Anesthesia Machine Flashcards
What would result from delivering atmospheric air for anesthesia?
Hypoxia- due to hypoventilation and V/Q mismatch caused by anesthetics
Minimum O2 requirement for anesthesia
30-35% O2
Atmospheric is 21%
Metabolic O2 requirement
5-10mL/kg/min
Represents the minimum O2 flow required
Gasses
O2
Nitrous oxide
Medical air
Two types of O2 cylinders
E- usually in singles, attached to machine via a yoke
H- stored in banks, central O2 supply
Green Cylinders
Oxygen
Blue Cylinders
Nitrous oxide
Yellow Cylinders
Medical Air
Why are cylinders stored on their sides?
To prevent explosion and avoid spontaneous combustion
Cylinder pressure units
psi
Breathing system pressure units
cmH2O
High Pressure systems
100-2200+psi
Gas cylinders, yokes, pressure gauges, regulators
Intermediate pressure systems
50psi
Central O2 supply, post-regulatory, flush valve, input to flowmeter, driving gas for ventilator
Low pressure systems
pressure in patients lungs
E-cylinder capacity
660L (need to memorize)
H-cylinder capacity
6600L
Internal cylinder pressure
2200psi
How do you figure out volume left in tank?
Boyle’s law
P1V1=P2V2
How do you figure out time left on remaining volume?
Minutes = Volume/(flow liters/min)
Can you calculate remaining volume on N2O tanks?
NO- exists as both a liquid and a gas in the tanks and the pressure will only read the gas portion
Components to the safety systems
- Colour coding
- Labeling
- Diameter index safety system
- Pin index system
- Quick connectors
Diameter index safety system
Non-interchangeable gas-specific threaded connection system
Universal between equipment cylinder manufacturers
Pin index safety system
Gas-specific pin patters that only allow connections between appropriate cylinder yokes and E-tanks
Commonly found on yokes and some cylinder-specific regulators/flowmeters
Quick connectors
Manufacturer-specific
Facilitate rapid connecting/disconnecting of gas hoses
Regulator
Aka pressure reducing valve
Decreases tank pressure to approximately 50psi and supplies to the flowmeter
Prevents pressure fluctuations as tank empties
Flowmeter
Controls rate of gas flow through the vaporizer (L/min)
Calibrated for 760mmHg and 20C
Flowmeter pressure reduction
50psi to 15psi
Where do you read the flowmeter?
Middle of ball or top of bobbin depending on type
Where should the O2 flowmeter be positioned if there are multiple gas flowmeters? Why?
Far right, to avoid hypoxic mixtures.
Quick flush
Delivers intermediate pressure O2 bypassing the vaporizer
Flowrate of the quick flush
35-75L/min
Use for the quick flush
Quickly decrease gas percentage in circuit
Emergency or recovery
Should the patient be hooked up to the circuit when using the quick flush?
NO- results in dangerous pressure in the breathing circuit which could result in pneumothorax
Anesthetic vaporizers
Change liquid anesthetic into vapor
Deliver selected % of vapor to the fresh gas outlet
Vapor
Gaseous state of a substance that is liquid at ambient temp and pressure
Eg- halo, iso, sevo, desflurane
Gas
Exists in gaseous state at ambient T/P
Eg. N20, Xenon
Vapor pressure
Pressure exerted by vapor molecules when liquid and vapor phases are in equilibrium
Directly related to temperature
Inversely related to boiling point
Saturated vapor pressure
Maximum administration percentage of vapor
Vaporizers reduce this to clinically useful percentages
Modern vaporizer characteristics
- Agent specific
- Concentration calibrated
- Variable bypass
- Flow over
- Out of circuit
- High resistance
- Compensated for temperature, flow, and back-pressure
Variable bypass system
Delivers a specific concentration by flowing fresh gas over a reservoir of liquid anesthetic and mixing it from carrier gas
VOC- precision vaporizer
Out of circuit vaporizer which delivers a known percentage of anesthetic
VIC- non-precision vaporizer
OLD model
Glass jar containing wicking material saturated with anesthetic
Did not deliver a precise percentage of anesthetic
Modern vaporizer compensations
Temp: Between 15-35C
Achieved using efficient heat conducting materials
Flow rate- 0.5-10 L/min
Back pressure- associated with positive pressure ventilation and flush valve
Desflurane vaporizer
Boiling point close to room temp
Electronically heated
Commonly used in Human, not in vet
Agent-specific key filler port
Prevents filling of vaporizers with improper anesthetics
Do modern vaporizers require external power?
No- except desflurane
Vaporizer transportation/orientation
Cannot be tipped, must be emptied prior to transport
If tipped run 1L/min O2 with vaporizer off to clear lines
What do you do if vaporizers are filled with the wrong anesthetic?
Drain and run 1L/min O2 until dry
Common gas outlet
Where gas exits the vaporizer, connected by a hose to the fresh gas inlet
Universal for rebreathing and non-rebreating units
