Machine Flashcards
What are some components of an anesthesia workstation?
Battery backup
alarms
monitors
flowmeters
oxygen flush valve
vaporizers
pipeline gas supply
e-cylinder
Fail-safe valve
-purpose
-trigger
ensure that whenever oxygen pressure is reduced and until flow ceases the set oxygen concentration will not decrease in the common gas outlet.
loss of oxygen pressure triggers the high-priority alarm audible and visible (around 30 psi)
Can a hypoxic mixture be delivered from the anesthesia machine with an intact fail-safe valve?
Yes
as long as there is pressure in the oxygen line nothing in the fail-safe system prevents you from turning on a mixture of 100% nitrous oxide
pipeline crossover
How are oxygen, nitrous oxide, and air gases that are used in anesthesia typically delivered to the anesthesia machine?
via pipeline system or gas cylinders
At what pressure must gases be delivered for proper function of the anesthesia machine?
Pipeline = 50 psi
Cylinder
oxygen and air = 1900 psig
nitrous = 745 psig
Oxygen must remain 25 psi or greater!
How is the delivery of erroneous gases to the anesthesia machine minimized?
- Color-coded pipes/cylinders.
- Diameter Index Safety System (DISS).
- Safety system on pipeline systems to prevent improper connection of supply hoses. (does not prevent hypoxic gas mixture to patient)
- PISS for cylinders
What is the purpose of the cylinders of oxygen and nitrous oxide that are found on the back of the anesthesia machine?
in case of pipeline failure
How is an erroneous hookup of a gas cylinder to the anesthesia machine minimized?
Pin index safety system PISS
(oxygen pin 2&5, air pin 1&5, nitrous pin 3&5)
Oxygen PISS
2 & 5
Nitrous Oxide PISS
3 & 5
Air PISS
1 & 5
Oxygen Cylinder:
color
state
capacity
PSI when full
green
gas
660 L
1900 psi
Nitrous Oxide Cylinder:
color
state
capacity
PSI when full
blue
liquid
1590 L
745 psi
Carbon Dioxide Cylinder:
color
state
capacity
PSI when full
Gray
liquid
6900 L
2200 psi
Air Cylinder:
color
state
capacity
PSI when full
Yellow
gas
625 L
1900 psi
How is the pressure of oxygen related to the volume of oxygen in its cylinder? What does this mean when calculating the volume of remaining oxygen?
Pressure drops as oxygen volume drops.
Tank capacity (L)/ full tank pressure (psi) x L remaining/current psi. Cross multiply and divide by 1900 = L left in tank
Note: tank capacity is 660 L; full tank pressure is 1900 psi
How is the pressure of nitrous oxide related to the volume of nitrous oxide in its cylinder?
-Pressure is 745 psig until about 400 L remaining
-liquified gas
-pressure depends on the liquid’s vapor pressure; does not indicate the amount of gas remaining
PRESSURE < 745 psi —> REPLACE TANK
Why does atmospheric water vapor accumulate as frost on the outside surface of oxygen tanks and nitrous oxide tanks in use?
The can gets cold when sudden release of gas as pressure decreases.
It tries to gain energy (heat) back from the environment.
Potential to cause frostbite. (more likely to occur in humid locations) Joule Thomson Effect
Flowmeters
show the flow rate of gas being administered
precisely controls and measures gas flow to common gas outlet
How do flowmeters work?
Flow rate depends on:
viscosity at low flow levels
density at high flow rates
This drives the bobbin (indicator ball)
Thorpe tube is tapered (narrow at bottom, widens towards the top); as flow increases, marker rises toward wider part, greater flows pass around it, and reach the common gas outlet.
Upper part (wide) has to do with density (high flow)
Lower part (narrow) has to do with viscosity (low flow)
T/F
flowmeters for various gases interchangeable
false
specifically designed and calibrated for each gas
Why is the oxygen flowmeter the last flowmeter in a series on the anesthesia machine with respect to the direction in which the gas flows?
To prevent a hypoxic mixture
oxygen is the last gas to leave the machine and is closest to the common gas outlet. All gasses flow to the right; oxygen is furthest on the right.
Who decides if gas is pure enough to be medical grade?
FDA
Who is responsible for marking and labeling medical gas cylinders?
dept of transportation
DOT
-manufacturing
-marking/labeling
-storage
-filling
-transportation/handling
-disposition
Regulate matters affecting gases
the safety and health of employees
DOL & OSHA
Which gases are liquified?
