AGM Flashcards
Check valves
Prevent backflow of gas
Gas can only flow in one direction
Found all over AGM
Pressure regulator
Drops pressure
Drops pressure from tanks (2000psi) to intermediate pressure (50psi)
2nd stage pressure regulator drops pressure from intermediate to low pressure (16psi)
High pressure system
750-22200psi
Cylinders
Cylinder pressure gauge
Cylinder pressure regulator
Hanger yoke
Yoke block with check valve
Intermediate pressure
40-50psi
Ventilator power inlet
Check valves
Pressure gauges
Flow meter valves
Oxygen pressure failure devices
Oxygen second stage regulator
Flush valve
Low pressure system
16psi
Flow meter tube
Vaporizers
Check valves
Common gas outlet
Low pressure leak test
Fail if suction bulb inflates within 10 seconds
Needs to be done everyday before 1st case
Should be repeated with vaporizers off and on
High pressure leak test
Fail if circuit does not remain pressurized at 30cm h2o
Close APL valve to pressurize circuit
Should be done between every patient and when circuit is changed
SPDD
Supply
Processing
Delivery
Disposal
Supply (SPDD)
Gases from cylinders and wall
Electricity from power cord
Processing (SPDD)
How AGM prepares gases before delivery
Delivery (SPDD)
Circuit brings gases to the patient
Disposal (SPDD)
Scavenger system removes gases from the breathing circuit
Can only remove an amount equal to FGF minus volume lost to 02 consumption
Too much removal - negative pressure in circuit
Too little removal- risk of barotrauma
APL (spontaneous breathing) and ventilator spill valve control gas going to scavenger
Parts of the scavenger
Gas collection assembly
Gas disposal tubing
Gas disposal system (gets gas from scavenger to earths atmosphere, active uses suction, passive relies on positive pressure and no suction)
Transfer tube
Interface (open vs closed)
Convenience receptacles
Found on back of AGM
Protected by circuit breakers or fuses
In theory, blowing a fuse should not affect operating of the AGM
Devices not requiring electricity
Spontaneous ventilation
Mechanical flow meters
Scavenging
Laryngoscope
IV bolus or infusion
Peripheral nerve stimulators
Five senses
Bypass vaporizers
Devices requiring electricity
Ventilators
Monitors
Lights
Digital flow meters
Bypass pumps and oxygenators
Warming blankets
Gas vapor blenders (Tec-6) or vaporizers with electronic controls (Aladin, Aisys)
Open interface
No mask on face
Open to atmosphere
Only used with active systems (suction)
Risk of healthcare team exposure
Contains reservoir
Too much suction- room air entrained
Too little suction- waste gas goes to healthcare team
No positive or negative pressure valves
No risk of barotrauma
Closed interface
Mask on face
Uses pressure valves
Doesn’t remove fresh gas from circuit
If passive- needs positive pressure relief
If active- needs both positive and negative pressure relief
Contains reservoir
5 tasks of oxygen in AGM
O2 flush valve (25-75 LPM)
O2 supply failure (less than 30 psi)
O2 pressure failure (fail safe, prevents hypoxic mixture)
Ventilator drive gas (to bellow, jet devices, auxiliary flow meter)
Flow meters (circle system-> patient)
PISS
Pin index safety system
Prevents cylinder from misconnection to AGM
Defeated if more than one washer used, or pins are removed or missing
PISS for air, O2, and Nitrous oxide
1,5
2,5
3,5
DISS
Diameter index safety system
Prevents gas hose from misconnection
Cylinder sizes
E- 2x4 (travel size, what we mostly see)
H- 4x9 (bedside when no pipeline available, in OR as N2 compressed gas)
Capacity and PSI of O2
660L, 1900-2200psi
Capacity and psi of air
600L, 1800psi
Capacity and psi for N2O
1600L, 745psi
How to determine what is left in N2O?
Weigh cylinder
Tank will read 745psi until all liquid is gone
Once liquid is gone, tank has 1/4 left
Change tank if psi drops below 745psi
Most fragile part of cylinder?
