Week 1: Anesthesia Machine Flashcards
Defined as a gas that does not liquefy at ambient temperatures, regardless of the pressure applied.
Non-liquified, compressed gas
Examples of non-liquified, compressed gas
Oxygen (O2)
Nitrogen
Air
Helium
A gas that is a liquid at ambient temperatures and pressures between 25 - 1500 psi.
Liquified, compressed gas
Example of liquified, compressed gas:
Nitrous Oxide (N2O) - Liquid at room air.
Enforce the purity of medical gases
FDA - Food and Drug Administration
They publish requirements for the manufacturing, marking, labeling, filling, qualification, transportation, storage, handling, maintenance, and disposition of medical gases.
Department of Transportation (DOT)
Regulate matters affecting the safety and health of employees
Department of Labor (DOL)
&
Occupational Safety and Health Administration (OSHA)
Published standards that are voluntary
National Fire Protection Association (NFPA)
And
Compressed Gas Association (CGA)
Cylinders range in sizes from ____ to ______
A to H
Cylinders ____ to _____ utilize a pin-index safety system (PISS) to decrease chances of misconnections and delivery of hypoxic mixtures
A to E
(All cylinders are also color-coded as a safety measure).
The ______ marking indicates aluminum. * this cylinder is used in the MRI environment.
3AL
The ______ marking on a cylinder indicates steel
3AA
*most tanks are constructed of steel
The _____ of a cylinder attaches to the valve. It contains the: 1.____ 2._____
NECK
- Pressure regulators 2. Flow-metering device
This is where cylinders are filled and discharged.
The VALVE
- made of bronze or brass
- attached to the neck
Where the gas exits from the cylinder.
The Port.
*it should be covered in transit.
* do not mistaken the port for the depression on the other side of the valve.
Rotated to open or close the valve. When turned counterclockwise it ______ the valve and clockwise it _________ the valve.
The Stem
Opens ; closes
When the valve is open, the stem moves ________ allowing gas to flow to the port.
Upward
On a cylinder: When the handle is turned clockwise it pushes the _______ downward and closes the seat. This prevents leakage of the gas.
Upon opening the valve, the upward force of the spring opens the seat.
Diaphragm
- The diaphragm valve is preferred in the cylinders because no leaks can be allowed with flammable gases.
Packed valve
Prevents leakage of the gas.
*small cylinders: stem sealed with teflon.
*large cylinders: force is transmitted by means of a driver square capable of withstanding high pressures.
Usually attached to the anesthesia machine. Used to close or open the cylinder valve:
The Handle
*It causes the stem to turn allowing gas to flow out of the port.
What do Pressure Relief Devices do?
They will vent the cylinder contents to the atmosphere if the temperature of the enclosed gas increases to a dangerous level.
Types of pressure relief devices:
Rupture disc, Fusible plug, and Pressure Relief Valve.
It protects against excess pressure as a result of high temperature or overfilling. When a predetermined pressure is reached, the _________ breaks and allows ALL the contents inside cylinder to be released.
The Rupture Disc
- follows the Gay-Lussac’s Law: Increase in Temp = Increase in Pressure.
*a metal disk designed to break off at high internal pressure
(AKA - frangible disk assembly).
This pressure relief device will only protect from excessive pressure caused by a high temperature. It is thermally operated.
Fusible Plug
* has low melting point, will melt in a fire and allows all the gas to escape.
A spring-loaded device that will close once once normal pressure has been restored in the cylinder
Pressure relief valve
AKA - safety relief valve.
*the set pressure at which a cylinder will discharge is marked on the valve.
*found on air, helium, oxygen, nitrogen, and carbon dioxide cylinder. (- NOT on N2O)
Relies on two stainless steel pins on the cylinder yoke connector just below the fitting for the valve outlet port. These pins fit exactly into the corresponding holes in the cylinder valve positioned in an arc.
Pin Index Safety System (PISS)
*designed to ensure that the correct gas is connected to its corresponding CYLINDER yoke.
*7 combinations are possible.
NON-INTERCHANGEABLE SYSTEM.
PISS connections for
AIR:
OXYGEN:
NITROUS OXIDE:
Nitrogen:
Air: 1, 5
Oxygen: 2, 5
Nitrous Oxide: 3, 5
Nitrogen: 1,4
Tank color of gases:
Air -
O2 -
N2O-
Helium-
CO2-
Nitrogen-
- Suction * -
Air - yellow
O2 - green
N2O- blue
Helium- brown
CO2- gray
Nitrogen- black
Suction- white or purple
How much pressure should oxygen tank should have least before starting a case?