N2O only (apply 25-1500 psi)
liquid at room T
T/F
The NFPA standards regarding oxidation and combustion of medical gases are optional
True
Non-liquefied gas
does not liquify at room T regardless of pressure applied
O2
helium
air
nitrogen
T/F
Liquid O2 is not used in hospitals
False
hospital supply is usually liquid
the cylinder we use in patient care are gas
What safety system is built into gas cylinders? What’s it for?
PISS
decrease chance of misconnection of gases & delivering hypoxic mixture
When going to MRI, use a (3AA/3AL) cylinder.
3AL (aluminum)
MRI compatible
“AL go with you to MRI”
Or
“Bring 3AA to MRI, you’ll be screaming AA”
____ metal is not compatible with MRI.
ferrous
A cylinder has a label on it saying 3AA. This means…
it’s a steel cylinder
do not use in MRI
“MRI machines steal steel cylinders”
When gas exits the cylinder, it passes thru a ____ on the neck of the cylinder which works to….
valve; pressure-regulator
drops pressure to workable amount
T/F
Cylinders attach to the back of the anesthesia machine via the pressure relief valve.
False
yoke screw depression
What part of the anesthesia machine drops pressure from the cylinder to a workable pressure?
first stage regulator 1900 psi to more usable psi
A cylinder will explode at temps over…
134 F
57 C
Which size cylinder is most commonly used in anesthesia?
E
As CRNAs, WE use E
Gay-Lussac’s Law
the pressure of a gas increases as its temperature increases, assuming constant mass
and volume
P1/T1 = P2/T2
T/F
We can use the pressure reading on a N2O cylinder to tell us how much is left in the tank.
false
must weigh and compare to full
the pressure will remain constant until all liquid is gone
replace tank when pressure drops
Who is she?
first stage regulator
Critical temp for N2O
36 C
Joule Thomson Effect
- Highly compressed gas is suddenly released
- Cooling or freezing effect on the surface of the cylinder
- Potential for thermal injury, specifically for nitrous oxide
PSI for pipeline
50-55 psi
Benefits of liquid O2
store more in same amount of space
less risk of igniting
cost effective
The DISS functions to…
Prevents improper connection of supply hoses
T/F
The DISS prevents administration of a hypoxic gas mixture.
FALSE
if there’s a pipeline crossover, can still give hypox mixture
The only monitor that can detect low O2 concentrations
Oxygen monitor
Where is the oxygen monitor located?
Located distal to the common gas outlet, as proximal to the patient as possible to be
able to determine the concentration of oxygen moving towards the patient
Emergency equipment
Ambu (check for mask & all needed connections)
O2
Suction
for sim: add extra circuit
High pressure system
PSI
components
1900 psi —> 45 psi at first stage regulator
Hanger yoke
hanger yoke check valve
cylinder pressure regulator
cylinder pressure gauge
Intermediate Pressure System
PSI
components
30 - 55 psi
Starts at the first stage regulator (when using cylinder)
-pipeline gas inlets & pressure gauges (deliver at ~50 psi)
-Second-stage pressure regulator (drops to 15-30 psi; safe pressure for pt)
-ventilator power outlet accessory
-O2 flush valve
-supply failure alarm system
-second stage pressure regulator
-flowmeter valves
Low Pressure System
PSI
components
*15 to 30 psi
- Begins at second stage regulator (all gas now ~16 psi)
- Components distal to the flowmeter needle:
-Flowmeter tubes
-vaporizers
-temperature compensating bypass valve
-common gas outlet
When should we NOT use the O2 flush valve? Why?
Never use O2 flush valve when connected to pt
barotrauma
The O2 flush valve delivers gas at ____ L/min. Its best used for….
35-75 L/min
refill/flush breathing circuit rapidly
Oxygen Failure Safety Valve
Shuts off the flow of all other gases when O2 pressure drops below a set limit (20 – 25 psi)
PPT: below 28 psi
Does the Oxygen Failure Safety Valve prevent administration of a hypoxic mixture?
Noooo
What ensures that N2O can only be delivered in the presence of oxygen?
Oxygen Proportioning Device
What is the safety proportioning ratio of N2O and O2?
N2O:O2
3:1
Chain-Link Proportioning Device
How many teeth on the dials?
N2O = 14
O2 = 28
The ___ knob is fluted and protrudes further out.
Oxygen
(US machines)
Oxygen is positioned which way for safety?
farthest to the right
always last gas to leave
Flowmeters
Use a ___ that displays the flow of gas thru a ___ tube
Bobbin (indicator)
Thorpe tube
T/F
Flowmeters for all gases are identical.