Cylinder valve
Cylinder valve parts
Body
Gas exit port
PISS
Safety relief
Conical depression for securing screw
What is the safety relief device of the cylinder valve?
Releases contents in a controlled fashion in the case of a fire (rather than exploding)
Hanger yoke
Orients cylinder
Provides gas tight seal
Ensure unidirectional flow
Contain a filter
Check babe to minimize transfilling
What is the safety release device made of?
Fusible plug made of woods metal
Frangible disc that bursts under pressure
Valve that opens under extreme pressure
Cylinder safety
No oils
Keep closed when not using
Don’t interchange regulators or gauges
Open slowly
Don’t stand up in their own
Temperature under 130 F
New washer for every tank
How is oxygen produced?
How is it delivered to hospital?
How does hospital deliver it?
Fractional distillation of liquid air
Delivered to hospital and stored as liquid at 184c
Hospital converts to gas and supplies pipeline at 50psi
Shut off valves in OR suite
To isolate leaks and interrupt supply in case of fire
Possible problems with pipeline supply
Pressure loss
Cross contamination
Cross connection
Leaks
Theft
How will you know of loss of pipeline supply?
What alarms will sound?
Indicated by pipeline pressure gauge
If pressure loss is profound, oxygen low pressure alarm sounds, and fail safe valves halt delivery of other gases
Guideline for oxygen pipeline supply failure
Trust that there is failure
Turn in back up oxygen cylinder
Call for help
Use low flow oxygen
Turn off vent and bag
Calculate time on cylinder
Do not reconnect patient until pipeline is tested
Ventilate with oxygen or room air via bag valve mask
Oxygen pressure failure device
“Failsafe”
Alarms when oxygen pressure is below 30psi (depleted tank, drop in pipeline pressure, disconnected oxygen hose)
Monitors for low oxygen pressure
Does NOT alarm for pipeline crossover and won’t detect a crack in flow meter
When this alarms, flow of N2O will stop
Hypoxia prevention safety device
Does not allow a hypoxic mixture
Flow meters are mechanically linked
Flows are pneumatically connected
Maintains O2:N2O at 1:3, or 25% oxygen minimum
When will a hypoxic mixture not be detected with hypoxia prevention safety device?
Pipeline crossover
Leaks distal to flow meter valves
Administration of 3rd gas
Defective mechanic or pneumatic components
Flow meters
Delivers gas to patient circuit
Receives low pressure
Needle valve
Thorpe tube is gas specific and tapered with largest diameter at top
Float ball - read in the middle (all other read at top)
Reynolds number
Predicts flow rate
= (density x diameter x velocity) / viscosity
<2000- laminar
2000-4000- transitional flow
>4000- turbulent
Fio2 calculation
((Air flow rate x .21) + oxygen flow rate) / total gas flow rate
Nasal canula delivered fio2
0-21%
1-24%
Then add by 4
Max at 44%
Steps in fresh gas coupling
1- convert FGF to ml/ min
2- multiple FGF by IE ratio
3- divide by breathes per minute
4- add this to tidal volume on vent to get final answer
Things that increase delivered tidal volume
Decreased RR
Increased IE ratio (from 1:2 to 1:1)
Increased fresh gas flow
Increased bellows height
Things that decrease delivered tidal volume
Increased RR
Decreased IE (from 1.2 to 1.3)
Decreased fresh gas flow
Decreased bellows height
Compliance
change in volume / change in pressure
Positive pressure in breathing circuit causes gas to expand, this won’t reach patient and must be subtracted from Vt
Variable bypass vaporizer
Does not require electricity
Agent specific
Temperature regulated
Splitting ratio
Output and flow rates accuracy
Inaccurate at low rates below 250ml/ min and will output less than dial setting
Inaccurate at extremely high flow rates and will output less than dial setting
Pumping effect
From positive pressure ventilation or use of O2 flush valve
Causes gas to re enter vaporizing chamber
Increases vaporizer output
Pumping effect is enhanced by
Low FGF
Low concentration dial setting
Low levels of liquid anesthetic in vaporizing chambers
Most common cause of vaporizer leak
Loose filler cap
Most common location of vaporizer leak
Internal leak in vaporizer
When is a vaporizer leak detected?
