Exam 2 Flashcards
What are most gauges calibrated for?
Atmospheric pressure
What does non-liquified vs liquefied compress gas give us?
the relationship between pressure and remaining volume and pressure reading on the gauge
What do we apply to liquify a gas?
apply a low temp
Which gases do not liquefy at room temperature regardless of pressure applied?
O2 and Medical Air
What occurs to non-liquified gas contents as volume decreases?
Pressure decreases
What type of relationship is seen between pressure and volume for non-liquified compressed gases?
Linear (P1/v1=p2/v2)= Boyle’s Law
What is a liquefied compressed gas?
A gas that becomes liquid at ambient temperatures and at pressures from 25-1500 PSI
Give an example of liquefied compressed gas that we use
Nitrous oxide
What does the pressure of a liquefied compressed gas depend on?
Vapor pressure which is not an indication of remaining volume
At what level does a liquified compressed gas have to be at to see a pressure change on the gauge?
Over 95% empty
What does the food and drug administration regulate for gas cylinders?
Gas purity
What does the department of labor/OSHA regulate for gas cylinders?
Employee safety
What does the department of transportation regulate for gas cylinders?
Marking, labeling, storing maintenance, transportation and disposition
How often are gas cylinders inspected and tested?
Once every 10 years
What is required of a medical gas cylinder for MRI?
Aluminum = 3AL or 3 ALM
Where would we find the conical depression that fits the retaining screw on the yoke of gas cylinders?
On the cylinder on the back of the machine
4 points about the handle of gas cylinders
- Opens/closes cylinder
- Turns counterclockwise to open for safety
- Also called cylinder wrench
- Must have one for every machine to be readily used
What does the safety relief component of medical gas cylinders allow for?
Spring-loaded mechanism to allow venting of gas, if pressure is increased it allows gas venting and then recloses/seals after pressure is normalized inside cylinder but leaks can occur
What is the ideal gas law?
(P1V1/T1)=(P2V2/T2)
What is the most common gas cylinder size?
E
Color, liters when full and PSI of O2 cylinder
- Green
- 660L
- 1900 PSI
Color, liters when full and PSI of Air cylinder
- Yellow
- 625L
- 1900 PSI
Color, liters when full and PSI of Nitrous Oxide
- Blue
- 1590L
- 745 PSI
What was found regarding cylinders and irregularities?
Some have irregularities or faulty constructions and should be inspected by the facility as well prior to use
Which cylinder must be secured/locked up to prevent access and abuse?
Nitrous oxide
Where are cylinders not to be stored?
In the OR, they must have a designated storage area
5 points to consider when opening a gas cylinder?
- Open valve slowly and slightly prior to installation to clean out the valve port
- Check pressure
- Open away from patient
- Face valve away from people
- Correct any leaks
What piece of a cylinder if missing could potentially cause a leak?
Sealing washer
How many different pin positions are possible for gas the PISS?
7
What is PISS?
Pin Index Safety System (PISS)
Why are pipeline systems used?
Pipeline/central gas supply systems are used to deliver gas to anesthetizing locations and patient care areas because e-cylinder use is not enough
What is the pipeline pressure in the US?
380 KPA or 55 PSI
What is the most frequently reported problem in pipeline systems?
low pressure
What is required of pipeline systems?
Must have a two, 2 day supply banks, one primary and one reserve for a total of 4 days for oth
What is the reserve supply of pipeline systems used for?
Emergencies or failure of primary supply, they are in different areas with different routing
What must occur with liquid oxygen for it to be cost effective?
It must be in constant use to be cost effective or pressure increases as the liquid boils and is then vented in the atmosphere
Why is N20 supplied by a manifold cylinder system?
Because regulator prone to freezing
What do air supply sources use?
Manifold or compressors, important for intake locations are free of contaminants
What do air systems needs to do to qualify for medical use?
Need to dehumidify
What do N20 and Air supply systems have?
A series of valves, pressure regulators, and alarms just like our anesthesia machines to regulate pressure and signify problems
Where do the pipeline systems terminate?
In the OR or ICU
What is an important regulation for pipeline systems?
Name, pressure and flow direction must be clearly marked every 20 feet and in each room
Compare oxygen tank diameter to other gases
It has a different outer diameter than other gases
What do shut off valves allow for?
Certain areas in the piping system to be isolated for maintenance or problems
3 Mandatory locations for shut off valves
- Main supply into building which turns everything off
- One at each riser
- One at each branch except if branch is to anesthetizing area or critical care area
When are pipeline area alarm systems checked? tested?
Checked daily and tested monthly
When do pipeline area alarms sound?
If the pressure increases/decreases at 20% from normal line pressure
3 requirements for pipeline alarm systems
- Must be audible and visible
- Labelled for gas and area
- Personnel must know what to do if sounds
6 Conditions for pipeline alarm systems to sound
- Main supply reaches the daily average
- Main supply not at normal operating pressure
- Reserve supply has been reduced to one day supply
- Reserve supply being used
- Reserve supply decreased pressure
- Humidity of medical air unsuitable
What type of connections do gases have into the wall?
Connection into wall uses quick connectors that have a pair of male and female parts that only connect when the proper alignment is achieved. Each gas has a specific shape and spacing but are ore prone to leaks Vs DISS system
What type of connection do gases use into the machine?
Station outlets uses DISS (Diameter index safety system)
What is a vaporizer?
A device that changes a liquid anesthetic agent into a vapor for inhalation
What must we add to together in a breathing system?
Controlled amount of vapor to fresh gas flow
What are vaporizers calibrated at?