False
calibrated for each gas
At high turbulent flow, the flowmeter depends on the gas’s ____. At low laminar flow, it depends on ____.
high turb flow = density
low lam flow = viscosity
____ is the dominant factor in determining gas flow.
density of the gas
Thorpe tubes are wider at the (bottom/top)
top
allows greater gas flow
Considerations when using floweters
Leaks/cracks (hypoxic gas mixtr)
-this is why O2 is last oxygen to leave
Malfxn (dirt inside, misaligned, sticking)
Volatile agent
anesthetic agent which exists as a liquid at room temp and evaporates easily for administration by inhalation
Heat of vaporization
is the number of calories required at a specific temperature to convert 1 Gram of liquid to vapor
Vaporizers reside outside the breathing circuit until…
they’re turned on
Vaporizers must not be tilted beyond ___ degrees or else…
45
must empty completely
can deliver uncertain % of drug
Vaporizers are calibrated to be ____ compensated.
temperature
Ensures only one vaporizer is turned on
vaporizer interlock
Common Gas Outlet
Where gas mixtures from flow meters enter the breathing circuit
Where does gas from the common gas outlet enter the breathing circuit?
Fresh gas inlet
Which volatile agent is heated? Why?
Desflurane
-high vapor pressure (decreased intermolecular attraction)
-needs heated, pressurized vaporizer to deliver a regulated concentration
-container increases vapor pressure, but once opened to air, the desflurane would quickly boil away (BP close to room temp)
Modern vaporizers are ___ specific.
agent
Which vaporizer do we use for desflurane?
TEC 6
APL Valve
allows gases to exit the breathing system
- Adjustable pressure level valve
- Pop off valve
When do we close the APL valve? What value do we turn the valve to?
70 = closed
When is the APL valve open?
spontaneous ventilation (prevents pressure buildup; allows expired gases to exit system)
manual or assisted bag ventilation
open = 0
When is the APL valve partially closed?
limits gas exiting the system
closed = 70
What happens if the APL is open too wide?
too much volume escapes
not enough delivered to the patient
What happens if the APL valve is closed too tightly?
not enough volume escapes
larger volumes/ high airway pressures
Unidirectional Valves
- Maintains flow of anesthetic gas in the direction intended
*inspiratory limb: forward flow of gas to patient
*expiratory limb: moves gas patient –> bag/ventilator & scavenger system
What happens if the unidirectional valves malfunction?
rebreathing of CO2 may occur
Carbon Dioxide Absorbent
- Allows rebreathing of alveolar gas (conserves heat and moisture)
- removes CO2
- Economical rebreathing of low flow gases and anesthetic agents
- Soda Lime or Amsorb (Baralyme d/c’d)
Carbon Dioxide Absorbent
end products?
heat, water, and calcium carbonate
Carbon Dioxide Absorbent
sizing?
4-8 mesh granules
CO2 neutralization produces…
carbonates, water, and heat
When to replace CO2 absorber
50-70% of granules are purple
CO2 absorber will turn ____ due to the indicator dye called ____ as the ____ concentration increases.
blue/purple color
Indicator dye (ethyl violet)
hydrogen ion
At the start of workday, soda lime should be ____. After use it will be ___.
cold
warm
____ can interact w strong bases in soda lime to produce the toxic product, ____.
Sevoflurane
Compound A
Compound A formation is most common with with CO absorber brand?
Baralyme
“A comes from B”
“Good bye Baralyme!”
Higher risk of forming Compound A
High absorbent temperatures
total gas flow less than 1L/min
drying of absorbent
length of anesthetic may increase risk
____, ___, & ___ combines with CO2 absorbent and may produce carbon monoxide.
Desflurane, isoflurane & enflurane
Carbon monox = D.I.E.
Higher risk of forming carbon monoxide
baralyme
high temp in absorber
dry absorbent
high concentrations
increased length of time
HME benefits
economical way of adding moisture to inhaled gases
HME function
trapping the moisture in exhaled gases
conserve heat using same method
can be active or passive humidifier
Example of a passive humidifier
HME
Anesthesia machine ventilators
- Turn the bag/ vent switch to the ventilator mode; bypasses breathing bag & APL; bellows replace their function
T/F
Descending bellows are safer for use, so they are more common.
False
Ascending bellows are safer
if a leak is present, the bellow will not ascend, versus descending which will move normally even if there’s a leak
Ascending bellows (rise/fall) as patient exhales.
rise
What is the driving gas for bellow movement?
