their action during _.
Expiration!
ex) ascending bellows rise on expirarion
Which way do you turn APL valve to OPEN it?
counterclockwise
Diff between gas + vapor
Gas is gaseous form of substance that is gas at room temp, a vapor is the gaseous form of a LIQUID at room temp
Piston Vents mechanism:
use electricity, not O2 as driving gas to function, allow for greater Vt accuracy
Piston vents safety feature:
+ and - relief valves
-prevent - opens if pressure insult -8cmH2O)
-+ relief valves open if system pressure > 75cmH2O
In which type of ventilator can you see reservoir bag inflate / deflate with expiration?
Piston Vents
-if collapsed there is a problem
Decoupling occurs with _ and _, this feature is found on _ vents.
Vt and FGF, new vents
Decoupling AGMs adjust to reduce the risk of _ and ensure the set _ is what pt receives.
barotrauma, Vt
Coupled AGMs couples _ and _, and this feature is found on _ vents.
Vt and FGF, old vents
Coupling of Vt and FGF could result in: (3 things)
-barotrauma
-errors in Vt and Vm
-losing volume to compliance
In vents that couple Vt and FGF: how is total Vt measured?
Total Vt = Vt on vent + FGF during insp. - volume lost in compliance
T/F Attaching something(extra tubing, etc.) to Y piece will increase dead space.
True
APL valve is found _ the expiratory unidirectional valve.
AFTER
T/F APL valve is the Pop off Valve
true
You are watching your reservoir bag slowly stop inflating and deflating and you realize your pt stopped breathing, use the _ _ which is a stopcock to switch flow from bag/ APL to the vent.
Selector Switch!
3 Main Alarms on Breathing Circuit:
-Low Peak Airway Pressure
-High Peak Airway Pressure
-Sustained Airway Pressure
PEEP can be introduced to pt during:
-spont. breathing, bagging a pt, and mech vent
In Semi Open breathing circuits, FGF is _ than pt’s Mv
greater than
-ex) 10L/min at induction
In Semi Closed breathing circuits, FGF is _ than pt’s Mv
less than
-ex) 2L/min during maintenance phase
Traditional open circuit=
Mapleson circuits
Which 2 are not part of Mapleson circuit but part of the circle circuit?
Mask
Apl
Unidirectional valves
Corrugated tubing
Co2 absorber
Reservoir bag
Fresh gas inlet
unidirectional valves, CO2 absorbers
Intrinsic PEEP in regards to vents occurs when:
after circuit pressure exceeds 3cmH20 (or whatever you set) and vent spill valve opens, letting extra gas out to scavenging system
Which type of CO2 absorber risks CO or compound A formation?
Soda Lime bc of its strong bases
Benefit of Soda Lime CO2 Absorber:
-cheap
-Absorbs 14-23L CO2 per 100g of absorbent
Benefit of Calcium Hydroxide as CO2 Absorber
-far less risk of CO and compound A formation
Granules of CO2 absorber are measured in mesh sizes and are optimally
4-8mesh
-size creates balance in surface area of absorption ability and airflow resistance
CO2 absorbers will turn purple from Ethyl Violet dye and this indicates:
need to be changed, no longer absorbing much CO2
CO2 absorbers stop working in 2 conditions:
-exhausted (~pH10.3)
-desiccated (too dry)
Which anesthetic agent poses the greatest risk at creating compound A in the CO2 absorbers?
Sevoflurane
Active Scavenging systems rely on
-suction/evac unit
-negative pressure relief
-positive pressure relief so no barotrauma to pt
Which type of scavenging system can be open or closed?
Active
Passive Scavenging Systems rely on
-passive flow of gas from upstream
-don’t risk negative pressure insults
-have high pressure relief
Which type of scavenging system can only be closed?
Passive
ORs cannot have any higher exposures than: _ ppm of N2O, _ppm of volatile agents, and no more than _ppm if using halogen agent and N2O together
25ppm of N2O
2ppm of Agent
0.5ppm of Halogen + N2O
What part of the bypass vaporizer is this?