Sea level and is affected by barometric pressure changes
What is our responsibility in regards to vaporizers?
To acquaint ourselves with the vaporizers at your facility
What are the 4 stages of anesthesia?
- Analgesia
- Delirium
- Surgical
- Respiratory cessation
What is the vapor pressure of a liquid?
The equilibrium pressure of the vapor above its liquid
What does the pressure of the vapor result from?
Evaporation of the liquid above the liquid in a closed system at a constant temperature
What does increasing temp do to vapor pressure?
Increasing temp increases vapor pressure, they have a linear relationship
What is the effect on vapor pressure from barometric pressure?
VP is not influenced by barometric pressure
What is vapor pressure dependent on?
liquid and temperature
When is the gas phase above the liquid is said to be saturated?
When it contains all vapor it can hold at a given temperature (Saturated vapor pressure SVP)
What is the saturated vapor concentration (SVC) calculated by
SVP/Atmospheric pressure (must be diluted by a bypass gas flow)
trade name and vapor pressure of isoflurane?
- Forane
2. VP: 238 Torr
trade name and vapor pressure of desflurane?
- Suprane
3. 664 torr
trade name and vapor pressure of sevoflurane?
- Ultane
2. 160 torr
What do we do to common volatile agents to level the playing field?
We express gas concentration in partial pressure and volumes percent (MAC)
Two forms of expression of gas concentration?
- Volumes percent
2. Partial pressure
Describe volumes percent expression of gas concentration
Concentration of a gas in a mixture expressed as a percentage of 100% at 1 atm (PP/TP * 100%)
What is MAC described in terms of
Volume percent
What does volumes percent indirectly relate to
patient uptake and anesthetics depth
Is volume percent influenced by barometric pressure?
yes
Describe partial pressure expression of gas concentration
The pressure exerted by any one gas in a gas mixture on the total gas mixture
What is partial pressure dependent on?
Temperature
What does partial pressure directly relate to?
Patient uptake and anesthetic depth
How does the potency of the partial pressure of gases change when barometric pressure increases or decreases?
No change, there is the same potency no matter what
Definition of heat vaporization
The number of calories necessary to convert 1G or 1mL of liquid into vapor
Where does heat flow from to compensate for the loss of heat in the liquid from entering the gas phase?
surrounding vaporizers
How is equilibrium established with heat vaporization?
Heat lost to vaporization = heat supplied by surrounding vaporizer
How do manufacturers account for the cooling of vaporizers?
they used certain metals
What is the definition of specific heat?
The quantity of heat required to raise the temperature of 1 gram of a substance 1 degree celsius
What does it mean if something has a higher specific heat?
temperature changes more gradually
What is the standard for specific heat?
H20 is the standard, 2 cal per gram per 1 degree
What must specific heat be considered for?
Maintaining a constant temperature to the vaporizer
What is the definition of thermal conductivity?
The speed of which heat flows through a substance
What does higher thermal conductivity mean
Better conductor of heat
What must be considered in choosing a material/metals for vaporizer construction?
Specific heat and thermal conductivity
What do we want in regards to specific heat and vaporizers?
Want a higher specific heat because it is harder for the temperature to change, which means the vaporizer is less likely to change with gas leaving
What are the two kinds of vaporizer design?
bypass vaporizers and electronic vaporizers
How much is FGF through a pipeline system?
35-75L/min
Why are vaporizers placed where they are?
So that liquid can become vapor and then saturate the body
Calculation of vaporizer output?
At a steady state, the total volume of gas leaving the vaporizer is greater than the total volume that entered due to the additional volume attributed to anesthetic vapor at its SVC (saturated vapor concentration)
Compare vapor pressure of an anesthetic gas at room temp to the partial pressure necessary to achieve anesthesia
It is more, that is why the vaporizer dilutes the anesthetic to a useful concentration (it is more potent)
What is the splitting ratio?
Some gas flows into vaporizer chamber, some gas flows into bypass
What does the splitting ratio depend on?
The anesthetic agent/concentration, size of the adjustable orifice, total gas flow, and heat of vaporization
Does the temperature compensating mechanism for vaporizers produce instantaneous results?
No, the anticipated concentration may not be accurate until compensation occurs
Describe bypass vaporizers
No volatile is attached to flow through bypass chamber vs vaporizing chamber
With bypass vaporizers, what does the splitting ratio equal?
vaporizing/bypass
What does increasing the splitting ratio mean with bypass vaporizers?
More fresh gas goes into vaporizing chamber and therefore more goes to the patient
What happens to the splitting ratio if you cool the bypass vaporizer?
it gets smaller, so less goes to to the patient, you need to increase MAC and increase FGF
Describe electronic vaporizers
Computer drive, calculates either volume of carrier gas to produce the desired concentration or the amount of liquid agent needed to be injected into carrier flow
What is the desired concentration based on from electronic vaporizers?
What you have dialed into the dial or machine
Describe injection of vaporizers
Inject known volume liquid anesthetic into known volume of gas
Describe flow-over of vaporizers
Carrier gas passes over surface area of a liquid; increasing surface area increases the efficiency of vaporization
How do we fix the energy lost in vaporization?
Thermocompensation
What does heat of vaporization (HOV) do to the vaporizer?
Decreases the temp and decreases output of gas/vapor and splitting ratio will decrease without thermocompensation, meaning no steady concentration is given to the patient
What is an example of a gas that we use supplied heat to maintain heat?
Desflurane
Where might intermittent back pressure (IBP) come from?
O2 + OR + Pressure from inspiration during ventilator use
What can IBP cause?
A pumping effect or pressurizing effect on vaporizer outputs
What does IBP most commonly have to do with?