Oxygen or air
Tidal volume
volume of gas entering or leaving the patient during the inspiratory or expiratory phase time
Minute volume
sum of the tidal volumes in one minute
Ventilatory Frequency
number of respiratory cycles per minute
Inspiratory flow Time
the period between the beginning and end of inspiratory flow
Inspiratory phase time
period of time between the start of inspiratory flow and the beginning of expiratory flow
or sum of the inspiratory flow time and the
inspiratory pause time
Expiratory flow time
time between the beginning and end of expiratory flow
Expiratory pause time
interval from the end of expiratory flow to the start of inspiratory flow
Expiratory phase time
time between the start of expiratory flow and the start of inspiratory flow
or
the sum of the expiratory flow time and the expiratory pause time
I: E ratio
- The ratio of inspiratory phase time to expiratory phase time.
- 1: 2 ratio
A COPD patient may need (shorter/longer) expiratory phase time.
longer
Resistance
pressure difference per unit flow across the airway
usually increases as flow increases
Compliance
ratio of a change in volume to a change in pressure
Tidal Volume
- 5-8 mL/kg of ideal body weight is generally indicated
- Barotrauma and volutrauma in higher volumes
- Plateau pressure less than 35 cm H2O
Respiratory Rate
normal range
what if it’s too high?
- Adult RR= 8-12 breaths per minute
- High RR- less time for exhalation, increases mean airway pressure, air trapping in
patients with COPD
What is the goal when deciding resp rate?
keep ETCO2 between 35 and 45 mmHg
Supplemental O2 should be the lowest FiO2 that produces SaO2 greater than ___ & and PaO2 of greater than ____.
90%
60
During induction/emergence, give ____ FiO2.
100%
During the case, how much FiO2 is recommended?
50-60%
Physiologic PEEP
value
benefits
3-5 cm H2O
reduces the risk of atelectasis, trauma, minimizes V/Q mismatches
common to prevent FRC decreases in normal lungs
What vent mode is used a paralyzed or apneic pt?
Continuous mandatory ventilation (CMV)
Suggested Vent Settings
- RR= 10 (8-12 for adults)
- TV= 500 (5-8 mL/kg ideal body weight)
- I:E Ratio= 1:2
- PS= 10
- PEEP= 5
Scavenger System
removes waste anesthetic gases via breathing circuit thru APL valve or the ventilator spill valve and out of the OR
⭐️
NIOSH Maximum Allowable WAG Limits
- 25 ppm N2O used w O2
- 2 ppm halogen agent w O2
- 0.5 ppm anesthetic agent is used in the presence of N2O
Passive Scavenging
- waste gases enters a passive pipeline
- carries to a vent stack
*gases exit at whatever rate they are entering the
system
Active Scavenging
- Exiting via vacuum system
- go from the breathing circuit to the hospital’s vacuum system
Closed Interface
- Needle valve to adjust exit to system, bag to allow room for overflow
Open Interface
- Allow movement of waste anesthesia gases into the environment, should be active!
Anesthesia Machine Checkout
how often do we perform?
every morning prior to the first case
Why do volatile anesthetics require placement in a vaporizer for their inhaled delivery to patients via the anesthesia machine?
To convert them from liquid to vapor.
What is the heat of vaporization?
The number of calories required at a specific temperature to convert 1 Gram of liquid to a vapor
What is vapor pressure? What influence does temperature have on vapor pressure?
The pressure exerted by the gas in equilibrium in a closed container at a given temperature. As temperature increases, more molecules enter vapor phase and vapor pressure increases
⭐️
Why are contemporary vaporizers unsuitable for use with desflurane?
Desflurane has a high vapor pressure; 3-4x higher than other inhaled anesthetics
it must be pressurized
contemporary vaporizers for volatile anesthetics are classified based on…
their vapor pressure (high vapor pressure or lower vapor pressure)
What does the term agent-specific refer to?
Agent = Volatile anesthetic gas. Each vaporizer is pressure/temperature calibrated for that specific agent.
variable-bypass
method for regulating the anesthetic agent concentration output from the vaporizer
- fresh gas from the machine flowmeters enters the vaporizer inlet
- concentration control dial determines the ratio of incoming gas that flows through the bypass chamber to that entering the vaporizing chamber (sump).
- The gas channeled through the vaporizing chamber flows over a wick system saturated with the liquid anesthetic and subsequently also becomes saturated with vapor
Flow-over
method of vaporization in contrast to a bubble-through system
T/F
The circle system is part of the low pressure system.