Anesthetic Agent
What part of the bypass vaporizer is this?
Concentrating Cone
What part of the bypass vaporizer is this?
Pressure Compensator
What part of the bypass vaporizer is this?
Temperature-compensating Bypass
What part of the bypass vaporizer is this?
Vaporizing Chamber
What part of the bypass vaporizer is this?
Wick
Which kind of Mapleson Circuit is this and does it function better with a vented pt or one spontaneously breathing?
A, spontaneously breathing
Which kind of Mapleson Circuit is this and does it function better with a vented pt or one spontaneously breathing?
D, vented pt
A vent leak could indicate or cause:
-a crack somewhere
-gas mixing from drive gas and circuit
-increased FiO2
-barotrauma
-dilution
If low pressure alarm ringing in breathing circuit could be caused by:
-circuit disconnect * most common cause- usually at Y piece between ETT+circuit
-CO2 Absorber having a poor seal
-Moisture in Vent
-malfunctioning bag/vent selector switch
Assess these when low pressure alarm on breathing circuit rings:
-monitor pt chest rise
-EtCO2 and any changes in Vt
-assess integrity of breathing circuit
-check if ascending bellows are not rising
-check if bag is deflated with piston vent
If high pressure alarm ringing in breathing circuit could be caused by:
-malfunctioning unidirectional valves-most common
-consider pt having bronchospasm always check pt 1st
-ETT occlusion
-PEEP valve occlusion
-plastic covering from CO2 absorber or mask occluding something
-scavenging malfunction
-vent spill valve issue
What does this represent on capnograph?
Alpha Angle (measures obstruction~100-110*)
What does this represent on capnograph?
Alveolar Plateau (where magic gas exchange happens)
What does this represent on capnograph?
Beta Angle (~90* measures rebreathing)
What does this represent on capnograph?
Anatomic Dead Space
What does this represent on capnograph?
Dead Space Transitioning to alveolar plateau
What does this represent on capnograph?
Inhalation of gas
T/F A capnograph of someone with severe COPD, bronchospasm, or ETT kink will not reach plateau before next inspiration.
true
T/F There is an alarm for when CO2 absorbers are exhausted.
False we must NOTICE it!
Reduce the risk of CO poisoning by:
-changing CO2 absorbers
-use minimum FGF rate of 1-2L/min after 2 MAC hrs can increase
CO poisoning shifts the oxyhemoglobin curve to the _.
left; reduces pt’s O2 carrying capacity
What does this curve show?
normal capnograph with 3 phases
What does this curve show?
Obstruction-no plateau
-COPD
-Bronchospasm
-Kinked ETT
What does this curve show?
Curare Cleft - spontaneous respiratory effort
-great if waking up, not great if we want deep
What does this curve show?
Failure of CO2 to return to 0
-bad expiratory valve
-CO2 absorber is exhausted
What does this curve show?
Persistent exhaled gas during inspiratory cycle
-bad inspiratory valve
What does this curve show?
Cardiac Oscillations with heart beating against lungs
What does this curve show?
Shark fin= obstruction
-bronchospasm
-COPD
-Asthma
What does this curve show?
Hyperventilation
What does this curve show?
Hypoventilation
Where do we measure EtCO2 on curve?