Only when turned on
What to do when vaporizer is tipped
Disconnect patient ? Possible overdose
Drain vaporizer
Turn dial to highest setting and run it with high FGF for 30 minutes
Tec 6 Desflurane vaporizer
Electricity required
Heats to 39c
Pressurizes to 2 ATM
Does not compensate for pressure changes- higher altitude requires higher dial setting, lower altitude requires lower dial setting
First device to detect oxygen pipeline crossover?
Oxygen analyzer
Are the oxygen pressure device and hypoxia prevention safety device designed to detect oxygen pipeline crossover?
No
What is the last line of defense for hypoxic mixtures?
Oxygen analyzers
2 types of oxygen analyzers
Galvanic fuel cell - needs daily calibrations
Pragmatic device - self calibrating and faster response
What does the oxygen analyzer do?
Monitors oxygen concentration
Oxygen flush valve
25-75LPM 50psi
Can cause barotrauma
Excessive use can lead to patient awareness
Ventilator spill valve
When open- during exhalation, excess gas goes to scavenger
When closed- Ensures Vt goes to patient and not scavenger
Intrinsic PEEP
Pneumatic ventilators only
Prevents build up of volume and pressure in breathing circuit
HME advantages
Filters large particles
Filters bacteria and viral
Retains heat and moisture from breathing circuit
Inexpensive
No water or electricity required
No risk of hyperthermia, overhydration, burns, electrical shock
Disadvantages of HME
Not as effective as water based electrical devices
Increase dead space
Obstruction can occur
If increased airway resistance is noted, pressures should be measured with and without HME to assess for mechanical deficits
Pneumatic bellow ventilator
Classified based on movement of bellow
Double circuit
Force of compressed gas (air or O2) as driving mechanism
Leaks in bellows may dilute gas with driving gas and cause hypoxia (if bellows are driven on air), increased fio2 (if bellows are driven on O2), or awareness (loss of agent)
Ascending bellows
Standing
Ascend during expiration
Safer
Will not fill if a total disconnection occurs
Descending bellows
Hanging
Descend on expiration
Will continue motion if disconnection occurs
Must have co2 / apnea alarm
Modern Piston ventilator
Uses an electric motor to compress the position to generate positive pressure
Doesn’t use oxygen to run the ventilator
Doesn’t deplete o2 tank in pipeline failure situation
2 pressure relief valves - positive (opens when pressure is too high) and negative (entrains air when too much negative pressure occurs)
Decouples FGF for consistent Vts
Volume controlled
Delivers preset Vt over predetmines time
Pressure depends on compliance
Inspiration flow is constant during inspiration
Resistance increases PIP
Pressure controlled
Set pressure for every breath
Vt and flow vary based on lung compliance
Resistance decreases Vt
Inspiratory flow is decelerating; starts high to achieve pressure then slows to maintain pressure
What decreases Vt in PCV
Pneumoperitoneum
Trendelenburg
Brochospasms
Kinked ETT
What increases Vt in PCV?
Release of pneumoperitoneum
Going from trendelenburg to supine
Bronchodilator
Removing secretions
When is PCV better than VCV?