False
its not part of the hi, intermed, or low pressure system
Desflurane is pressurized to ___.
2 atm
⭐️
The Tec 6 Vaporizer
used for desflurane
pressurizes and heats (39 C)
blends fresh gas with des vapor
very different from variable bypass
Upon machine check, which vaporizer should be warm to the touch?
Desflurane
Desflurane got dat heat
Mechanism of variable bypass vaporizer
⭐️
Vapor pressure of desflurane
669 mmHg @ 20C (room temp)
almost 1 atm @ sea level
T/F
Even when the O2 flowmeter is off, O2 is still delivered.
True
minimum 50-150 ml/min constant flow
⭐️
Where does the low pressure system begin? Whats the psi?
at the second stage regulator
pressure now reduced to 16 psi
flowmeters, vaporizers, common gas outlet
What does the term temperature-compensated refer to? Between what temperatures is vaporizer output reliably constant?
Maintains constant vapor concentration output for given concentration dial setting, regardless of temperature
Higher temps: more gas flow through bypass chamber; less flow through vaporizing chamber
Lower temps: less flow through bypass chamber; more flow through vaporizing chamber
⭐️
out of circuit
Physically located outside of the breathing circuit.
Vaporizers are not part of the breathing circuit when they are off
How does tipping of a vaporizer affect vaporizer output?
caution: incorrectly “switched out” or moved.
Excessive tipping: liquid agent can enter bypass chamber–> output with extremely high agent vapor concentration
How is the delivery of two different volatile anesthetics to the same patient via the same anesthesia machine prevented?
Vaporizer Interlock Mechanism
How is the potential risk of filling the agent-specific vaporizer with the erroneous volatile anesthetic minimized?
The agent-specific fill devices
Certain fill adapters per agent
What is the function of anesthetic breathing systems?
Deliver oxygen & anesthetic mixture
eliminate CO2 from the breathing circuit
How do anesthetic breathing systems impart resistance to the spontaneously ventilating patient?
Increase resistance:
Small diameter or long circuits
small ET tubes
LMAs
HMEs
unidirectional valves
Controlled vent modes when pt is trying to spont breathe
What are some features of an anesthetic breathing system that enable them to be classified as either open, semi-open, closed, or semi-closed?
Open= no reservoir and no rebreathing.
semi-open= has reservoir but no rebreathing.
semi-closed= has reservoir and partial rebreathing.
closed= has reservoir and complete rebreathing.
most commonly used anesthetic breathing systems?
Circle breathing systems
How does the circle system prevent rebreathing of carbon dioxide?
Unidirectional valves and CO2 absorbents
What are the classifications of a circle system and on what does this depend?
Semiopen: no rebreathing and requires very high FGF
Semiclosed: some rebreathing of exhaled gases
Closed: FGF exactly matches that being taken up or consumed by the patient; complete rebreathing of exhaled gases after absorption of CO2; overflow (APL) valve or ventilator pressure relief valve remains closed
most commonly used circle breathing system used in the United States?
Semiclosed system
advantages of the semi-closed and closed circle systems?
They conserve heat and moisture efficiently.
Economic use of anesthetic gases.
Minimizes release of anesthetic gases into environment.
disadvantages of the circle anesthetic breathing system?
Complex design (10+ different connections)
Malfunction of unidirectional valves can result in life-threatening problems. (rebreathe CO2, increased resistance)
Rebreathing, total occlusion of circuit if stuck shut.
components of a circle system
Fresh gas inflow
unidirectional valves
corrugated tubes
APL valve
Y-piece
reservoir bag
CO2 Absorbent
oxygen sensor
Where is the dead space in the circle system?
From the y piece to the patients lungs, including ETT, connectors, and valves
Pros and cons of the corrugated tubing in the circle system?
Pros:
Prevents kinking of the tube
sturdy but flexible
Cons:
During positive-pressure ventilation, some of the delivered gas distends the corrugated tubing and some is compressed within the circuit, which leads to a smaller delivered tidal volume
Y-piece connector
connects to ETT or mask
connects to the inspiratory limb and expiratory limb
other names for the adjustable pressure-limiting (APL) valve?
Pop-off valve or adjustable pressure relief valve
advantages of the reservoir bag on the circle system?
Prevents retrograde flow through the system
If there’s a one-way check valve on the machine, (+/-) pressure leak test is needed.
Negative
A positive-pressure leak test will not detect leaks in the LPC of a machine with an outlet check valve.
