Anesthetic Machine Equipment Flashcards
Considerations
- anesthetic concentration control
- build up of carbon dioxide
- consumption of oxygen
- atmospheric pollution
- patient size
- airway control
Liquid anesthetic dissolves ______
Organic compounds
- skin cells/mucosa/eyes
- wear protective equipment when refilling vaporizer
Is the oxygen source part of the anesthetic machine?
No
Anesthetic machine components
- gas source
- regulator
- flowmeter
- vaporizer
- O2 flush and bypass valves
- common gas inlet
- CO2 absorbent canister
- patient breathing circuit
- adjustable pressure limiting valve
- rebreathing bag
- waste gas scavenger
Regulator
Decreases high pressure to intermediate pressure
Flowmeter
Allows you to adjust liters/minute of 100% O2 patient is receiving
Vaporizer
Contains liquid anesthetic
O2 flush
Oxygen from cylinder will bypass flow meter and vaporizer and go directly into the patient’s lungs (dangerous)
- used to remove excess anesthetic after patient is disconnected
Common gas inlet/outlet
Where fresh gas (O2 + vapor anesthetic) comes out into the anesthetic circuit
CO2 absorbent
Clear/look for color change in beads
Patient breathing circuit
Part that is attached to patient ET
APL/Pop-off valve
Allows extra pressure from circuit to be relieved
- when closed all the way, there is no where for air to go (air enters rebreathing bag from patient)
- when open it allows air to escape, preventing trauma to lungs
Rebreathing bag
Attached to anesthetic circuit
Waste gas scavenger
Attached to wall or activated charcoal
High pressure area
Up to 2200 psi = 150 atmospheres
- includes tanks, yokes, and hangers (regulator inlets)
Intermediate pressure area
35-50 psi = 2.3-3.4 atmospheres
- includes central pipeline hoses and regulator outlets to flowmeters and flush valve
Low pressure area
14.7 psi = 1 atmosphere = 760 mmHg
Medical gases
- primary: banks of G or H cylinders, or bulk liquid tank
- secondary: small compressed gas cylinders attached to the hanger yoke
Carrier gases
- oxygen
- nitrous oxide
- supplied in cylinders as a gas (O2) or liquid (NO) under pressure
Cylinder ID - color
- oxygen: green (US) or white (EU, AU)
- NO: blue
Cylinders are ______, but not ______
Flammable; explosive
Gas supply safety
Noninterchangeable, gas-specific connections help prevent mixups
Gas cylinder handling
- properly secured at all times (inclu. transport)
- stored in cool, dry, clean, well-ventilated rooms constructed of fire-resistant materials
- crack valve briefly before mounting on yoke to clear debris
Do NOT use ____ on cylinder valves
Oil!
Calculating volumes
- H tanks = 6900 L at 2200 psi
- E tanks = 660 L at 2200 psi
How many liters in an E tank reading 750 psi?
660 L at 2200 psi
____ at 250 psi
- 75 L at 2 L/minute
- 37 minutes left
Pressure regulator
Aka: pressure reducing valve
- reduce high cylinder supply pressure (up to 2200 psi) to a constant lower working pressure (35-50 psi)
- constant flow rate of gas to the flowmeter (down stream)
Flow meters
Thorpe tubes (15 psi)
- change in annular opening size results in changes in L/min
- Bobbins/indicators
Flowmeter function
- precisely measure gas flow
- tapered glass tubes with floats
- gas-specific –> parts can not be interchanged
- oxygen flowmeter always closest to patient
Oxygen flush valve
Bypasses vaporizer
- delivers large volumes of oxygen to breathing circuit
- is under higher pressure (caution!!)
Vaporizer function
Provide a means for anesthetic vapor to be combined with the carrier gas in a controlled manner
Vaporizers
Most inhalant anesthetics have saturated vapor pressures far exceeding the amount required for clinical anesthesia
- for iso, saturated vapor pressure would be 240/760, or 31.6% –> 1 MAC equals 1.4%
- change liquid anesthetic into saturated vapor
- add specific amounts of anesthetic vapor to other gases being supplied to patient
Vaporizer physics
Heat is required to vaporize liquids –> latent heat of vaporization!
- vapor pressure of a liquid varies with temperature
- over time, temp and anesthetic vapor pressure will decrease
- heat can be added by using substances with high specific heat and thermal conductivity
Vapor classification
Output regulation!