1000 psi (Half-filled tank)
The most common size cylinder used in anesthesia.
Size E
*A is the smallest and H the largest.
*volume and pressure of a gas in a particular size cylinder may vary.
O2 gas E- cylinder psi and liters:
2000 psi
660 L
Nitrous Oxide (N2O) E- cylinder psi and liters.
1590 Liters
745 psi
Air E- cylinder psi and liters:
625 L
1900 psi
Can you know how much volume is left based on the pressure O2 tank?
Yes, the pressure in an oxygen tank is proportional to the volume of oxygen in the cylinder.
Ex. 500 psi = 1/4 of the total volume (660L) = about 155L
Can you know how much volume is left based on the pressure of N2O?
No, the pressure depends on the vapor pressure of the liquid and is not an indication of the amount of gas remaining in the cylinder.
The pressure gauge remains at 745 psi as long as there is some liquid in it.
When all liquid is evaporated, the pressure will decline.
How can the volume of an N2O tank be determined?
By weighting the actual cylinder.
At the point where the liquid in an N2O cylinder and the pressure gauge drops the container is more than ________ empty.
3/4 (75% empty = so about 400L. Full tank is 1590L).
When calculating how long the O2 will last, the calculation refers only to requirements at the __________ and assumes ___________.
Flowmeters; manual ventilation
The tanks are permanently stamped on the __________ of the cylinder. And the test _______ should also be placed on the cylinder.
Shoulder ; Date
The diamond-shaped figure on a cylinder denotes the:
Hazard class (flammable or non-flammable).
Each cylinder should have a white label with:
- The name of gas
- Hazard class
- Expiration date
- Name and address of expiration.
Each cylinder should have a tag that indicates:
FULL, IN USE, or EMPTY
What is an oxidizing gas?
Ones that has oxygen in it. O2 and N2O are both oxidizing gases. They are flammable
Cylinder Hazards
- incorrect cylinder
- incorrect contents
- incorrect valve
- incorrect color
- incorrect labeling
- damaged valve : may cause cylinder to have leak
- Fires: occurs if oxidizing agent present
- Explosion: a cylinder that it is incorrectly filled may not have the proper pressure relief device.
- projectile rocket: if a cylinder falls and the valve breaks. Small should be placed in rack and large should be chained to wall.
- N2O theft: people use it for substance abuse.
- Thermal injury : frost bite from people who use it recreationally.
-Blocked flow meter: if integrated, O2 will not flow.
A pressure regulator in the central supply, normally pipes the gases in at ____ to _____ psi into the anesthesia machine.
50 to 55
The anesthesia machines pull the gas from the _______ pressure source.
Highest
- close O2 tank because pipeline pressure may fluctuate and machine will take the gas from the tank.
Oxygen is stored in the central supply as ________, below its ________, where the potential for ignition is decreased.
Liquid; Boiling point.
Boiling point of Oxygen (O2)
- 297.3 F (-182.9C)
N2O is stored as _______. The problem with N2O cylinders is that the regulator may become so cold it freezes. A warning sign where these are stored should be place because it could create a ____________.
LIQUID ; Hypoxic mixture.
Safety system used in the PIPELINE system to prevent improper connection of supply hoses. *DOES NOT PREVENT HYPOXIC GAS MIXTURE from being delivered to patient.
Diameter Index Safety System (DISS)
- Connection points are gas specific, NON-interchangeable.
- This system is always on the anesthesia machine for pipelines.
DISS connector consist of:
Body, nipple and nut combination.
The 2 most important things you need when changing out a cylinder tank:
A washer (Bodok seal) - prevent leaks
And the handle ( to open/ close tank).
Quick-coupler WALL connections for pipelines have:
Two- prominences on the hose
In the event of pipeline crossover, two actions must be taken:
- The back up oxygen must be turned on (since it’s always off).
- The pipeline supply sources must be disconnected. MANDATORY because the machine will preferentially use the 50 psi pipeline supply source instead of the lower-pressure 45 psi.
Do not let someone plug a ___________ in your anesthesia machine.