What happens if Desflurane is placed into a variable-bypass vaporizer?
hypoxic mixture
overdose of Desflurane
T/F
Tec 6 desflurane vaporizer is a variable bypass vaporizer.
False
gas-vapor blender
What is the function of anesthetic breathing systems?
deliver oxygen and anesthetic agent while eliminating CO2 to prevent rebreathing
How do anesthetic breathing systems impart resistance to the spontaneously ventilating patient?
add considerable resistance to inhalation because peak flows as high as 60 L/min are reached during spontaneous inspiration.
A non-contained system where the patient exchanges gas with the atmosphere
Open system: has no reservoir & no rebreathing
In this system, FGF is > than the pt’s minute ventilation & there is no breathing of exhaled gas
Semi-open system: has a reservoir but no breathing
This system uses a very low FGF, complete breathing of exhaled gas, gas does not exit the scavenger, APL valve is closed, and gas replaced is Pt’s O2 consumption + anesthetic gas absorbed by pt
Closed system: has a reservoir & complete rebreathing
What are the most commonly used anesthetic breathing systems?
The circle system remains the most popular breathing system in the US
How does the circle anesthetic breathing system get its name?
Components are arranged in a circular manner
How does the circle system prevent rebreathing of carbon dioxide?
CO2 absorber
What are some advantages of the semi-closed and closed circle systems?
-Maintenance of relatively stable inspired gas concentrations
-conservation of respiratory moisture & heat
-prevention of operating room atmosphere contamination by waste gases
What are some disadvantages of the circle anesthetic breathing system?
system may have 10+ different connections = high risk for misconnections, disconnections, obstructions, & leaks
What is the impact of the rebreathing of anesthetic gases in a semi-closed circle system?
Allows for rebreathing of alveolar gas which conserves heat and moisture and decreases need for higher flow of gases.
What are the components of a circle system?
Fresh gas inflow, unidirectional valves, corrugated tubing, APL valve, Y piece, Reservoir bag, CO2 absorber.
What is the purpose of unidirectional valves in the circle system?
Maintain the flow of anesthetic gas in the direction intended.
What would occur if one of the unidirectional valves should become incompetent?
If either valve is stuck, rebreathing of carbon dioxide could occur.
In unidirectional valves, Inspiratory valve is ____ during inspiration & _____ during expiration
open
closed
Where is the dead space in the circle system?
in the Y piece connected to the ETT where inspired and expired gasses meet.
What is advantageous about the corrugated tubing in the circle system?
Increased flexibility and decreased kinking.
What is disadvantageous about the corrugated tubing in the circle system?
During positive-pressure ventilation, some of the delivered gas distends the corrugated tubing and some is compressed within the circuit, which leads to a smaller delivered tidal volume
Describe the Y-piece connector in the circle system circuit.
It is used to divert inhaled and exhaled gasses from the patients lungs.
Describe the function of the APL valve when the “bag/vent” selector switch is set to “bag.”
(1) allows venting of excess gas from breathing system into the waste gas scavenging system
(2) can be adjusted to provide assisted or controlled ventilation of the pt’s lungs by manual compression of the gas reservoir bag.
What are the advantages of the reservoir bag on the circle system?
As a reservoir for anesthetic gases or oxygen
Serves as a visual assessment of the existence & rough estimate of the volume of ventilation
means for manual ventilation
What is the inflow volume of fresh gases in a closed anesthetic breathing system?
the FGF into the circle system (150 to 500 mL/min) satisfies the patient’s metabolic oxygen requirements (150 to 250 mL/min during anesthesia) and replaces anesthetic gases lost by virtue of tissue uptake
What are some advantages to the closed circle anesthetic breathing system?
Maximal humidification and warming of inhaled gases
Less pollution of the surrounding atmosphere
Economy in the use of anesthetics
What is a disadvantage to the closed circle anesthetic breathing system?
inability to rapidly change the delivered concentration of anesthetic gases and oxygen because of the low fresh gas inflow
What are the dangers of the closed circle anesthetic breathing system?
Unpredictable and possibly insufficient concentrations of oxygen
Unknown and possibly excessive concentrations of potent anesthetic gases.
Are inspired concentrations of oxygen more or less predictable when nitrous oxide is also being delivered in a closed circle anesthetic breathing system?
more likely to occur if nitrous oxide is included in the fresh gas inflow
i.e. decreased tissue uptake of nitrous oxide with time in the presence of unchanged uptake of oxygen can result in a decreased concentration of oxygen in the alveoli.
