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What agency sets the standard for the anesthesia workstation in the United States?
- American Society for Testing & Materials
What is the current anesthesia gas machine standard?
Can older anesthesia machines be updated to meet new standards?
What are the 13 required components of anesthesia machines?
- 1) 30 minute battery backup
- 2) alarms: high, medium, and low priority
- 3) Monitors
- 4) Hypoxic guard system
- 5) Gas monitoring
- 6) Pulse oximetry, EKG, and BP monitoring
- 7) Breathing circuit pressure limited to 125cmH2O (12.5kPa)
- 8) Detachable resistant or non-detachable electric supply cord
- 9) At least 1 backup oxygen cylinder
- 10) Flowmeters
- 11) Auxillary oxygen flowmeter recommended
- 12) Oxygen flush capable of 35-75lpm that bypasses vaporizers
- 13) Vaporizer features
What does the 30 minute battery backup depend on?
Rate of power consumption; it assumes you're hand ventilating
What is a specific requirement regarding high priority alarms?
Cannot be silenced >120 seconds
What is required of alarms?
Must be automatically enabled and functioning prior to use by turning the machine on or by following the pre-use checklist
What 3 alarms are required?
- 1) breathing circuit pressure
- 2) oxygen concentration
- 3) exhaled volume and/or ETCO2
What are triggers for high priority alarms?
- 1) user adjustable limits are exceeded (high peak airway pressure)
- 2) continuing high airway pressure (APL valve closed)
- 3) Negative pressure (attempted inhalation against obstruction)
What may disconnect alarms be based on?
- 1) low pressure
- 2) exhaled volume
- 3) CO2
What 3 monitors are required?
- 1) exhaled volume
- 2) inspired oxygen with high priority alarm within 30 seconds if oxygen < 18% (or user set limit)
- 3) oxygen supply failure alarm
What does the hypoxic guard system protect against?
<21% oxygen mixture when nitrous oxide is in use
What is required of the backup oxygen cylinder?
- 1) a PISS hanger yoke
- 2) clamping device that resists leaks
- 3) a filter
- 4) check valve to prevent trans filling tank-to-tank
- 5) cylinder pressure gauge
- 6) cylinder pressure regulator
- 7) the machine must use pipeline gas as long as pipeline pressure >50psi (345kPa)
What is required of flowmeters?
- 1) single control for each gas
- 2) each flow control is next to flow indicator
- 3) uniquely shaped oxygen flow control knob
- 4) valve stops to prevent excessive rotation and flowmeter damage
- 5) oxygen flow indicator is to the right side of the flowmeter bank
- 6) oxygen enters the common gas manifold downstream of other gases
What are features required of vaporizers?
- 1) concentration-calibrated
- 2) interlock system
- 3) liquid level indicator to prevent overfilling
- 4) "should" used keyed-filler devices
- 5) no discharge of liquid anesthetic occurs from vaporizer even at maximum fresh gas flow
What does the master switch control?
Electrical and pneumatic system
What does the mains power switch control?
AC power into the machine
If the master switch is on but AC inlet is off, can the machine be on?
Yes but it is on battery power and the electrical outlets are off.
What do you do in the event of a power failure?
- 4 Cs
- Check power cord
- Check outlet
- Conserve power
Why should the anesthesia machine be plugged in when not in use?
To charge the battery
What are electrical outlets on the back of the machine designed for?
- Do not use for any device that produces heat: bair hugger, fluid warmer, bovie
- Not powered if machine is unplugged or mains power switch is off
What do you do if the circuit breaker trips on the electrical outlet on back of machine?
Reduce load, reset breaker
What 3 sub-systems compose the pneumatic system?
High, intermediate, and low pressure
What are the components of the high-pressure system?
- 1) gases from cylinder at variable pressure from hanger yoke
- 2) PISS, nipple, and O-ring
- 3) debris filter
- 4) check valve
- 5) cylinder pressure gauge
- 6) primary pressure regulator
What is the pressure change on the primary pressure regulator?
Tank pressure (800-2200psi down to 50psi for Oxygen; 745 to 50psi for nitrous)
What is the purpose of cylinders on the back of the anesthesia machine?
Backup only, not a primary source of gas
What type of lubricant should be avoided on the hanger yoke/o-ring?