Bair Hugger
Basic Components of the Anesthesia Workstation:
- Gas inlets (back of machine)
- Pressure regulators
- Oxygen- pressure failure devices
- Flow-control valves and flowmeters
- Vaporizers
- Fresh gas outlet
- Spirometers
- Breathing circuit
- Pressure gauge
- Ventilator
- Scavenger
- Oxygen analyzer
Consist of those parts that receive gas at cylinder pressure (45 to 2000 psi), this includes cylinder gas down regulated by a first stage regulator.
High Pressure System
High pressure system consist of:
Hanger yoke
Hanger yoke check valve
Cylinder pressure regulator (first-stage)
Cylinder pressure gauge
Receives gases at relatively low and constant pressures of 30 - 55 psi (pipeline pressures)
Intermediate pressure system
Intermediate pressure system includes
- pipeline inlets and pressure gauges
- ventilator power outlet accessory
- O2 flush valve
- Supply failure alarm system
- Oxygen failure safety valve
- Second stage pressure regulator
- Flowmeter VALVES
All parts receiving gas from either a pipeline or cylinder air 15 - 30 psi. The second stage regulator drops pressures from intermediate to low pressures to low pressures, and allows for SAFE DELIVERY OF GASES TO PATIENTS.
Low pressure System (LPC)
Low pressure system includes:
- Flowmeter TUBES
- Vaporizers
- Temperature compensating bypass valve
- Common gas outlet
The LPC leak test checks the integrity of the anesthesia machine from the ______________ to the ______________.
Flow control valves to the common gas outlet.
The most delicate pneumatic component of the anesthesia machine:
Flow tubes
*they can crack or break
Leaks in the LPC can cause:
Hypoxia or subanesthetic mixture;
*leading to a hypoxia injury or patient awareness
The LPC is the most _________ area of the anesthesia workstation
Vulnerable
- most subject to breakages and leaks. Also most likely to go unrecognized if an LPC leak test is not done.
The leak test should be done :
Each day or when a vaporizer is changed.
If a machine has a one-way check valve (outlet check valve) should a positive or negative leak test be done?
Negative- pressure leak test should be done.
*a positive- pressure test will not detect leaks in the LPC of machines with an outlet check valve.
The LPC evaluates the portion of the machine downstream from all safety devices except the:
Oxygen analyzer
Usually made of steel, but made be made of aluminum
Body of cylinder
Attached to the neck of the cylinder, used for filling and discharging, may be made of bronze or brass, and regulates pressure down.
The cylinder valve
Point of exit for gas, usually covered until cracked.
The cylinder port
Within the valve, closes the valve by sealing against the seat, and when opened, it moves it upward and away from the seat.
The Stem of the cylinder
Cylinders are tested every 5 years unless exempted for :
10 years.
Cylinder Hanger Yoke
the attachment on the anesthesia machine where the cylinders are set into place.
The cylinder hanger yoke contains:
Body retaining screw
Nipple
PISS
Washer
Check valve (to prevent back flow into the cylinders).
High pressure cylinder gauges measure:
Measures pressures within a given cylinder
*Bourdon type gauge
The Bourdon Gauge consist of a closed coiled tube connected to the cylinder in which pressured is to be sensed. As the pressure increases the tube will ________, while a reduced pressure will allow tube to ____________. This motion is transferred through a link to a gear connected to an indicating needle.
UNCOIL when pressure up.
COIL more tightly when pressure down.
Controls the variable pressure inside a cylinder. Reduce the high pressure in a cylinder to ~ 45 psi.
High pressure regulator
When you connect the oxygen source (either tank or pipeline) to the anesthesia machine, 5 immediate functions occur or are activated:
- The power outlet accessory
- O2 flush valve is activated
- Pressure sensor shut-off valve (fail-safe valve)
- Supply failure alarm system
- Second stage pressure regulator
Provides pressure to the ventilator
Power outlet accessory
*usually powered by oxygen coming from pipeline.
O2 flush valve delivers oxygen at what pressure and L/min?
At ~50 psi and 35-75L/min
*NEVER USE THIS WHEN CIRCUIT CONNECTED TO A PATIENT
- Bypasses second-stage regulator
How those the pressure sensor shut-off valve work? (Fail-safe valve)
When O2 supplied at ~50 psi, this valve remains in the open position allowing N2O to flow to the Flowmeter
It remains open as long as PSI remains >25. If it falls below 25 psi, then N2O flow is shut-off.
**ONLY RESPONDS TO PRESSURE.
Activated when O2 falls below 28 psi.