How can the potential problem of the inadequate delivery of oxygen using a closed circle anesthetic breathing system be minimized?
can be minimized by the use of an oxygen analyzer placed on the inspiratory or expiratory limb of the closed circle system
In a closed circle anesthetic breathing system, to what extent is the inhaled concentration of anesthetic dependent on the exhaled concentration of anesthetic?
The concentration of anesthetic in exhaled gases reflects tissue uptake of the anesthetic. Initially, tissue uptake is maximal, and the concentration of anesthetic in the exhaled gases is minimal.
Subsequent rebreathing of these exhaled gases dilutes the inhaled concentration of anesthetic delivered to the patient. Therefore, high inflow concentrations of anesthetic are necessary to offset maximal tissue uptake
What parts of a circle system are eliminated in anesthesia machine ventilators when the “bag/vent” selector switch is set to “vent”?
The reservoir bag
What are two different ways in which anesthesia machine ventilators are powered?
Compressed gas, electricity, or both
Describe the mechanics of a conventional anesthesia machine ventilator during inspiration.
During inspiratory phase, O2 or air is routed to ventilator casing between bellows and rigid casing.
Pressurized air or O2 entering this space forces bellows to empty contents into pt’s lungs through inspiratory limb.
This pressurized air or oxygen also causes ventilator relief valve to close, thereby preventing inspiratory anesthetic gas from escaping into the scavenging system
Why is oxygen preferred over air as the ventilator driving gas?
If there is a leak in the bellows, the fraction of inspired oxygen will be increased.
And if ventilator driven by 50 psi oxygen or air, the peak inspiratory pressure will rise.
Why are standing or ascending bellows preferred over hanging or descending bellows?
Ascending bellows are safer
It is easier to notice disconnections (bellows will collapse & not rise again)
How are inhaled gases normally humidified in awake patients breathing through their native airway?
The upper respiratory tract (especially the nose) functions as the principal heat and moisture exchanger
What effect does tracheal intubation or the use of a laryngeal mask airway have on airway humidification?
bypasses the upper airway and thus leaves the tracheobronchial mucosa the burden of heating and humidifying inspired gases
What are the negative consequences of the lack of humidification in tracheal intubation or laryngeal mask airway?
Breathing of dry and room temperature gases in intubated patients is associated with water and heat loss from the patient
What are the advantages of HME humidifiers over other types of humidifiers?
They are (1) simple and easy to use, (2) lightweight, (3) not dependent on an external power source, (4) disposable, and (5) low cost
What are the risks of heated water vaporizers and humidifiers?
can transmit nosocomial infections, cause thermal lung injury, and increase airway resistance from increased condensation.
Describe nebulizer humidifiers used for anesthesia and in the intensive care unit
Produce a mist of microdroplets of water suspended in a gaseous medium.
Not limited by the temperature of the carrier gas.
Can deliver medications to peripheral airways.
Describe operating room scavenging
the collection and subsequent removal of vented gases from the operating room.
Excess gas from the patient exits the breathing system through APL valve or Vent relief valve
In vent mode, Gas directed to inside bellows canister to scavenging system
In the operating room, what are the Occupational Safety and Health Administration (OSHA) recommendations for the maximum concentrations of nitrous oxide and volatile anesthetics in parts per million?
Nitrous oxide (with oxygen) should be ≤ 25 ppm
Halogenated agents with oxygen should be ≤ 2 ppm
Halogenated agents + nitrous oxide should be ≤ 0.5 ppm & ≤ 25 ppm, respectively
What is required to control pollution of the atmosphere with anesthetic gases?
(1) scavenging of waste anesthetic gases, (2) periodic preventive maintenance of anesthesia equipment, (3) attention to the anesthetic technique, and (4) adequate ventilation of the operating rooms.
Describe the Active type of scavenging systems used in the operating room.
Most common
Vacuum - removes the waste gases usually outside of the building
Requires a negative pressure relief valve because the pressure in the system is negative
Describe the Passive type of scavenging systems used in the operating room.
Positive pressure of fresh gas flow pushes gases
The “weight” or pressure from the heavier-than-air anesthetic gases produces flow through the system
What are the advantages of active scavenging with a waste gas receiver mounted on the side of the anesthesia machine?
Needle valve allows adjustment of vacuum flow
Needle valve that can be adjusted so the 3-L reservoir bag will be slightly inflated and appear to “breathe” with the patient
Doesn’t require a strong vacuum to operate
What are the potential hazards of scavenging systems?
obstruction can cause excessive positive pressure leading to barotrauma
Increased risk of fire –> if gas is not vented directly outside, then rooms where gas is vented to is at risk for fire
Where might be the source of a high-pressure leak of nitrous oxide?