Ventilator and flush valve use
What is the end result of the pumping effect from IBP?
Increase of vapor output, causing more to get to the patient
What is the pumping effect due to?
Back pressure during inhalation at low FGF causing increased flow into the vaporizing chamber so more than usual vapor is picked up
When is the pumping effect more commonly seen?
Low FGF, large pressure fluctuations, and low vaporizer settings
What helps minimize the pumping effect?
Presence of the pressurizing valve, unidirectional valve, and pressure relief valve
What is the end result of the pressurizing effect?
decrease in vapor output causing decreased delivery to the patient
What is the pressurizing effect due to?
Back pressure at high FGF causes increased density into vaporizing chambers so less than usual vapor picked up
When is the pressurizing effect more commonly seen?
High gas flows, large pressure fluctuations, and low vaporizer settings
What does FGF directly affect?
Vaporizer output
How many L/min is considered high fresh gas flow?
10L/min
When is there a higher chance of gas being rebreathed by the patient, in high fresh gas flow or low fresh gas flow?
Low fresh gas flow
With what type of fresh gas flow does inspired concentration = vaporizer setting?
high fresh gas flow
With what type of fresh gas flow do we need agent analyzer to get the true value of gas getting to the patient?
low fresh gas flow
Describe high FGF
Gas delivery is higher than patient minute volume, there is no recycling and the patient is getting closer to exact gas concentration and are getting what is on the dial
When is low FGF used?
maintenance phase of anesthesia
How many L/min would be considered low fresh gas flow?
2L/min
What is low fresh gas flow the difference between?
Vaporizer setting and inspired concentration
Which type of fresh gas flow does it take longer for the patient to reach equilibrium?
low fresh gas flow
6 standard regulations for vaporizers
- Average concentration +/- 20% setting
- Gas may not pass through more than 1 vaporizer (safety)
- Output of vaporizer <0.05% in off
- All control knobs turn counterclockwise
- Filling levels displayed
- Can not overfill when in normal operating position
What is the most common type of vaporizer mounting system?
Detachable
When might it be a huge benefit for easy removal of vaporizing mounting systems?
malignant hyperthermia
What does the interlock device for vaporizers prevent?
More than 1 vaporizer being turned on at a time
3 vaporizer hazards?
- Incorrect agent
- Tipping
- Overfilling
2 steps that must be taken if contaminated filling occurs of vaporizers
- Must be completely drained and all liquid discarded
2. FGF run until no vapor detected
Describe tipping of vaporizers
Liquid may get into bypass our outlet causing an increased concentration of agent
What mode should vaporizers be placed in prior to moving to prevent tipping?
Off/travel mode
What do you do if a vaporizer is tipped?
High FGF run with low concentration of vapor until excessive vapor exhausted
3 descriptors of overfilling vaporizers
- Liquid may enter fresh gas line or cause vaporizer failure
- Potential for lethal dose
- Can occur during tipping or filling with the on setting
2 reasons why leaking of vaporizers happens
- Failure to tighten filler cap
2. Fill valve not closed - malfunctioning mount/vaporizer pollutes or can probably smells
What is the most common cause of no vapor output?
vaporizer is empty
3 reasons for no vapor output
- empty
- incorrect mounting
- overfilled = no output because of vaporizer failure
What are anesthesia gas delivery systems composed of?
Anesthesia machine, vaporizers, ventilator, breathing circuit, and scavenging system
Describe the gas delivery from start to end (6)
- Gas source delivers gas to machine
- Gas delivered to flowmeters and vaporizers
- Gas mixture goes to common gas outlet (CGO)
- Gas flows to breathing circuit to the pat
- Gas leaves pt through breathing circuit
- Excess gas either via the APL valve/scavenger or ventilator
Who are the two large manufacturers of anesthesia gas delivery systems in the united states
Draeger Medical and GE
What do older anesthesia machines lack that newer machines do have?
Safety features
What did older anesthesia systems require to work?
Supply of gas under pressure and were pneumatic, they had no electrical functions
What electrical components of an anesthesia machine are active if the master switch is off?
Battery charger and electrical outlets for additional monitors
What pneumatic functions are maintained when the anesthesia machine is off?
Oxygen flush valve and axillary oxygen flowmeter
What occurs when the master switch of an anesthesia machine is on?
the electronics go through a powering up protocol that usually includes an automated machine checkout
When can the anesthesia machine checkout be overridden?
In an emergency
What permits the delivery of gas from the flowmeters and vaporizers?
The pneumatic functions on anesthesia machines
What do the red outlets connect to?
Back up generator
What do all contemporary anesthesia machines incorporate?
Electrical systems and require a connection to electrical power
What occurs if requirements exceed the anesthesia machine outlet?
circuit breaker will activate
When should anesthesia machine checkouts occur?
Take place before the first case of the day and if any changes are made to the system
What does the abbreviated check of the delivery stems between cases include?
High pressure check to check for pressure problems in the low pressure system
What is one of the most important steps often overlooked in the anesthesia precheck?
Machine and airway, the immediate presence of ventilation modalities in the event of a power outage or failure oxygen cylinder supply and ambu bag
What is Ohm’s Law?
Flow = Pressure/Resistance
What is the basic function of any anesthesia machine?
To receive compressed gases from their source and create a gas mixture and flow rate at the CGO to deliver to the patient
What is required of yokes for oxygen and nitrous tanks?
There must be one for each
What does the hanger yoke assembly prevent?