Second stage pressure regulator
*Alarm sounds before 25 psi, the point at which N2O flow will cease.
Gas pressure is decreased by a ____________ to a CONSTANT pressure of 16 psi because the flow from the wall (pipeline) varies at times between 40 - 50 psi.
Second stage pressure regulator (12-19 psi in Barash).
*after passing 2nd stage pressure regulator, the gas sits in “stand by” at flow control valve.
Include all parts of the machine which receive gases at reduced pressure from cylinders (35-45 psi)
Intermediate pressure system
**Starts after the first stage regulator when cylinder gases used.
** includes pipeline gas inlets and pressure gauges (deliver gas at 50psi), oxygen failure safety valve and oxygen supply failure alarm, flow VALVES, and oxygen flush valve.
Oxygen failure cutoff valves do not prevent delivery of hypoxic mixture. (T or F)
True. Delivery of hypoxic gas may still occur.
All open or all closed system
O2 pressure-sensor shut off
Oxygen proportioning device creates a minimum FIO2 of ________. A N2O (26 psi) : O2 (14 psi) ratio of _______.
25%.
Ration of 3:1
- it ensures that nitrous oxide can only be delivered in the presence of O2 to the patient.
Turning N2O will make O2 follow. If O2 is decreased - N2O will follow.
* If N2O is turned off - O2 will not necessarily follow.
The anesthesia machine is always running O2 anywhere from _______ to _______, even when machine is completely off.
200 - 300 ml/min (Anesthesia machine book)
50 - 150 ml/min (on PowerPoint)
(Cross said: 0.1 - 0.25 L/min )
The oxygen knob is _______, versus “________,” larger than the other, and protrudes further out.
FLUTED ; gnarled.
*OXYGEN LOCATED ALWAYS furthest to the RIGHT.
Oxygen flush valve bypasses flow meters and vaporizers and goes directly into the CGO at _______ psi and _________ L/min.
35- 75 L/min
~ 45 to 55 psi.
O2 flush valve used for:
- used to rapidly refill or flush the breathing circuit
**NEVER while pt connected. - may cause barotrauma.
Variable-orifice flowmeters are _______ pressure and use an indicator ball (or bobbin) which displays the flow of gas through a ______ tube.
Constant-Pressure ; Thorpe tube
*tube is narrow at the bottom and low flow raises the marker. As the flows increase and the marker rises in the widened tube, greater flows pass around it and reach the CGO.
*may be single or double tube design.
Flowmeters floats should rotate freely, inside of tubes is coated to prevent:
Static electricity
In the flowmeters: if a leak occurs it can:
Cause a hypoxic gas mixture
Flow into the meters moves from the _____ to the ______, exiting the common manifold to the right of the O2 Flowmeter.
Left to Right
- If there is a leak in the first two flowmeters - oxygen continues uninterrupted out to the patient. - O2 IS ALWAYS DOWNSTREAM.
- A leak in O2 Flowmeter or beyond may cause a hypoxic mixture
What is a volatile agent?
an anesthetic agent which exists as a liquid at room temperature and evaporates easily for administration by inhalation.
All fresh gas flow (FGF) enters the _______, the more you put in the more quicker the _______ will burn out.
Vaporizer x2
The number of calories required at a specific temperature to convert 1 G of liquid to vapor.
Heat of Vaporization
Internal vaporizers leaks can only be detected with vaporizer turned to the “on” position. In the “off” position the vaporizer is excluded from the:
Low - Pressure Circuit (LPC)
Modern vaporizers are agent specific. Precisely calibrated and constructed with metals with _____________ conductivity.
High -thermal.
*it allows the heat to flow from the vaporizer into the anesthetic in the liquid phase, supplying the energy for the heat of vaporization.
Temperature compensating bypass valve
Changes in the temperature are constant (room & cooling due to vaporization - endothermic reaction). The bypass valve will open and allow gas to bypass vaporizer chamber depending on temp.
Do not tilt vaporizer beyond _____ degrees. If it is tilted what should be done?
45 degrees.
- the vaporizer must be drained and dried; otherwise it can deliver uncertain % of anesthetic agent.
Vaporizer interlock system ensures that:
One one vaporizer is turned on
**vaporizers are locked into the gas circuit, thus ensuring they are seated correctly.
What color is Halothane Agent?
Red
*not in practice
What color is isoflurane agent?
