Anesthesia Machine Flashcards
What is Wood’s metal?
Fusible plus that melts at elevated temperatures.
- Bismuth, Lead, Tin, and Cadmium (BLT with Cheese)
- uses on gas cylinders
When does the oxygen pressure failure device activate?
- If the oxygen tank is exhausted.
- If oxygen pressure is the supply line is less than 20 psi
- monitors oxygen pressure, not concentration
- its also reduces/stops the flow of nitrous oxide when pressure in oxygen pipeline falls below 20 psi.
What is the hypoxia prevention safety device?
- proportioning device.
- prevents you from setting a hypoxia mixture with the flow control valves
- limits N2O flow to 3 time O2 flow 3:1 ratio (N2O max - 75%)
Annular space
The area between the widest area of the indicator field and side wall of flowmeter.
Thorpe tube
- traditional flowmeter.
- Is the beginning of the low pressure system.
which position of the O2 flowmeter minimizes the risk of a hypoxia mixture in the event of a flowmeter leak?
O2 flowmeter should be positioned all the way to the right (closest to the common gas outlet)
Reynolds Number
Predicts flow rate through a tube and determine when the gas flow is laminar or turbulent
Reynolds number = DensityxDiameterxvelocty/viscosity
Flowmeter FiO2 calculation
FiO2 =
Airflow rate x21)+(O2 flow rate x100
————————————-
Total flow rate
How to calculate tidal volume with fresh gas coupling
Total tidal volume =
Vt set on ventilator + FGF during inspiration - volume lost to compliance
Circuit compliance
Compliance =
Change in volume
————————-
Change in pressure
- it is a measure of distensiblity
- when the ventilator produces positive pressure inside the breathing circuit, some of the gas in circuit expand. This quantity of gas does not reach the pt.
Variable bypass vaporizer
- by setting the concentration dial, you determine the splitting ratio of fresh gas that enter vaporizer and the rest that bypasses the anesthetic liquid.
- These two fractions mix before leaving vaporizer and determine the final anesthetic concentration.
- gas that goes in the vaporizer becomes 100% saturated with agent.
- Flows less than 200mL/min or more than 15L/min can reduce vaporizer output.
How many pressure systems does an anesthesia machine have?
-3
- HIgh pressure
- intermediate pressure
- low pressure
What is included in the high pressure system of an anesthesia machine?
- Cylinders
- Hanger yoke
- Yoke block with check valves
- Cylinder pressure gauge
- Cylinder pressure regulator
What is cylinder supply used for?
- emergency use only
- tanks should only be open when checked or when pipeline supply is unavailable
How many psi are in the following compressed gas cylinders?
- oxygen
- carbon dioxide
- nitrous oxide
- air
- oxygen: 1900-2200, capacity 660L
- Carbon dioxide: 745, capacity 1590L
- Nitrous oxide: 745, capacity 1600L
- Air: 1800, capacity 600L
What is the PISS
- Pin Index Safety System
- method to prevent misconnections
- each cylinder valve has a unique arrangement of pins that corresponds to its intended contents
- matches holes in the yoke
- can be defeated if pins are missing, are removed, or if more than one washer is used
What is the cylinder valve?
- most fragile part of the cylinder
- contains PISS pins
- if fire/increased temp causes pressure in cylinder too increase, safety relief devices release contents in controlled fashion
What is safety relief devises of Cylinder valve?
- fusible plug made of woods metal
- frangible (fragile) disc that bursts under pressure.
- valve that opens under extreme pressure
What is hanger yoke?
- orients the cylinder
- ensures unidirectional flow
- contains a filter required by standard
- check valve to minimize transfixing
What is included in the intermediate pressure system?
- 40-50psi
- ventilator power inlet
- pipeline inlet
- check valves
- flow meter valves
- oxygen pressure-failure devices
- oxygen second stage regular
- flush valve
What problems can occur with pipeline supply?
-pressure loss or excess pressure
-cross-connection of gas delivery pipeline
-leaks
Theft of nitrous oxide
What do you do if oxygen pipeline failure?
- do not attempt to fix O2 analyzer
- turn on backup oxygen cylinder and disconnect pipeline
- use low flow oxygen
- turn off ventilator and bag manually
- call for help and calculate time remaining on cylinder
- do not reconnect pt to pipeline until tested
- ventilate with an oxygen source or room air via bag valve mask
What are the 5 tasks of oxygen in the AGM?
- proceed to the fresh gas flowmeter
- powers the oxygen flush
- activates the fail safe device
- activates the oxygen low pressure alarm
- compresses the bellows of mechanical ventilation (does not do this if they have piston)
What devices (or techniques) do not rely on wall outlet power?