Prevents gas from being transferred from a cylinder with higher pressure to one with lower pressure if both are in a yoke and ON thus prevents the unnecessary depletion of gas
What is the gauge pressure?
measured pressure of a gas above ambient atmospheric pressure
3 descriptors of bourdon tubes (curved hollow tubes) of cylinder pressure indicator/gauges
- Increase pressure straightens curve
- Falling pressure causes curve to redevelop
- Motion is transmitted to gauge
What is a pressure regulator?
Device that converts a high, variable input gas pressure to a constant, lower output presssure
Why are pressure regulators also called reducing valves?
Reduces high, variable pressure in cylinders to lower constant pressure for machine
Which gases are regulators required for?
Each gas supplied by a cylinder
Why do reducing valves help to prevent?
They make it so we do not have to constantly adjust flowmeter to provide constant flow
What gas specific connections are used for entry point of gases from pipelines?
DISS (Diameter index safety system)
Which pipeline inlet connections are required?
Oxygen and nitrous
What must pipeline inlet connections contain?
Unidirectional check valves to prevent gas returning or flowing back into the pipeline
When will the indicator of pipeline pressure be most accurate?
When the cylinder is 0
Describe a high pressure system
Includes parts of upstream of the cylinder pressure regulator aka first stage regulator
What is the first stage regulator?
Converts high pressures to constant lower pressure of 45psi, which is oxygen cylinder pressure regulator
High pressure gas systems have oxygen pressure between what psi’s?
45-2200 psi
Describe intermediate pressure systems
includes parts between cylinder pressure regulator and pipeline gas inlet to gas flow control valves, with oxygen pressures between 16 and 55 psi, can flow and pressurize gas in multiple directions
How does gas enter the machine from the first stage regulator or cylinder pressure regulator?
through intermediate pressure system
What is the intermediate pressure system pressure if the master switch is off?
0
Why is there a deliberate difference in supply pressures between the pipeline (50-55psi) and cylinder oxygen (40-45psi)
Because if the cylinders are open, the machine will preferentially receive oxygen from the pipeline due to this pressure difference
If pipeline pressure drops below the cylinders what occurs?
The pipeline will preferentially receive oxygen from the cylinder
What should be done to the gas cylinder to prevent exhaustion and leakage of gases from cylinders?
It should be turned off
Describe low pressure systems
includes all parts downstream of the gas flow control valves, so extends from flowmeters to CGO with pressures normally slightly greater than atmospheric pressure
Describe pressure in low pressure systems
Pressure is variable and depends on flow from flowmeters and back pressure from breathing circuit
5 parts that low pressure systems include
- Flowmeters
- Hypoxia prevention devices
- Unidirectional valves
- Pressure relief valves
- Common gas outlet (CGO)
What should machine piping leak no exceed?
25mL/min inside machine
Describe the common gas outlet (CGO)
Receives all as from machine and delivers mixture to breathing system to deliver to the patient
What should the common gas outlet not be used for?
supplemental oxygen
What is the unidirectional valve located at the pipeline inlet used for?
to prevent pipeline back flow
Where is the outlet check valve?
Upstream from oxygen flush valve
What does the outlet check valve being upstream from oxygen flush valve prevent/lessen?
Back pressure from oxygen flush or breathing circuit so it prevents reverse gas flow (reduces IBP)
What does the pressure relief valve prevent?
The buildup of pressure upstream of the outlet check valve
Where is the pressure relief valve?
Near the CGO and open to atmosphere to vent gas if preset pressure is exceeded
what does the pressure relief valve limit?
Limits the ability of machine to provide adequate pressure for jet ventilation
What regulates flow of oxygen, medical air and other gases in the anesthesia machine?
flow adjustment controls
How many flow adjustment controls are there?
Only one for each gas
Where must the flow adjustment controls be located?
Adjacent to its flowmeter and turn in only one direction
Describe oxygen flow knobs
Must be fluted and larger than other gases
What do flowmeters indicate?
Rate that gas is passing through piping into CGO then to patient
How is oxygen supply pressure to the flowmeters regulated
A constant, power pressure by a second stage regulator
What type of tube is used for flowmeters?
Thorpe tube
What must flowmeters be marked with?
Appropriate color and chemical symbol of gas
Where does the flowmeter sequence all gas flow from?
bottom to top and left to right
Standards of oxygen flowmeter?
Oxygen flowmeter to be placed on Right side, closest to CGO, that way if a leak occurs with other gases, it is unlikely to result in a hypoxic mixture
Where does the oxygen flush valve receive oxygen from?
Pipeline inlet or cylinder pressure regulator
Where does the oxygen flush valve send high flow O2?
To the CGO and the pressure could increase the supply pressure at the CGO, without the presence of pressure relief valves to appropriately regulate it
5 Requirements of oxygen flush valves?
- Operable with 1 hand
- Single purpose
- Self-closing
- Designed to minimize accidental use
- Have flow between 35-75 L/min
3 hazards of oxygen flush valves
- Potential for sticking of valve
- Barotrauma
- Anesthetic awareness
What does turning the master switch on for the oxygen failure protection device cause?
Causes oxygen to pressurize and holds open a pressure sensor shut-off valve
Describe the Oxygen Pressure Failure aka Oxygen Failure Protection Device (OFPD)
Shuts off or proportionally decreases nitrous to maintain a minimum 19% O2 flow at CGO using oxygen failure safety switch
When does the oxygen failure alarm sound?
When pressure falls below threshold, approx 30 psi, an alarm sounds within 5 seconds
What type of machines are hypoxia prevention devices required on?