Petroleum based products - may cause adiabatic explosion if there is a rapid increase in heat when tank turned on quickly in the presence of a petroleum fuel
What component of the high-pressure system prevents the need for continuous readjustment of flows as the tank empties?
Primary pressure regulator
What is the use of a yoke plug?
- Placed in hanger yoke when cylinder is empty and another is not available
- Backup to prevent gas escape in the event of check valve failure
What are the components of the intermediate pressure system?
- 1) gases from either pipeline connection (50-55psi) or pressure regulated gases from the high pressure system (45-50psi)
- 2) check valve to prevent backflow into pipeline
- 3) filter
- 4) gauges for pipeline pressure
- 5) pressure relief valve to avoid over-pressurization
- 6) flush valve
- 7) master switch - pneumatic component
- 8) oxygen failure safety device
- 9) secondary pressure regulator
- 10) flow control valves
What is the final component of the intermediate-pressure system?
What safety system is used at the pipeline connections to the anesthesia machine?
What is the route of flow for the O2 flush valve?
Directly from the first-stage pressure regulator to the common gas outlet at 35-75lpm @ 45-55psi
What does the master switch do in the pneumatic system when turned off?
Vents all pressure in the intermediate system and beyond to zero
What is the function of oxygen pressure failure devices?
Prevent delivery of gas mixture that does not contain oxygen
What is another name for the oxygen failure safety device?
What does the oxygen failure safety device do?
- Either shuts off or proportionally decreases and eventually shuts off non-oxygen gas flow
- Prevent nitrous only gas flow in the event of loss of oxygen pressure
What does the oxygen supply failure alarm do?
- Sounds in less than 5 seconds when oxygen pressure less than 30psi
- Prevents inhalation of gas containing <21%
What is a major limitation of the oxygen failure safety device and oxygen supply failure alarm?
- They do not detect the composition of the gas, only the pressure
- Do not prevent gas other than oxygen from being supplied through oxygen line
- Depend on pressure, not gas composition
What is the function of the gas selector switch?
- Prevents using a combination of air and nitrous
- Must use oxygen and air or oxygen and nitrous
What pressures does the second-stage regulator reduce oxygen and nitrous to?
- Oxygen 14 psi
- Nitrous 26 psi
Why is a second-stage pressure regulator used?
- Create fail safe with pressure difference to prevent running nitrous without oxygen
- Helps reduce pressure fluctuations at flowmeters thereby reducing flow fluctuations
Why is the oxygen control knob fluted?
So you can find it in the dark
What is required of electronic flowmeters?
Mechanical backup in the event of power failure
What are the components of the low pressure system?
- 1) flowmeters
- 2) vaporizers
- 3) auxillary or courtesy oxygen flowmeter (side-port)
- 4) common gas outlet
- 5) unidirectional valves
- 6) patient
What is the pressure of the low-pressure system?
Slightly above atmospheric pressure
What do pressure fluctuations depend upon in the low-pressure system?
- 1) total flow
- 2) back-pressure devices
- 3) back-pressure from breathing system
What is the function of unidirectional valves in the low-pressure system?
Prevent pt from breathing into the machine
What temperature and pressure are flowmeters calibrated at?
What will be the result of a large decrease in atmospheric pressure on flowmeter settings?
Will have greater than dialed flow due to reduced atmospheric resistance
What 3 things does flow rate depend on in flowmeters?
- 1) pressure drop across constriction
- 2) size of annular opening
- 3) physical properties of the gas
Where is flow most accurate in flowmeter?
Fine and coarse flowmeters are in series or parallel?
Why is oxygen on the far right of the flowmeter bank?
Safer in the event of bank or flowmeter failure to prevent hypoxic gas delivery
Are flowmeters universal?
No they're specific to each gas
What is the function of hypoxia prevention safety device?
- Older machines would have oxygen flow of 50-250ml/min when flowmeter in full off position with pneumatic system on
- Reduces nitrous flow to maintain oxygen >25%
- Aka proportioning system
What is the Ohmeda link 25 system?
Mechanical proportioning system to prevent <25% oxygen delivery with nitrous
Where are unidirectional check valves located in the low-pressure system?
- Between vaporizers and common gas outlet
- Prevent pt from exhaling into the flowmeters/vaporizers
When is APL valve used?
During spontaneous or manual ventilation
What does the APL valve do?
- Limits the amount of pressure buildup possible during manual ventilation
- Should be kept open unless giving positive pressure ventilation
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