top of beta angle
Ways to improve SpO2 signal:
-wrapping finger and probe in foil from alcohol pad
-warming extremity
-digit block
-vasodilating cream
-give IV arterial vasodilator
Things that cause SpO2 artifact:
-moving
-hypothermia
-hypovolemia
-shock
-poor placement
-nail polish
-fake nails
Methylene Blue can interfere with SpO2 signal for up to _ minutes
5
Carboyhemoglobinemia can cause falsely _ SpO2
high
Methemoglobinemia will cause SpO2 to stay around _ %
85%
T/F SpO2 is a good indicator for successful intubation
False, pt sats can stay elevated after intubation for a little due to hyperoxygenation
In pulse oximetry, the red light is absorbed _ by deO2 hemoglobin than by O2ed hemoglobin
more
In pulse oximetry, the INFRAred light is absorbed _ by deO2 hemoglobin than by O2ed hemoglobin
less
Things that cause a shift left on oxyhgb dissociation curve (Hgb hangs onto O2 more-less affinity for tissues):
-low CO2
-high blood pH/ low H+ ions
-hypothermia
Things that cause a shift right on oxyhgb dissociation curve (Hgb lets go of O2 more-higher affinity to tissue):
-low blood pH/ excess H+ ions
-hyperthermia
-high CO2
Different causes of low lung perfusion that result in more dead space, diluted exhaled CO2 and low EtCO2: (3 items)
-air embolism
-low CO
-low BP
The gradient between PaCO2 and EtCO2 (2-5mmHg) reflects
alveolar dead space
MH causes EtCO2 to rise because of
increased metabolic rate
A sudden loss of CO2 during expiration indicates
disconnection
EtCO2 cannot detect what kind of intubation?
mainstem bronchial
EtCO2 quickly detects what kind of intubation
esophageal
T/F anywhere you place a SpO2 probe that picks up a good waveform and reading is fair game
true
Fastest measurement locations of SpO2:
ear, nose, tongue, forehead, esophagus
Slowest measurement location of SpO2
toe
2 Ways to collect CO2 analysis measurement:
-from within anesthesia circuit (mainstream or non-diverting)
-from circuit and measured inside monitor component using infrared radiation (side stream or diverting)
Pros of measuring CO2 via anesthesia circuit(mainstream):
-real time CO2 level at insp and exp
-faster response
-measures CO2 at sample site
-used in ICU
-no water trap
Cons of measuring CO2 via anesthesia circuit (mainstream):
-only measures CO2- not anesthetic agents
-increases dead space
-electronics are vulnerable to damage
- heavy/bulky
Pros of measuring CO2 via monitor component with infrared(sidestream):
-measures CO2 and anesthetic gases
-used in AGM
-device is out of airway
-can be used on non-intubated pts
-can analyze mult gases
Cons of measuring CO2 via monitor component with infrared (sidestream):
-diverts sample off Y piece
-needs scavenging
-measures farther from sample site
-pulls gas from circuit 150-200ml/min-slow
-needs water trap, accumulates condensation
During a general anesthetic, you are unable to ventilate a patient due to low pressure in the system. What is the best course of action?
-switch to ambubag/ bag-mask vent and convert to TIVA
With Nitrous Oxide, as long as liquid remains in the cylinder, the partial pressure measured by the bourdon pressure gauge will read _ psi
745PSI
Regarding savaging systems- removal of too much gas would create _pressure in the circuit, while removal of too little gas may increase the risk of _ (excess + pressure) .
negative pressure, barotrauma
Most fragile part of AGM
flowmeter glass tubes
When installing E Cylinder look for:
-cracked cylinder
-damage
-ensure only one washer
-PISS pins
-ensure no audible leak
-ensure good pressure reading
Under which conditions will hypoxic guard fail?
- Wrong gas in wrong canister (aka not administering N2O)
- Leak downstream of flowmeter
- Pneumatic/mechanical failure (hypoxic guard breaking)
- Administration of third gas (helium)
How can you supplement the hypoxic guard to prevent failure?
Use of an oxygen analyzer
What property should material have to help control temperature for vaporizers?
High heat conductivity
What is the minimum FGF for a non-breathing circuit?
5L/min
What determines the rebreathing amount for non-breathing systems?
FGF rate
When to change CO2 granules (optimally)
Unless they’re exhausted during a case,
between cases. Changing granules reportedly causes hypoventilation.
When to avoid low FGF?
Malignant hyperthermia, smoke inhalation, other situations in which you’d want to wash out gas
Atmospheric Pressure is
760 mmHg or 14.7 PSI