- spontaneous or manually assisted ventilation
- mechanical flowmeters
- scavenging
- variable bypass vaporizers
What devices rely on wall outlet power?
- mechanical ventilators
- electronic monitors
- digital flowmeter displays
- vaporizers with electronic controls
How many pressure systems are in an anesthesia machine?
3
- high pressure
- intermediate pressure
- low pressure
What is the high pressure system?
-750-2200 psi
- cylinders
- hanger yoke
- yoke block with check valves
- cylinder pressure gauge
- Cylinder pressure regulator
What is cylinder supply used for?
- on reserve for an emergency
- tanks opened only when they are checked or when the spilling supply is unavailable
What are the pressures of compressed gas cylinders?
Oxygen:
- 1900-2200 psi
- 660L capacity
Nitrous oxide:
- 745 psi
- 1600L capacity
Air:
- 1800 psi
- 600L capacity
What is the Pin Index Safety System?
-PISS
-each cylinder valve has a uniqueness arrangement of pins that corresponds to its intended contents
-The pin arrangement matches holes in the yoke
where cylinders are attached to the gas machine.
-The PISS is a method to prevent misconnections.
-System can be defeated if the pins are missing, are
removed, or if more than one washer is used.
What is the cylinder valve?
-The cylinder valve is the most fragile part of the
cylinder and must be protected during transport.
-The cylinder valve consists of a body, the port
where gas exits, a conical depression for the
securing screw, PISS pins, and safety relief devices.
-If a fire causes the temperature and pressure
within the cylinder to increase, safety relief devices
release cylinder contents in a controlled fashion,
rather than explosively.
What are the safety relief devices of cylinder valves?
-Frangible disc that bursts under pressure
-Valve that opens under extreme pressure
-Fusible plug made of Wood’s metal
What is the hanger yoke?
-Orients the cylinder -Provides a gas tight seal -Ensures unidirectional flow -Contains a filter required by standard -Check valve to minimize transfilling
What is the Intermediate Pressure System?
40-50 psi
- Ventilator power inlet
- Pipeline inlet
- Check valves
- Pressure gauges
- Flow meter valves
- Oxygen pressure-failure devices
- Oxygen second stage regulator
- Flush valve
What is the Pipeline supply?
-Oxygen is produced by the fractional distillation of
liquid air. It is delivered to the hospital and stored
as a liquid, at 184*C.
-Various components convert the liquid oxygen to a
gas and supply it to the hospital pipeline at 50 psi.
(344kPa)
-Shutoff valves are present in the OR suite to isolate
leaks and interrupt supply in case of fire.
What are some problems with pipeline supply?
- Pressure loss or excess pressure
- Cross-connection of gas delivery pipelines
- Contamination
- Leaks
- Theft of nitrous oxide
What happens during loss of pipeline supply?
-Loss of oxygen pipeline pressure is indicated by
the pipeline pressure gauge.
-If pressure loss is profound, the oxygen low-
pressure alarm sounds, and the fail-safe valves halt
the delivery of all other gases.
What are guidelines for oxygen pipeline supply failure?
- Do not attempt to fix the oxygen analyzer. It must be trusted until proven inaccurate.
- Turn on backup oxygen cylinder on machine fully, and disconnect pipeline. If inspired 02 does not increase, ventilate by bag mask.
- Use low flow of oxygen.
- Turn off ventilator and bag manually.
- Call for help, calculate the time remaining on the cylinder.
- Find out details of problem and how long.
- DO NOT reconnect patient to pipeline unless it is tested.
- Ventilate with an oxygen source or room air via bag valve mask.
What are the 5 talks of oxygen in the AGM?
- Proceeds to the fresh gas flowmeter
- Powers the oxygen flush
- Activates the fail safe device
- Activates oxygen low-pressure alarm
- Compresses the bellows of mechanical ventilators
What are the 3 primary valves of the AGM?
- free-floating valves
- ball and spring valve
- diaphragm valve
What are free-floating valves?
- move in the direction or “push” of gas flow
- prevents gas from leaking out of the system
- found in DISS and dual hanger yoke systems
AKA: check valve
What are ball and spring valves?
Fail-safe valve
-used to prevent giving nitrous with out oxygen (oxygen opens valve)
Also in the oxygen flush?
What are diaphragm valves?
- only 2 of these in machine
- First stage regulator (between cylinder and intermediate pressure)
- Second state regulator (between intermediate pressure and low pressure)
*all they do is reduce pressure
What is the low pressure system?