- calibrated, temp, flow and backpressure compensated, variable-bypass type
–> cyprane tec series, ohio calibrated, drager vapor series, abingdon, bickford
Non-calibrated, non-compensated type (simple agent nonspecific)
- stephens, ohio #8
Precision vs non-precision
- precision: deliver same amount of vapor anesthetic throughout
- non-precision: you do not know how much is getting into the lungs, changes with room temp
Precision vaporizer
Known concentration
- temperature compensated (manual or automatic)
- flow compensated (manual or automatic)
- high resistance
- agent specific
Non-precision
- no temperature or flow compensation
- not agent specific
- precise concentration not known
Precision (calibrated) vaporizer resistance
Constant output over time for a wide range of flows and environmental temperatures
- high resistance to flow
Simple (noncalibrated) vaporizer resistance
Output varies with changes in temperature and flow through the vaporizer
- low resistance to flow
Vaporizer location
Depends on resistance characteristics of vaporizer
- calibrated vaporizers (high resistance): vaporizer placed out of circuit
- noncalibrated vaporizer (low resistance): vaporizer in circuit
Vaporizer troubles
- filling errors: drain vaporizer, high O2 flow until dry
- tipping beyond 45 degrees can allow liquid to enter gas lines: high O2 flow at low dial settings for 20 min
- concurrent use of 2 vaporizers: excessively deep anesthesia
- vaporizer connected backwards: excessively deep anestheia, liquid into lungs
Circle breathing systems
2 one way valves to prevent rebreathing
- adult
- pediatric
- large animal
Non-rebreathing systems
CO2 pushed out of system with oxygen flow without rebreathing
- needs a higher flow, O2 needs to be 150-300 kilos/min
- mapleson F
- jackson rees w/ modified Arye’s T
Mapleson D requires a ______
Bain block
Bain circuit
Recommended for patient’s that weigh less than 5 kilos
- could be used in larger patients but you would waste oxygen and anesthetic due to high flow rate
Bain circuit limitations
Limited by the size of an animal that can be connected to it and the cost of gas/inhalant
- applies to any non-rebreathing system
Reservoir/rebreathing bag
- part of the circle
- supplies peak inspiratory demands
- can ventilate with it
- monitor ventilation rate
- connection is where a mechanical ventilator is attached
One way valves
On inspiratory and expiratory limbs
- plastic disk needs to be present in order to be a one way valve
One way valves are ______ in circle system, _____ in nonrebreathing system
Present; absent
CO2 absorbent canisters
- react with CO2 to remove it from the air
- are not present in nonrebreathing systems
- soda lime is the absorbent
- usually lasts 6 hours
Soda lime/barium lime
Exothermic reaction: heat not present when the soda lime is exhausted
- granules contain indicators (dyes) which change color as the soda lime becomes exhausted (white to purple)
- change in feel: exhausted granules are harder
Overflow or pop-off valve
Escape route for excess gas and pressure
- gases enter into scavenging system
- valve is closed during mechanical ventilation
Scavenging of waste gases
- active evacuation
- passive evacuation
- absorption canister
Scavenging systems
- active = negative draw
- piped to atm via connector in wall
- interface: closed or open
Circle system - advantages
- less environmental pollution
- heat/humidity conservation
- slower changes in anesthetic plane
- less gas consumption
Circle system - disadvantages
- many components
- high resistance due to the presence of the uni-directional valves and soda lime canister
Universal F circuit
Coaxial circuit
- rebreathing system
Wash-in of anesthetic gases
Change in gas concentration within enclosed spaces involves:
- wash-in of new gas
- time constant required for that change to occur
Time constant
Rate of change of gas concentration within a breathing circuit can be predicted from the time constant
- time constant = circuit volume/gas inflow rate
- one time constant = 63% desired conc.
- 3 time constants required to make a 95% change in concentration
- 4 time constants = 98%
Increasing the flow rate _____ the time constant
Decreases
Checkout recommendations
- evaluate high, intermediate, and low pressure areas of the anesthesia machine
- check breathing circuit for leaks
- occlude patient connection, close APL valve
- inflate circuit with O2 to 30-40 mmHg
- observe for leaks
- open APL valve and note that scavenger is not obstructed