Purple
*super cheap. Turn off 40 - 30 mins before ending case. Hang on for a while on fat tissue
What color is sevoflurane agent?
Yellow
- most common safer
What color is enflurane agent?
Orange
What color is Desflurane agent?
Blue
*Need a lot to make someone asleep
*Very expensive and bad for O-ZONE
*patient can come off of it quickly
Higher vapor pressure (VP) agent in a Lower VP vaporizer will deliver:
High concentration.
( H L H )
Low VP agent in a Higher VP vaporizer chamber will deliver:
Low concentration
(L H L )
Ex: Sevoflurane in Desflurane vaporizer - concentration will be very low.
If wrong agent is put in wrong vaporizer:
Vaporizer must be emptied and flush with 100% O2 and dry.
Variable- bypass vaporizers lack
A external heat source
Tec 6 Vaporizers made specifically for:
Desflurane
The vapor pressure of Desflurane is 3-4x times higher than that of the other inhaled vaporizers. It boils at approximately _______ degrees C and its vapor pressure is _______.
22.8 ; 669 mmHg (near 1 atm) at 20C.
** Desflurane requires special vaporizer.
The Tec 6 vaporizer is ELECTRICALLY heated to approx. _______ degrees C.
39C
**if not heated, large amounts of Desflurane would be required 4-9x more.
** vaporizer gets hot.
Tec 6 vaporizer pressurizes Desflurane to ______ atm
~ 2 atm (~1500mmHg)
*control amount of Desflurane output.
Liquid anesthetics cool during vaporization, which in turn ________ the saturated vapor pressure.
Decreases (endothermic reaction)
**by using metals with high conductivity to build vaporizers rapid heat transfer to the anesthetic takes place, decreasing the effects of cooling.
In a vaporizer when temperature increases, the valve in the bypass opens wide to create a higher splitting ratio. More gas flows through the ________, and less gas enters the _________.
Bypass ; Vaporizer
** a smaller volume of a higher concentration of vapor emerges from the vaporizing chamber.
*when temperature decrease the reverse occurs.
Common gas outlet ( AKA ____________)
Fresh gas outlet.
Circle System includes
- Fresh gas inflow
- Unidirectional Valve
- Corrugated tubes
- Y-piece
- APL valve (pop-off valve or adjustable pressure relief valve).
- Reservoir bag
- CO2 absorbent
** NOT PART OF THE LPC
When manually ventilating keep APL valve < 20 to prevent:
Stomach insufflation
Static test - Leak test
Circle system is pressurized to 30-cm water pressure, and the circle system airway pressure gauge is observed.
Close APL valve (pop-off), occlude y-piece, and use O2 flush valve to pressurize.
** THIS DOES NOT CHECK INTEGRITY OF FUNCTIONAL VALVES.
Dynamic test - Flow test
To check for appropriate flow to rule out obstructions and faulty valves. Vent and reservoir bag are used.
The breathing system test and leak test should be done:
Before starting each case
Where gas from the common gas outlet enters the breathing circuit
Common gas inlet
It is part of the circle system when manually ventilating via bag; but it is bypassed when mechanical ventilator is in use
APL Valve
- Fully open = less pressure ( 0 )
- Fully closed = more pressure ( 70)
The breathing tubes and y-piece consists of ______ tubing. They are heated and humidified.
Corrugated
The inspiratory and expiratory ports are the place of attachment for the _____________ onto the machine
Breathing circuit
Reservoir bag for assisting manual ventilation come in different sizes:
1L , 2L, *3L (for adults)
The oxygen analyzer is the most important part of the anesthesia machine because it can detect a __________. And it is calibrated to _______.
Hypoxic mixture. 21% (room air)
*located distal to the CGO, as proximal to the patient as possible.
APL valve: usually fully ______ during spontaneous ventilation, but must be partially ________ during manual or assisted bag ventilation.
Open; Closed
Rebreathing of carbon dioxide may occur if either of the _______________ malfunctions.
Unidirectional Valve
- you want to see each valve flutter at the right time.
- expiratory valve is also exposed to moisture from the patient’s airway upon exhalation which could make it stick, increasing resistance.
If you only have one filter for the inhalation and exhalation ports, in which one should it be placed?
On the EXPIRATORY side.
*PROTECT ANESTHESIA MACHINE.
- what’s coming out of the machine should be clean to patient.