- 16 psi
- flow meter tubes
- vaporizers
- check valves
- common gas outlet
What is the proportioning system?
- hypoxic guard
- safety device for flow meters. As turn on nitrous, oxygen will go on
What are Anesthesia gas vaporizers?
- agent specific vaporizer
- variable bypass vaporizer
- introduces anesthetic gas.
- cant’ mix between vaporizers
What is the copper kettle?
- vaporizer no longer used
- measured flow vaporizer
What are modern anesthesia gas vaporizers?
-Deliver a constant concentration of agent regardless of temperature change or flow through vaporizer.
-Temperature compensation is achieved by a strip composed of two different metals welded together. The metal strips expand and contract differently in response to temperature changes.
What are the different “delivery” breathing systems?
Open System
Semi-Open System
Semi-Closed System
Closed System
What is the open system?
- open system. = no mask on face
- No dead space
- Anesthetic to patient by insufflation
- Room air inhaled and anesthetic diluted
- Limited use in current practice ~ pediatric induction
- No breathing bag or reservoir bag
- No valves
*nothing to control which way air is moving
What is the semi-open system?
*semi-open = mask on
-Placed over face and patient spontaneously breathes inhaling anesthetic and room air (open drop technique) —_Carbon dioxide accumulates under mask, oxygen concentration would
decrease to below healthy level.
-Reservoir bag, no rebreathing
-Room pollution
-High gas flows
-Unidirectional valve
-Increased resistance
-Valve may malfunction
*control what they breath in, but what they breath out goes into the air
What does the pethick test for the Bain circuit check for?
Tests the low-pressure system and the integrity of the inner tube
*chance of FGI being blocked, this test make sure System is working
What is semi-closed system?
- semi-closed = mask on face
- what we typically use
-Anesthetic gas remains in the system
-No room air inspired
-Expired gas exits system through scavenging system, CO2
absorber
-Gases are in delivered flow to inspiratory site
-Unidirectional valves, one inspiratory and one expiratory
-Reservoir bag with a capacity of about 6 liters/minute
-Conserves moisture and heat
-Fresh gas flow can be less than patient’s minute volume
-Consists of:
-Pop off valve
-Corrugated tubing (22mm)
How is carbon dioxide neurtralized?
Use of either soda lime or barium hydroxide lime
-can tell in needs changed by violet indicator
What is an HME?
Heat and moisture exchanger
- Help to retain heat and moisture with the anesthesia circuit
- they all act as large particle filter and many serve as effective bacterial and viral filters
What are advantages of HME?
- No need for water or electrical power source
- No risk of hyperthermia
- No risk of overhydration
- No risk of burns
- No risk of electrical shock.
What are disadvantages of HME?
-The primary disadvantages of HMEs are that they are not nearly as effective at warming and humidifying the patient’s airway as water-based, electrical devices.
-They also increase deadspace and can increase the work of breathing.
-Airway obstruction can occur if the HME becomes blocked with fluid, blood, secretions, nebulized drugs
-If increased airway resistance is experienced during an anesthetic, the peak pressure should be measured both with and without the HME in place to assess for a mechanical defect is present in the device.
What are the 2 types of HMEs?
- Hydrophobic
- Hygroscopic
- resistance only increases slightly when wet
- more effective at preserving heat and humidity
What is a closed system?
*closed = mask on face
-Anesthetic agents are contained in the system and
are not vented
-Rebreathing of all gases ~ pop off closed (less
pollution)
-Carbon dioxide absorber in system to neutralize CO2
-Unidirectional valves
-Flow 150-500 ml/min for physiologic requirements
-Flow 150-250 ml/min under anesthesia
-Unknown gas concentrations
What is the basic anesthesia ventilator design?
-Automates the process of manual ventilation.
-Manual switch is moved, directing exhaled gas flow to the
bag (manual ventilation) or ventilator (automated ventilation).
- Bellows is used to separate the drive gas from the patient gas.
- Pneumatic powered – regulated, high pressure supply gas is used to move bellows.
-Produces desired inhalation and expiration.
What are the modes of modern gas driven bellows ventilator ?
-Manual/Spontaneous
-Volume-controlled ventilation (VCV)
-Pressure-controlled ventilation (PCV)
-Synchronized intermittent mandatory ventilation (SIMV)
-With/without pressure support of spontaneous breaths
What is the driving mechanism of a bellows ventilator?
-force of compressed air or O2
What is the ventilator relief valve?