Contemporary machines
2 factors of mandatory minimum oxygen flows
- Minimum of 50-250ml/min flow
2. Activated when master switch is on
What does the minimum oxygen ratio use/
Mechanical linkage with nitrous to limit nitrous flow when it is given in tandem with oxygen
When does the mechanical link engage with hypoxia prevention devices?
When oxygen concentration less than 25% to maintain a minimum oxygen concentration delivered and prevent a hypoxic gas mixture
Describe axillary oxygen flowmeters
Delivers oxygen in case of electronic power or system pressure failure, connect ambu bag or modified anesthesia circuit in order to ventilate the patient
What flow of O2 does the axillary oxygen flowmeter allow?
10L/min
When is the axillary oxygen flowmeter active?
when the master switch is off
When should the batter backup of anesthesia machines be at the highest level?
when they are plugged in
What does duration of the anesthesia machine backup depend on?
Power usage, manual ventilation uses much less power than ventilator usage
6 sources of anesthetic gas contamination
- APL valve
- High and intermediate pressure systems
- Low pressure systems
- Ventilator
- Anesthetic errors
- Cryosurgery
What is the outlet for anesthetic gases during spontaneous and assisted ventilation?
APL valve
How much FGF can exit through the APL valve?
5L/min
Describe the APL valve
Spring-loaded and only requires minimal positive pressure to open and allow the exit of waste gas from the circuit
What does the high and intermediate pressure systems include?
The N2O pipeline and cylinder supply as well as the machine piping that feed the N2O flowmeters
What can leaks in the high and intermediate pressure systems cause?
Increase in waste gas in the OR, common site of leaks are connections
Describe the components of low pressure systems (8)
- N2O flowmeter
- Vaporizers
- Fresh gas lines from the machine to the breathing circuit
- CO2 absorber
- Breathing hoses
- Unidirectional valves
- Ventilator
- Components of scavenger system
3 reasons for leaks at the CO2 absorber of low pressure systems
- Loose seals/connections at valves and circuit
- Vaporizer mount
- Scavenger system
What can high pressure in low pressure systems cause?
Leaks in a direct fashion and even with a functioning scavenger system can have a 2L/min leak
What occurs if ventilators have an internal leak?
mixing of gases
What is 94-99% of waste gas due to?
Anesthesia technique error
7 Anesthesia Technique errors
- Insufflation errors
- N2O on with open circuit
- Poor airway seal
- Uncuffed tracheal tubes
- Post procedure circuit d/c
- Overfill and gas spillage around vaporizers
- Letting active gases exit an open circuit
What is waste from cryosurgery due to?
The use of liquid N2O as a tool intraoperative, the gas evaporates in the OR
What is a Nonrecirculating ventilation system?
Used in most ORs; pumps in air from outside and removes stale air with a variable amount of air exchanges per hour, air flow patter and workstation location matter as well as generation of airflow
What is a Recirculating ventilation system?
More economical; partially recirculates stale air; each air exchange has part fresh outside air and part filtered and conditioned stale air
Where are recirculating ventilation systems popular?
Locations with temperature extremes
What type of flow is optimal in nonrecirculating ventilator systems and why?
Laminar flow is optimal to prevent air mixing and reduce hot spots
What are hot spots in the OR?
Heavily contaminated air pockets by waste gases
What is the recommended air exchange per our for OR ventilation systems?
15-21 per hour
What, if functioning properly on anesthesia workstations, can reduce trace concentrations of gases by 90%?
Scavengers systems
4 parts of the Scavenging system of anesthesia workstations
- Relief valve (APL and vent pressure relief)
- Tubing to the scavenging interface
- Interface
- Disposal line
Describe Ventilator pressure relief valve (VPR)
This is how waste gases leave ventilator, during inspiration the valve is closed due to positive pressure transmitted from the ventilator
What does a closed scavenging interface include?
A bag for waste gas that is then sent to vacuum or ventilation system
With a closed scavenging system what occurs if the vacuum system fails?
There is excess pressure in the reservoir bag that causes the APL to open and vent waste gases into the room, will have visual over distention
Describe open scavenging interface
Valvless and uses continually open relief port to avoid positive or negative waste gas buildup
What do open scavenging interfaces have to show the waste gas being evacuated?
Flowmeters, may incorporate a reservoir bag
What does it mean when we say that we have an active gas disposal route?
Using a vacuum or evacuation system
What does it mean when we say that we have a passive gas disposal route?
The OR ventilation system or through the wall disposal
What is the benefit of low flow scavenging systems?
lowers cost and carbon footprint
What should the vacuum/suction for active gas disposal be able to vent in liters per minute?
30L/min of air
What does scavenging of the breathing circuit increase?
The hazards of anesthesia administration
Where can excessive positive or negative pressure in the scavenger system due to malfunction be directed?
Into the breathing circuit
What are two gases that are ventilator driven?
Oxygen and medical air
What can ventilator drive gas increase if part of the waste gases?
Fire risk due to higher concentrations of oxygen
How does scavenging systems vent gases?
Relief valves
Is there a safe level of trace gases?
None has been established and there are no formal OR monitoring systems
What type of fresh gas flow minimizes negative effects and costs
Low FGF
Are Or and ICU ventilators the same?
No
What must ventilator management augment or complement?
The entire anesthetic picture for ventilation and oxygenation
What can increasing inspired Oxygen concentration and airway pressure increase?
Oxygenation
What dictates minute ventilation?
Quantity of CO2 produced
What is minute volume made of?
Alveolar and total dead space ventilation
What is dead space ventilation normally when compared to minute volume?
1/3 of minute volume
What is dead space?
The portion of tidal volume that does not take part in gas exchange
What can total dead space increase to under general anesthesia and IPPV?