Low compliance- obesity, pregnancy, ARDS, laparoscopy
High PIP would be dangerous- LMA, neonate, emphysema
Need to compensate for a leak- LMA, children with an ETT
Breathe types
Controlled- machine triggered and machine cycled
Assisted- patient triggered but machine cycled
Spontaneous- patient triggered and cycled
Controlled mandatory ventilation (CMV)
Machine initiates breathe and gives preset Vt and RR
Asynchrony can occur
Best for apneic patients
Assist control
Machine initiates breathe and gives preset Vt and RR
Spontaneous breathe receives full Vt
Can lead to hyperventilation
SIMV
Machine initiates breathes at preset Vt and RR
Patient can breathe between machine breathes
Better synchrony
Spontaneous breathes can be augmented with pressure support
Great for weaning and LMAs
Guarantees minute ventilation
PCV- VG
Pressure control mode
Only uses pressure needed to achieve goal Vt
Great for cases with compliance changes like laparoscopic procedures
PSV
Augments spontaneous breathes with set amount pressure support
Only supports inspiration
No machine initiated breathes
Great for weaning and LMAs
PSV-Pro
Spontaneous breathing patient will get PSV
Apneic patient will get PCV
Once patient starts breathing, will resume PSV
Great for weaning and LMAs
CPAP benefits
Augments spontaneous breathing
Reduces airway collapse on expiration
Bipap benefits
COPD patients
Airway pressure release ventilation
Spontaneous ventilation only
Like bipap but high level of CPAP through most of respiratory cycle
Good for ARDS
Inverse ratio ventilation
Respiratory cycle is divided into inhalation and exhalation (IE determines time in each)
Exhalation is typically longer
IRV gives more time to inspiration
Pt must be paralyzed
Used in ARDS with small FRC
High frequency ventilation
Vt below dead space is delivered at high RR
Gas transport occurs via molecular diffusion, coaxial flow, and high velocity flow
Types- jet, oscillation, percussive
CO2 absorber
Removes exhaled CO2
Base neutralizes an acid
Needed for closed and semi closed circuits
Mesh size
Must balance surface area and airflow resistance
Best balance with 4-8 mesh granules
Each granule 1/4 to 1/8 inch and pass thru mesh screen with 4-8 holes per square inch
Exhaustion
No longer able to neutralize CO2
Must change double canister at same time
Increasing MV will not decrease ETCO2
CO2 Desiccation
Absorbent is too dry
Don’t add water - fire risk
Soda lime
When exhausted and PH below 10.3- REPLACE
Best indicator for changing- inspired CO2
Does not regenerate even when colors go back to normal color
Produces CO- mostly with Sevo, then iso, des
How to minimize Compound A
Low FGF
Turn off between cases
Change all absorbent at once
Change canister when it’s purple
Change canister if unsure
Calcium hydroxide Lime
Uses calcium hydroxide instead of a strong base
Also contains calcium chloride which keeps it moist
Benefits over soda Lime- no CO, no compound A, lower fire risk
Drawback- needs more frequent changes, costs more
Most common cause of low pressure in breathing circuit
1- Circuit disconnect (most common Y piece)
2- CO2 absorber (poor seal, defective canister)
What to do if circuit won’t hold pressure
Ambu bag
TIVA
Monitors for circuit disconnect
Pressure
Volume
ETCO2
Vigilance
What to do when sustained high pressure curcuit
Bag mode
Manually ventilate patient
Treat causes
If pressure is sustained- scavenger obstructed, scanner relief valves failed, disconnect scavenging system if possible, ambu
If pressure is relived- ventilator relief valve is malfunctioning - DO NOT USE!
OSHA recommendations
Halogenated- <2ppm
N2O- <25ppm
Both combined- <0.5 ppm and 25ppm
Determinants to excess of waste gas
OR ventilation and air turnover
Functional status of anesthesia equipment
Mask fit
Gas on only after mask fit
Turn of gas before suctioning patient
Cuff ETT
Evacuate gasses to scavenger at end of case
Monitor AGM for leaks
TIVA
Avoid N2O
Use low FGF
Do not spill agents
APL
Controls gas going to scavenger system in spontaneously breathing patients
Ventilator spill valve
Controls gas going to scavenger in mechanically ventilated patients
Valves of the anesthesia machine
Free floating valve
Ball and spring valve
Diaphragm valve
Free floating valve
Only valve that floats in the middle
Moves in the direction of push of gas flow
Prevents gas from leaking
Found in DISS and dual hanger yoke system
Ball and spring valve
O2 flush
40-50psi
Anesthesists panic button
Diaphragm valve
First stage regulator (high to intermediate)
Second stage regulator (intermediate to low)