-Spill valve or overflow valve
-Remains open during expiratory phase
-Prevents buildup of volume and pressure within the
breathing circuit
-During inspiratory phase, driving gas closes this relief valve, preventing gas within the bellows from exiting to scavenger.
-During early expiration, a weight within the ventilator
relief valve holds the pathway closed until the bellows
have filled.
-This creates a small amount of PEEP that is inherent to
the bellows design. (2-3 cmH2O)
What are modern piston driven ventilators?
-Use electric motor to compress the gas in a rigid
piston during the inspiratory phase of respiration.
-Do not require a drive gas.
-Do not deplete the O2 cylinder in case of pipeline O2 failure.
-Safe and effective
-Out of anesthetists field of view
-Has built in positive and negative pressure release valves.
What are advantages of modern piston Drive ventilators?
-Quiet -No PEEP -Precision of tidal volume -System controlled leak and compliance compensation -Fresh gas decoupling
What is fresh gas decoupling?
-fresh gas flow during inspiration is delivered to the manual breathing bag
What are disadvantages of the modern piston driven ventilator?
-Loss of visibility
-Quiet
-Does not easily accommodate non-rebreathing systems
-Potential for NEEP
-Potential to dilute patient’s inspired gas concentration with room air.
How to respond to sustained high pressure in breathing in circuit?
-Switch to “bag mode” or manual ventilation
-Try manually ventilating the patient
-Assess and treat patient related causes…. __________________.
-If circuit pressure is sustained during manual ventilation
-Scavenger obstructed
-Scavenger relief valves have failed
-Disconnect scavenging system if possible
-Use Ambu bag to ventilate patient
-If circuit pressure is relieved after removing ventilator from system
-Ventilator relief valve is malfunctioning
-Ventilator must be repaired and is NOT TO BE USED!!
What is volume control ventilation?
Delivers a constant tidal volume with each breath. Pressure will vary with changes in lung compliance and resistance.
What is pressure control ventilation?
Delivers a constant inspiratory pressure with each breath. Volume will vary with changes in lung volume and compliance.
What is synchronized intermittent mandatory ventilation?
VCV or PCV breaths are provided at the preset respiratory rate. Spontaneous efforts can trigger these breaths. Spontaneous breaths that exceed the preset rate rigger PSV breaths
What is pressure support ventilation?
Detects inspiration and augments spontaneous breath by adding preset pressure during inspiration. Can also provide a set amount of expiratory pressure (PEEP).
What is the scavenging system?
-Receives wast gas from the AGM (APL) and the ventilator.
How do you avoid waste gas exposure?
-Good mask fit
-Avoid unscavengeable techniques if possible (insufflation) -Prevent flow from breathing system into room air (only turn on agent and nitrous oxide after mask is on face, turn them off before suctioning)
-Washout anesthetics (into the breathing circuit) at the end of the
anesthetic
-Don’t spill liquid agent Use low flows Use cuffed tracheal tubes when possible
-Check the machine regularly for leaks Disconnect nitrous oxide pipeline connection at wall at the day’s end (beginning?)
-Total intravenous anesthesia
What are the 5 tasks of oxygen in the anesthesia machine?
- O2 pressure failure alarm
- O2 pressure failure device (failsafe)
- O2 flowmeter
- O2 flush valve
- Ventilator drive gas (a piston driven ventilator does not require this)
What is the DISS?
- Diameter Index Safety System
- prevents inadvertent misconnections of gas hoses
How much anesthetic vapor is produced by 1mL of liquid anesthetic?
200mL of anesthetic vapor
Is the vaporizer in circuit or out of circuit?
Out of circuit
What is the most common cause of a vaporizer leak?
Loose filler cap
A leak can only be detected when the vaporizer is turned on
How do you calculate how much liquid anesthetic is used?
-mL of liquid anesthetic used per hour = vol% x FGF(L/min) x3
What is the only vaporizer that is not a variable bypass vaporizer?
Tec 6 and Draper d-vapor
- only vaporizers approved for use of desflurane
- this is bc des is significantly less potent and has a vapor pressure close to atmospheric pressure. It’s vapor pressure is 3-4x higher than other agents
-this vaporizer does not compensate for changes in elevation. A lower pressure (higher altitude) requires a higher setting on dial
What is the oxygen analyzer?
- monitors O2 concentration, not pressure
- can detect an oxygen pipeline crossover
- it can detect a leak in the breathing circuit
What are the 3 types of ventilators used on anesthesia machines?
- ascending pneumatic bellow
- descending or hanging pneumatic bellow
- piston
What happens to the breathing bag during during inspiration and exhalation
- inflates during inspiration
- deflates during expiration
