2 - Anesthesia Machine Flashcards
Most important item in the preuse checklist
Functioning self-inflating resuscitation bag (SIRB) and full auxiliary tank of oxygen
What is the “vulnerable” area of the workstation?
Why?
Low pressure circuit (LPC)
Most subject to breakage and leaks, and also downstream from most detectors
What is the only sensor monitoring LPC integrity in an ongoing fashion?
Oxygen Analyzer
Which test checks the integrity of the anesthesia machine from the flow control valves to the common gas outlet?
LPC leak test
Why are flowmeter leaks a significant hazard?
They are downstream from any safety sensor except the oxygen analyzer
What is the calculation for pressure?
P = Force/Area
What is PSI?
Pounds per square inch
What is a boiling point?
The point at which liquid becomes gas
What four actions should you immediately take if pipeline pressure is lost or crossover is suspected?
- Turn on the backup oxygen cylinder
- Disconnect completely the wall/pipeline supply
- Turn off the ventilator and use the circle system
- Convert to total IV anesthesia
Leaks in the LPC can lead to:
delivery of hypoxic injury
awareness during anesthesia
Which gas requires specialized vaporizers?
Why?
Desflurane
Has a low boiling point and high vapor pressure
The APL valve prevents what kind of injury?
barotrauma
The LPC leak test checks the integrity of the machine from _____ to _____
flow control valves
common gas outlet
What is present at the pipeline inlet?
filter
check valve
pressure gauge
What does a check valve prevent?
Leakage when the supply is disconnected
What is a common factor related to patient injury during cross-connection?
Failure to use an oxygen analyzer
What would you see in the event of a crossover?
declining inspired O2 concentration
When should cylinders be open?
Only when they are checked or when pipeline supply is unavailable
What system uses PISS?
DISS?
Cylinder
Pipeline
PISS for O2?
N2O?
Air?
2-5
3-5
1-5
Psi in an O2 tank?
Nitrous?
Air?
1900
745
1900
Capacity of an O2 tank?
Nitrous?
Air?
660
1590
625
What is the most fragile part of the cylinder?
Cylinder valve
Why is transfilling a potential fire hazard?
filling a cylinder produces heat! Gas laws!
The cylinder pressure gauge is what kind of gauge?
Bourdon
Cylinder pressure is ______ than pipeline pressure
slightly lower (45 vs 50)
If a cylinder is open and the gas pipeline shuts off, will you get an alarm?
Not until the cylinder is empty
Using the ventilator, how long will a full tank of O2 usually last?
1 hour
When does the low oxygen supply failure alarm go off?
At the end of the emergency supply, instead of its beginning
Why is hospital compressed air drier than atmospheric air?
Dehumidified to prevent damage to equipment
New anesthesia machines are equipped with at least ______ backup power
30 min
Which items do not rely on electrical supply?
spontaneous/assisted ventilation
manual blood pressure cuff
mechanical flowmeters
variable bypass vaporizers
What is fail safe valve?
Held open by O2 flow
Closes when O2 flow stops
prevents flow of hypoxic mixture to patient
Not present on O2 or air
What are the five tasks of oxygen?
- proceeds to fresh gas flowmeter
- Powers the oxygen flush
- Activates fail safe mechanisms
- Activates oxygen low pressure alarms
- Compresses the bellows of mech vent
All gases except oxygen have ______ pathway.
One: to patient via flowmeter
Which valve controls gas flow through the flowmeter?
Needle valve
What are the components of a flowmeter?
knob
needle valve
valve stops
flowtube
indicator float
Why is the flowtube referred to as a variable orifice flowmeter?
the annular opening around the float is larger at higher flows
Never adjust a flowmeter without _________
looking at it
Failure to turn the flowmeters off at the end of the case can result in damage to what?
CO2 absorber
Generates CO in canisters
can cause canister fires
When should the auxiliary oxygen source not be used?
During pipeline failure/crossover
Common gas outlet flowmeters
Shows pipeline flow as a backup on machines with electric flow displays
How much gas is a flush valve required to provide?
35-75 L/min
When should you NEVER active O2 flush?
During the inspiratory phase
How can you inflate the bellows without flushing?
Increase fresh air flow to 8-10 L/min
Compare old and new low pressure alarms?
Old ones sounded like a whistle
New ones are electronic
In proportioning systems, the ration of nitrous to oxygen is never greater than _______
3:1
What are four situations where the hypoxic guard system allows hypoxic mixing?
- Wrong gas in pipeline/tank
- Defective pneumatics/mechanics
- Leaks downstream of flow control valves
- Inert gas administration (i.e. helium)
What is the only system that ensure oxygen is present in the breathing circuit?
Inspired oxygen analysis
Monitoring inspired oxygen is required in what circumstances?