Carbon Dioxide Absorbent
- Allows for rebreathing of alveolar gas which CONSERVES heat and moisture.
Carbon dioxide absorbent ______ the need for higher flow of gases, since they can be recirculated.
Decrease
** Gases and anesthetic agents can be recirculated in an economical fashion.
CO2 absorber removes ___________ which has been exhaled by the patient.
Carbon dioxide
Component that allow the circle system to exist:
The CO2 Absorbent
During ___________ (only) anesthesia, compound A can be formed, particularly at _______ fresh gas flow (FGF) rates.
Sevoflurane; Low
Carbon MONOxide (CO) may be produced when volatile anesthetics are utilized, particularly with:
Desiccated absorbents
Desiccated __________ absorbents (particularly _______) can react with sevoflurane, producing extremely high absorber temperature and combustible decomposition products.
Strong base ; Baralyme
Baralyme (___________)
Barium hydroxide lime
** no longer available in the U.S.
CO2 absorbents:
- Soda Lime
- CaH Lime (Amsorb)
- Baralyme: no longer sold
CO2 absorbents chemical reaction end-products:
Heat, Water, and Calcium carbonate
Soda lime is most commonly used and _____ grams of absorbent can absorb _______ liters of CO2
100 grams ; 26 Liters
Size of CO2 absorbent granules: ____- mesh or _____- mesh.
4 or 8
** too small can lead to restriction of flow.
4- mesh is larger granules with less resistance but less surface area for CO2 absorption.
8 - mesh is smaller granules with larger surface area for absorption but more resistance.
During the weekend the anesthesia machine should be turned off to prevent the CO2 absorbents from
Drying out
How do you overcome a purple- CO2 absorbent if it can’t be changed in the middle of a case?
Increase your flows. If running 1L, increase 6-7 to overcome rebreathing.
Soda lime composed of
Calcium hydroxide (~80%)
Sodium hydroxide & potassium hydroxide (~15%)
Water (~5%)
Baralyme is composed of:
80% calcium hydroxide
20 % barium hydroxide
When ____ to ____% of the CO2 absorber granules have turned purple, the canister should be replaced.
50 to 70
Compound A
Fluoromethyl-2,2 - difuro-1- (trifluromethyl) vinyl ether
Factors increasing compound A
- Total gas flow rates below 1 L/min
- use of Baralyme rather than soda lime
- High absorbent temperatures
- High concentrations of sevoflurane
- Drying of the CO2 absorbent
- Length of anesthetic
Desflurane, enflurane, and isoflurane with absorbent produces ____________.
Carbon monoxide.
** higher concentrations with absorbers that have not been used for 24 hours or longer.
Factor that increase carbon monoxide CO:
- use of Baralyme rather than soda lime
- higher temperatures in absorber
- desiccated absorbent
- high anesthetic concentrations
- increase length of time.
For the oxygen analyzer, the oxygen concentration- sensing element ( usually a __________) must be exposed to room air (at sea level 1 atm) for calibration to 21%
Fuel- cell
At higher altitudes, the oxygen analyzer would read ____ than 21% even though the composition of the atmosphere is unchanged.
Less
Oxygen sensor may be ________ (Clark electrode), or ________ (fuel cell), these require calibration.
Polarographic ; Galvanic
Also known as respirometers, are used to measure the patient’s exhaled tidal volume.
Spirometers
** a rotating vane is present in the expiratory limb ; the flow of gas across the vanes causes them to rotate and the number of rotations/time is measured.
Humidifiers may be :
Active or passive
Passive humidifiers AKA: ___________ are most commonly used.
Heat and moisture exchangers (HME) or artificial noses
The provide an economical way of adding moisture to inhaled gases by trapping the moisture contained in exhaled gases; they conserve heat by the same means.
Passive humidifiers
They transmit nosocomial infections, cause thermal injury and increase airway resistance from excessive condensation.
Active humidifiers
When the bag/vent switch is turned to the ventilator mode, the breathing bag and APL are bypassed and the ventilator __________ replace their function.
BELLOWS
- Open APL valve while on ventilator (spontaneous).
The “PUMP” is either a ____________ to the ________ of the spontaneously breathing patient.
Mechanical ventilator ; Lungs
_________ and/or _______is the driving gas which allows the bellows to move up or down during ventilation
Oxygen or Air
Ventilators have a built-in pressure relief valve which allow the escape of gas if pressures reach a preset limit of
65 - 80 cm H2O
A __________ closes during inspiration so that positive pressure can be generated, and opens during expiration to prevent increased airway.