45% of tidal volume, so minute volume will increase
What is the total work of breathing?
Sum of the work related to overcoming lung and chest wall elasticity and the work related to overcoming the resistance of the circuit, ETT, and large and small airways
What is the purpose of the ventilator?
To perform work of breathing
What is the force exerted by the ventilator measured as?
Pressure
What must the pressure provided by a ventilator overcome?
Compliance and resistance during inspiration
What type of process is exhalation with mechanical ventilation?
Passive with mechanical ventilation
What type of process is inhalation with mechanical ventilation?
active process
What can compliance and resistance be seen as and what does it result in?
The load against the inspiratory pressure and results in tidal volume and inspiratory flow
What is inspiratory flow?
The amount of flow used to make the breath
What do changes in inspiratory pressure yield changes in?
Both tidal volume and inspiratory flow
What can changes in desired inspiratory flow be accomplished by?
Making changes to inspiratory pressure, Vt or both
What can changes in desired Vt be accomplished by?
Changes in inspiratory pressure and or flow
What varies when inspiratory flow is matched with a desired Vt?
inspiratory pressure varies with the given load
What varies when inspiratory flow is matched with a desired inspiratory pressure?
Tidal volume with the given load
What are the 3 interdependent respiratory variables?
Minute volume, Vt and respiratory rate
Why is the I:E ratio important?
it affects ventilation and oxygenation
What factors of the ETT can affect resistance to breathing
- Length of tubing
2. Diameter of tubing
5 adverse factors of ETT
- Increased secretions due to cough suppression
- Depression or damage to mucociliary function
- Increased water loss due to decreased humidification
- Thicker secretions from dry gases
- Heat loss
What type of pressure does tracheal suctioning create and what does it cause?
Negative airway pressure which can decrease inspired oxygen and promote atelectasis
What can occur with the increase in intrathoracic pressure cause by IPPV
Reduction in venous return and cardiac output
What is the effect of PEEP on the cardiovascular system
Reduction in venous return and CO due to increased intrathoracic pressure
What is the biggest benefit from tracheal intubation?
Protection of the airway from secretions and mechanical ventilation can reduce the work of breathing and allow muscle recovery
What does mechanical ventilation afford?
Consistent ventilation and deliver gases intraop and also allows the aneshetists to make changes based on patient response to surgical conditions
What risk does IPPV present? (2)
barotrauma and alveolar damage
What can make IPPV challenging due to inconsistent compliance?
Disease states that affect lung uniformity such as COPD, pulmonary fibrosis, and pulmonary scaring
What is optimal PEEP?
5-15 cmH20
Recommended Vt?
6-8 mL/kg
What can the drive mechanism that describes how ventilator pushes gas to the patient be classified as?
Bellows or piston
What is the classification of ascending/descending bellows based on?
Bellow movement on exhalation
Benefit of piston ventilators?
Have great Vt accuracy, but leaks can also occur with this drive mechanism
What does the cycling behavior of mechanical ventilation describe?
The transition of inspiration to expiration and the reverse
2 factors that can control ventilator cycle
volume or pressure
What do most ventilators cycle exhalation to inspiration based on?
time
3 categories of ventilator modes
- Controlled breathing modes
- Assisted or supported modes
- Spontaneous breathing without assistance or support
Describe patient contribution in controlled breathing modes
Patient cannot contribute any effort to the work of breathing
What is the fixed parameter with VCV?
Volume
What must we set with VCV?
Vt, RR, and I:E ratio (Will get the same each breath)
How is PAP related to airway resistance and compliance with VCV?
directly related to resistance and inversely related to compliance
What can increase the risk of barotrauma with VCV?
worsening resistance (secretions, bronchospasm) and compliance (fluid overload, abd distention)
Describe PCV
Pressure is the fixed parameter
What is controlled with PCV? What must we set?
Pressure is controlled, we must set PAP, RR, and I:E ratio
With VCV and PCV, inspiratory time is calculated by the RR and I:E ratio, what is different with PCV?
Flow is varied to match desired PAP
Describe VG-PCV
allows ventilator to change inspiratory pressure based on the compliance of the lungs (we set PEEP)
What does a sudden improvement in compliance result in with VG-PCV?
Larger Vt and hyperventilation (insufflation is lost in laparoscopic procedures)
What does VG-PCV allow the ventilator to do?
To adjust inspiratory pressure over several breaths to maintain consistency Vt and ventilatory parameters
What contributes to the work of breathing with assisted and supportive ventilator modes?
The patient and the ventilator
What were assisted and supportive ventilator modes created as a solution for?
Pulmonary recovery in critically ill patients who require prolonged ventilation
What do assisted and supportive ventilator modes allow for the augmentation of in the OR?
Patient’s breathing effort while under general anesthesia
What do assisted and supportive ventilator modes decrease the risk of? (3)
hypoxemia, hypercarbia, and dissynchrony that would occur in controlled modes
Describe ACV
Patient’s effort to breathe causes a decreased pressure and when a predertime negative pressure is reached the ventilator is triggered to deliver a preset Vt
Where do we see ACV used the most?
ICU’s not in the OR
What occurs if the patients work of breathing triggers the ventilator to deliver breaths over the set RR with ACV settings?
Controlled breaths outside the WOB will not be delivered
With ACV, what happen if there is apnea or a pause?
The controlled ventilation mode will deliver breaths at the preset parameters
What is the minute ventilation the sum of with ACV?
Both the delivered and patient triggered breaths
Where does the difference between assist and control ventilator settings?
The change caused in airway pressure and that determines ventilator response
What is the pressure equivalent setting of assisted ventilation?