Every general anesthetic
When should the oxygen monitor be checked?
Before every case, even if general anesthesia is not anticipated
What are the two types of inspired oxygen sensors?
Paramagnetic and galvanic
What is a vapor?
Liquid at room tempreature and 1 atm
Measured flow (vernitrol) vaporizers require manual ___________
temperature compensation
What’s the difference between variable bypass and Tec 6 inejctor vaporizers?
Air flow: in variable bypass flow passes over liquid agent, in Tec 6 fresh gas never comes into contact with the liquid agent
Tec 6 is heated
In VB % is acheived by modulating flow
in Tec 6 % is acheived by modulating heat
How is an operator prevented from giving more than one vaporized gas at a time?
Interlock system
What is optimal wash-in?
Using high fresh gas flow (nonrebreathing @ 5-8L/min) during induction, and using low fresh gas flow during maintenance
The degree of rebreathing is increased as ________ is decreased
fresh gas flow
The higher the fresh gas flow, the more quickly the composition of gas in the breathing circuit will resemble __________
the dialed in concentrations at the common gas outlet
Rebreathing of exhaled nitrogen _______ induction.
Slows
What effect does dead space have on degree of CO2 rebreathing?
Increased dead space = increased rebreathing
Which has more dead space: a facemask or an ETT?
A facemask
Where does dead space end on a breathing circuit?
The y piece
Why is emergence not the same thing as passively waking up?
Decreased concentrations of inhaled gases cause wash out while ventilation is continued
Circle system at high fresh gas flow (greater than minute ventilation) is considered open or closed?
semi-open
No rebreathing
Circle system at low fresh gas flow (less than mV) is open or closed?
Semi closed
Partial rebreathing
Circle system at extremely low fresh gas flow with APL valve closed is open or closed?
Closed
Complete rebreathing
What are common features of nonrebreathing systems?
Lack unidirectional valves
lack soda lime carb dioxide scrubbers
fresh gas flow determines the amount of rebreathing
Resistance and work of breathing are low
Circle system allows rebreathing of ________ but not ________
All other gases
CO2
What are the two common reasons for increased inspired CO2 in a circle system?
exhausted CO2 scrubber
faulty unidirectional valve
If more than 1-3 mmHg of inspired CO2 is present in a circle system, what should you do?
What if that doesn’t work?
Increase the fresh gas flow to 5-8 L/min
This converts the system into a semi-open system, which minimizes rebreathing
If it works, the problem is the scrubber. If it doesn’t the problem is a valve.
How do you check unidirectional valves before use?
Spare breathing bag on the y piece, observe the valves lifting and falling. Test with both ventilator and circle.
What happens when sevoflurane encounters soda lime?
Produces Compound A which is lethal in rats and can cause renal damage
You should not use sevo with gas flows less than _______ and more than ______ hours
1-2 L/min
2 MAC hours
Degradation of Desflurane in soda lime produces what?
carbon monoxide
Do CO2 scrubbers significantly increase circuit resistance
No. Creates less resistance than the ETT.
What are early clinical signs of CO2 scrubber exhaustion?
Increased EtCO2 and inspired CO2
Respiratory acidosis
hyperventilation
SNS activation
Bleeding at surgical site
+ color change
What are late signs of carbon dioxide scrubber exhaustion?
Increased (then decreased) HR and BP
Dysrhythmia
A higher fresh gas flow will ____ the lifetime of a scrubber
increase
What is the current recommendation for Vt?
RR?
I:E?
5-7ml/kg IBW
6-12
1:2
How should you adjust the ventilator if end-expiratory flow is incomplete before the next waveform begins?
Decrease RR
Prolong the I:E
Which patients may benefit from PCV?
those for whom high inspiratory pressure is dangerous:
Neonates
laryngeal mask airways
emphysema
What should you think first when there is a change in the patient’s condition is noticed?
Think back to the last alteration made to the equipment, or last drug given, and determine if that could be responsible
What is the threshold for smelling anesthetic gases?
5-300 ppm
ALWAYS ABNORMAL
What is fresh gas decoupling (FGD)?
Circle breathing system where fresh gas is piped into the resevoir bag during the inspiratory phase. When the expiratory phase begins, the gas in the resevoir bag flows into the bellows and is given with the next breath, and so the Vt includes the amount of fresh gas.
What is the greatest disadvantage of FGD?
increased possibility of air entrainment that dilutes the fresh gas and could go undetected.
Also, can’t be any problems with the resevoir bag
Which machine uses FGD?
Drager
Which machine dispenses with the need for a bellows or piston for PPV?
How?
The Maquet FLOW-i
Uses a volume deflector
Why is the volume reflector more economical than a bellows or piston?
fresh gas flows into the reflector only during the inspiratory phase rather than continuously throughout the respiratory cycle