Spill valve
Ascending bellows ventilator _________ as the patient exhales; and descending bellows _________ as the patient exhales.
Rises; Drops
Ascending bellows provide positive pressure through the breathing circuit between
2-4 cm H2O of peep
Descending bellows: the weight of the bellows during expiration results in _______________ equal to the weight of the bellows.
Negative pressure
Which bellow is better - ascending or descending?
Ascending - because they will not rise again on expiration since pressure cannot built up in an accidental disconnection. Descending will continue to drop on expiration because of the weight.
Anesthesia machine ventilator power source:
Compressed gas, electricity or both.
Modern “piston ventilators” do to not require:
Driving gas
The bellows housed in a chamber separates the ___________ gases from ________ gas.
Breathing system; driving
Volume of gas entering or leaving the patient during the inspiratory or expiratory phase.
Tidal Volume
Sum of the tidal volumes in one minute
Minute volume
Number of respiratory cycles per minute
Ventilatory Frequency
The period between the beginning and end of inspiratory flow
Inspiratory flow time
Period from the end of inspiratory flow to the start of expiratory flow
Inspiratory pause time
period of time between the start of inspiratory flow and the beginning of expiratory flow, or it is the sum of the inspiratory flow time and the inspiratory pause time
Inspiratory phase time
Time between the beginning and end of expiratory flow
Expiratory flow time
interval from the end of expiratory flow to the start of inspiratory flow
Expiratory Pause time
time between the start of expiratory flow and the start of inspiratory flow or it is the sum of the expiratory flow time and the expiratory pause time
Expiratory phase time
is the ratio of inspiratory phase time to expiratory phase time
Inspiratory and expiratory phase time ratio: I:E ratio
volume of gas per unit time that passes from the patient connection of the breathing system to the patient
Inspiratory flow rate
volume of gas per unit time returned from the patient during the expiratory phase
Expiratory Flow Rate
pressure difference per unit flow across the airway; it usually increases as flow increases
Resistance
ratio of a change in volume to a change in pressure
Compliance
An initial tidal volume of __________ ml/kg of IDEAL body weight is generally indicated, with the lowest values recommended in the presence of obstructive disease and ARDs.
5-8
The goal is to adjust the tidal volume so that the plateau pressure are less than _______of water.
35 cm
A respiratory rate of _______ breaths per minute is recommended for adult patients not requiring hyperventilation for the treatment of toxic or metabolic acidosis or intracranial injury.
8 -12
High RR allows less time for __________, increases mean airway pressure, and causes air-trapping in patients with COPD.
Exhalation
Supplemental oxygen: The lowest FiO2 that produces an arterial oxygen saturation greater than ______ and a PaO2 greater than ______ mmHg is recommended.
90%; 60 mmHg
NO data indicate that prolonged use of an FiO2 less than 0.4 damages ____________.
Parenchymal cells
The normal I:E ratio to start is 1:2. This is decreased to ______ or _______ in the presence of COPD.
1:3 and 1:4
- Reduction of I:E helps avoid air-trapping and auto-PEEP.
Use of inverse I:E ratios may be appropriate in certain patients with complex compliance problems like:
ARDS
reduces the risk of atelectasis, trauma and increases the number of “open” alveoli participating in ventilation, thus minimizing V/Q mismatches
PEEP
Applying physiologic PEEP of 3-5 cm H2O is common to prevent decreases in ____________ in patients with normal lungs
Functional Residual Capacity
Inhalation proceeds until a set tidal volume is delivered and is followed by passive exhalation
Volume- Cycled Mode
- Gas is delivered with a constant inspiratory flow pattern, resulting in peak pressures applied to the airways higher than that required for lung distention (plateau pressure).
- Since the volume delivered is constant, applied airway pressures vary with changing pulmonary compliance (plateau pressure) and airway resistance (peak pressure).
A set peak inspiratory pressure (PIP) is applied, and the pressure difference between the ventilator and the lungs results in inflation until the peak pressure is attained and passive exhalation follows
Pressure- Cycled Mode
In the pressure-cycled mode: the delivered volume with each respiration is dependent on the ________ and _________ compliance.
pulmonary and thoracic
Breaths are delivered at preset intervals, regardless of patient effort.