PSV
What is PSV used in the OR for?
To support patient breathing during GETA with ETT or LMA, often used with CPAP mode
What does PSV give patient control of?
Their respiratory effort or spontaneous breaths on the ventilator and optimizing their breathing
What must we set with PSV?
Inspiratory time, PAP, and the trigger for pressure or flow
2 types of surgeries we could use PSV for
- Lung cases
2. Thoracic cases
What should low pressure PSV ideally overcome?
The resistance of the ETT
Describe IMV
Anesthetists sets mandatory breaths by either pressure or volume at a defined RR and inspiratory time
What causes stacking of breaths with IMV?
Patient breathing at the same time the vent is delivering the breath, increases the risk of barotrauma
Describe what we set with SIMV
Mandatory volume or pressure, RR and inspiratory time
Describe SIMV
Gives a breath at the beginning or end of an interval by monitoring patient effort and if the patient effort is not causing changes in set pressure or flow, then mandatory breath is given
What does SIMV appear to be the same as when there is no patient effort?
VCV or PCV
What does allowing spontaneous ventilation without assistance or support allow for?
Monitoring of ventilatory parameters of the patient’s work of breathing
In a steady state, what two conditions can occur to change respiratory parameters when we aren’t giving support or assistance?
- Airway pressure can start and end at atmospheric pressure (flow-by)
- Addition of positive pressure to the airway or continuous positive airway pressure
What is CPAP set by on the anesthesia workstation?
Ventilator setting or by APL valve
What does the CPAP number equal?
The airway pressure between exhalation and inhalation, when gas flow within the airway is zero
How can we approximate CPAP number if the ventilator does not have a CPAP mode?
Evaluating peak expiratory pressure
What does CPAP during anesthesia encourage?
Alveolar recruitment and improved oxygenation, but can cause a rise in intrathoracic pressure
What can be the effect of CPAP on patient’s with obstructive lung disease?
Increased air trapping and impaired ventilation and oxygenation
Define high frequency ventilation (HFV)
60-3000 breath cycles/min or rate exceeding 150 breath cycles/min
Describe high frequency positive pressure ventilation (HFPPV)
uses nasotracheal tube or catheter without side holes to insufflate an anesthetic gas mixture; small Vt and high RR
Describe high frequency jet ventilation (HFJV)
HFV to deliver jet of gas through a catheter in the ETT; high pressure of jet gas flows into the airway with small Vt and these breaths decrease distal airway and alveolar pressures
When can HFPPV be used?
can be use in airway and thoracic procedures
When can HFJV be used?
ventilation and oxygenation of difficult airways and in lung and laryngeal surgeries
Describe high frequency oscillatory ventilation (HFO)
uses high frequency, small Vt, 200-2400 breaths/cycles/min and the exhalation phase is not passive with oscillatory intervals, increased dead space ventilation
When can HFO be used?
Lung surgeries to decrease lung pressure and peripheral inflation and can prevent barotrauma in neonates
Describe Airway pressure release ventilation (APRV)
not been found to be useful in OR; similar to BiPAP, during inspiration high pressure CPAP is delivered to patient but ventilation depends on the patient’s ability to generate adequate Vt and during exhalation, lower airway pressures can produce PEEP
What can cause over pressurization of the airway with use of ventilators
- Patient coughs
- Excessive inspiratory ventilator settings
- Oxygen flush valve use during inspiration
Other complications of ventilator use? (7)
- Drying of secretions
- Decrease temperature
- Hyper/hypocarbia
- Hypoxemia due to incorrect ventilator settings
- Hypotension
- Barotrauma
- Flow obstruction
What should you do if ventilator malfunction occurs?
Disconnect the patient from the circuit and backup ventilation should be employed, you may have to get a new machine/workstation during the case
What is the definition of breathing systems
a pathway connected to the patient through which gas flow occurs at respirator pressures into which gas mixture is dispensed from fresh gas inlet to gas scavenging
What is the mission of breathing machines? (5)
- Receives gas mixture from the machine
- Delivers gas to the patient
- Removes CO2
- Allows spontaneous, assisted or controlled respiration
- Provides gas sampling, measures airway pressure, monitors volume
When gas passes through a tube, where is the pressure lowest?
The pressure at the outlet will be lower than at the inlet
What is the drop in pressure as gas passes through a tube equal to?
The resistance which was overcome
What does resistance to gas flow vary with?
Volume of gas passing through the tube
Describe laminar flow (3)
- Flow is smooth and orderly
- Particles move parallel to the tube walls
- Flow is fastest in the center where friction is the least
What is the formula for change of pressure?
Change in pressure = (L * v * V)/r^4
L = length v = viscosity of gas V = flow rate
Describe turbulent flow (4)
- Flow lines are not parallel, they are “eddies”
- Flow rate is same across diameter of tube
- Generalized when flow exceeds critical rate
- Localized when encounters constrictions, curves, valves
What are “eddies”
particles moving across or opposite
What is an increase in resistance directly related to?
Increased work of breathing
What causes more resistance, the ETT or breathing system?
ETT
What is compliance
Ratio of change in volume to change in pressure
What does compliance measure?
Distensibility (mL/cmH2O)
What is the most distensible in the anesthesia workstation?
- Breathing circuit
2. Reservoir bag
What does compliance help determine?
Vt
Define rebreathing
To inhale previously inspired gases from which CO2 may or may not have been removed
3 things that rebreathing is influence by
- Fresh gas flow
- Dead space
- Breathing system design
How does the amount of rebreathing vary with FGF?