Leak from the washer on the secondary NO2 tank.
Where might be the source of a low-pressure leak of nitrous oxide?
Flowmeter leak
What anesthetic techniques can lead to operating room pollution?
Filing vaporizers, flushing circuits and leaving gas flow/vaporizers on.
How is carbon dioxide eliminated in open and semi-open breathing systems?
Carbon dioxide is vented to room air
How is carbon dioxide eliminated in a semi-closed or closed anesthetic breathing system?
Closed systems utilize carbon dioxide absorbents allowing the circle system to exist because it removes CO2 - preventing hypercapnia
What are two types of chemicals that are used to neutralize carbon dioxide? and what products are formed? Is reaction endothermic or exothermic?
Soda lime and Amsorb Plus absorbents
Products formed: carbonates, water, and heat,
exothermic reaction
What does soda lime consist of?
80% calcium hydroxide
15% water
4% sodium hydroxide
1% potassium hydroxide (an activator).
Why is silica added to soda lime?
Silica added to provide hardness and minimize alkaline dust formation.
*Soda lime produces alkaline dust causing bronchospasm
Why is the water in the soda lime carbon dioxide absorbent canister hazardous?
makes a slurry containing NaOH & KOH in bottom of canister –> corrosive to the skin
What does Amsorb Plus consist of?
Amsorb Plus granules consist of water, calcium hydroxide, and calcium chloride.
What two factors influence the efficiency of carbon dioxide neutralization?
Mesh size and the presence of channeling in the system
How does the size of the carbon dioxide absorbent granules affect the efficiency of carbon dioxide neutralization?
a compromise between absorptive efficiency and resistance to airflow through carbon dioxide absorbent canister.
What is the optimal carbon dioxide absorbent granule size? How is this sizing system defined?
4-8 mesh granules are used
Mesh size is # of openings per linear inch in a sieve through which the granular particles can pass
*absorbent granule size = mesh size
What does channeling in the carbon dioxide absorbent granule-containing canister refer to?
exhaled gasses will bypass granules if not packed/dispersed well in container
*Channeling decreases efficiency of granules
What is the most frequent cause of channeling in the carbon dioxide absorbent granule-containing canister?
results from loose packing of absorbent granules and can be minimized by gently shaking the canister before use.
Why do the carbon dioxide absorbent granules change color?
Contains Ethyl violet a pH-sensitive indicator dye Changes color when CO2 granules are exhausted
*changes from colorless to purple
Define carbon dioxide absorbent absorptive capacity.
determined by the maximum amount of carbon dioxide that can be absorbed by 100 g of carbon dioxide absorbent
Describe the degradation of inhaled anesthetics by soda lime to compound A
Degrades sevoflurane and halothane to unsaturated nephrotoxic compounds (compound A).
Does Amsorb Plus degrade inhaled anesthetics?
No
What factor contributes to the degradation of inhaled anesthetics by soda lime?
Total gas flow rates below 1 L/min
use of Baralyme rather than soda lime
High absorbent temperatures
High concentration of sevoflurane
Drying of CO2 absorbent (fresh sodalime + machine left on all night)
Length of anesthetic
Why do most instances of increased blood concentrations of carboxyhemoglobin occur in anesthetized patients on Monday?
occur in pt’s anesthetized on a Monday after continuous flow of O2 (flowmeter accidentally left on) through the CO2 absorbent over the weekend
What causes the development of fire and extreme heat in the breathing system?
Desiccation of the CO2 absorbent Baralyme (no longer clinically available) can lead to fire with sevoflurane use.
How often should these checkout procedures be performed?
Daily, prior to the first case
If machine is moved or vaporizers are changed new checkout must be performed
An abbreviated checkout procedure should be performed before each subsequent case
What are the most important preoperative checks?
Bag-valve mask
Functioning suction equipment
Full backup oxygen source
Machine plugged into red outlet
Backup circuit w/ mask
Why is calibration of the oxygen monitor so important?
The only machine safety device that detects problems downstream from the flowmeters
*The other machine safety devices (the fail-safe valve, the oxygen supply failure alarm, and the proportioning system) are all upstream from the flowmeters
Does a manual positive-pressure leak test check the integrity of the unidirectional valves?
No
This test does not check the integrity of the unidirectional valves