Continuous Mandatory Ventilation
- Many ventilators do not have a true CMV mode and offer A/C instead
This mode is used most often in the paralyzed or apneic patient because it can increase the work of breathing if respiratory effort is present
Continuous Mandatory Ventilation
- Continuous mandatory ventilation (CMV) has given way to assist-control (A/C) mode because A/C with the apneic patient is equivalent to CMV.
The ventilator delivers preset breaths in coordination with the respiratory effort of the patient.
Assist Control Ventilation
- With each inspiratory effort, the ventilator delivers a full assisted tidal volume.
With each inspiratory effort, the ventilator delivers a full assisted tidal volume.
Assist Control Ventilation
As might be expected, this mode is better tolerated than CMV in patients with intact respiratory effort.
Assist Control Ventilation
breaths are delivered at a preset interval, and spontaneous breathing is allowed between ventilator-administered breaths
Intermittent mandatory ventilation (IMV),
Spontaneous breathing occurs against the resistance of the airway tubing and ventilator valves, which may be formidable.
Intermittent Mandatory Ventilation
The ventilator delivers preset breaths in coordination with the respiratory effort of the patient
Spontaneous breathing is allowed between breaths.
Synchronous Intermittent Mandatory Ventilation
Synchronization attempts to limit barotrauma that may occur with IMV when a preset breath is delivered to a patient who is already maximally inhaled (breath stacking) or is forcefully exhaling
Synchronous Intermittent Mandatory Ventilation
a full support mode in that the ventilator performs most, if not all, of the work of breathing.
This mode is beneficial for patients who require a high minute ventilation.
reduces oxygen consumption and CO2 production of the respiratory muscles.
A/C Ventilation
A potential drawback of A/C ventilation in the patient with obstructive airway disease is worsening of:
air trapping and breath stacking.
For the spontaneously breathing patient, has been advocated to limit barotrauma and to decrease the work of breathing
Pressure Support Ventilation
differs from A/C and IMV in that a level of support pressure is set (not TV) to assist every spontaneous effort.
Pressure Support Ventilation
It can result in improved patient comfort, reduced cardiovascular effects, reduced risk of barotrauma, and improved distribution of gas
Pressure Support Ventilation
New mode in which the ventilator operates as PCV, but a tidal volume target is also set
Pressure Control with Volume Guarantee
Initial vent settings suggestion
RR = 10 (8-12 adults)
TV = 500 (7ml per kg ideal body weight)
I:E ratio = 1: 2 (if COPD, then 1:3)
Pressure support = 10
Peep = 5
Provide a way for waste anesthetic gases (WAGs) to be removed from the breathing circuit via either the APL valve or the ventilator spill valve and out of the OR
Scavenger System
Scavenger hoses diameter
19 or 30 mm
Breathing hoses diameter
22 mm
When nitrous is used with oxygen, its maximum allowable limit is
25 ppm
When a halogenated agent is used alone with oxygen, its allowable limit is:
2 ppm
If a halogenated agent is used in the presence of nitrous oxide, the allowable limit for the halogenated agent is decreased to:
0.5 ppm
This type of system usually employs a closed scavenging interface since the waste gases are exiting at a passive rate; basically they are exiting the system as quickly as they are added to the system
Passive Scavenging
This requires an open scavenging interface to decrease the likelihood of creating negative pressure in the breathing circuit, or allowing pressures to increase to dangerous levels
• May use closed interfaces with valves (better)
Active Scavenging
An FDA approved, complete anesthesia machine checkout should be completed every:
Morning prior to the first case
What components does the Mapleson system incorporates?
- Breathing tube
- Fresh gas inlet
- Adjustable pressure-limiting (APL) valves
- Reservoir bag
Gases enter the mapleson circuit via the:
Fresh gas inlet
The position of the ________________ is the KEY DIFFERENCE among mapleson circuits.
Fresh gas inlet
Partial closure of APL valves limits gas exit; permitting ___________________ during reservoir bag compressions.
Positive circuit pressure
Functions as a reservoir of anesthetic gas and method of generating positive-pressure ventilation
Reservoir Bag
Mapleson circuit disadvantages
- High FGF to prevent rebreathing of CO2 result in waste of anesthetic agents
- pollution of the OR
- Loss of patient heat and humidity
Best mapleson circuit for spontaneous breathing
Mapleson A
Best mapleson circuit for controlled breathing:
Mapleson D : Bains System