Varies inversely with FGF
What does it mean if FGF is equal to or greater than pt Vm?
No rebreathing occurs as long as exhaled gas is vented
What does it mean if FGF is < pt Vm?
Rebreathing occurs to meet required Vm
Define mechanical dead space
Rebreathed gases in breathing system which don’t change in composition
What is mechanical dead space decreased by?
By having inspiratory and expiratory limb separation
What is apparatus dead space
Mechanical dead space
Define anatomical dead space
Patients conducting airway to alveoli; adds H20 vapor
What is anatomical dead space reduced by?
ETT (increases mechanical dead space) or tracheotomy
What causes increased anatomical dead space?
Circuits, masks, humidifiers
Describe alveolar dead space
Volume of alveoli ventilated but not perfused
Effects of rebreathing (2)
- Heat and moisture retention
2. Altered gas tensions of oxygen, inhaled agents, and CO2
6 desirable characteristics of a breathing system
- low resistance to gas flow
- minimal rebreathing
- removal of CO2 at rate of production
- rapid changes in delivered gas when required
- warmed humidification of inspired gas
- safe disposal of wastes
Describe an open breathing system
no reservoir and no rebreathing
Describe semi-open breathing systems
a reservoir but no rebreathing
Describe semi-closed breathing systems
a reservoir and partial rebreathing
Describe closed breathing systems
a reservoir and complete rebreathing but depends on FGF
What could an increase in volume delivered to a patient result from?
FGF greater than tidal volume of patient or leaks in system (modern ventilators are designed to eliminate this)
What could a decrease in volume be a result from?
- Leaks in circuit
2. Gas compression and distention of circuit
Describe dilution of gas concentration
FGF less than Vt and leaks in system
Describe uptake of gas by breathing system components (2)
- May adhere to plastics, rubber, absorbent
2. Related to time, surface area
When could gas be forced out of the system?
During positive pressure ventilation
3 requirements of anesthesia masks
- Must be clear for visualization of vomit
- Inflatable or inflated cuff to prevent nerve injury or direct pressure trauma
- Pneumatic cushion that seals to face
Where does the anesthesia mask fit?
Between the inter pupillary line and in the groove between the mental process and the alveolar ridge
What size female connection is between the Y-piece and the anesthesia mask?
22 mm
3 benefits of connectors/adapters on anesthesia workstations
- Extend distance between patient and breathing system
- Change angle of connection
- Allow more flexibility/less kinking
3 potential negatives to connectors/adapters on anesthesia workstations
- Increased resistance
- Increased dead space (pedi patients)
- Increased locations for disconnects
What is the shape of reservoir bags and why?
Ellipsoidal for 1 hand ventilation
What is the traditional volume of reservoir bags for adults?
3 liters
What is the normal range of volume in reservoir bags?
0.5-6L
What type of connector is required on the neck of reservoir bags?
22 mm female
What is the pressure in reservoir bags if it is 4x its size?
35-60 cmH2O
4 functions of reservoir bags
- Allows gas accumulation; reservoir for next breath
- A means of assisted ventilation
- Visual/tactile monitor of breathing (inflate/deflate)
- Distensibility protects from excessive airway pressure b/c pressure is generated by compliance of the bag
3 factors of breathing tubes
- Large bore, corrugated, plastic, expandable
- 1 meter in length (400-500mL/m)
- Low resistance, somewhat distensible
What type of airflow occurs through breathing tubes?
Turbulent due to corrugation
How many breathing tubes can be connected?
2
Where is the dead space of breathing tubes?
At the y piece to patient due to unidirectional gas flow, longer tubes don’t increase dead space
What do unidirectional valves ensure?
Gases flow toward patient in one breathing tube and away in another
What does failure to seal unidirectional valves cause?
Large amount of the circuit into mechanical dead space
4 requirements of unidirectional valves
- Arrows or directional words
- Hydrophobic so don’t stick
- Clear dome for visualization
- Placed between patient and reservoir bag to prevent rebreathing
What do unidirectional valves prevent
Backwards flow
2 functions of adjustable pressure-limiting valve (APL) valve?
- Controls pressure in breathing system
2. Releases gases to scavenging system
What occurs if you turn the APL valve clockwise?
Closes the valve and increases pressure
What occurs if you turn the APL valve counterclockwise?
Opens the valve and decreases pressure
3 requirements of APL valves
- Clockwise motion increases pressure
- Opposite motion decreases pressure
- An arrow must indicate direction to close valve
APL valve use during inhalation/expiration during spontaneous respiration
- Inspiration: Open or partial closed during CPAP
2. Expiration: Open
APL valve use during inhalation/expiration during assisted ventilation
- Inspiration: Partially open, excess diverted
2. Expiration: Partially open
APL valve use during inhalation/expiration during mechanical ventilation
Bypassed during inspiration and expiration
5 components of a mapleson system
- Reservoir bag
- Corrugated tubing
- APL valve
- Fresh gas inlet
- Patient connection
3 things missing in mapleson systems
- CO2 absorber
- Unidirectional valves
- Separate inspiratory and expiratory limbs
Where does the FGF enter and where is the APL valve located for Mapelson A (Magill’s System)?
FGF enters opposite of pt end and APL at pt end
What would a Mapleson A be most efficient for?
Spontaneous, unassisted pts, want lower FGF
Where is the APL valve and FGF for Mapleson B?
At a T piece, but APL is still between the FGF and the patient
With a Mapleson B, what should FGF be compared to Vm?
Should be double
Describe a Mapleson C
Identical to Mapleson B expect corrugated tubing is omitted, length of tubing is decreased
What is a Mapleson C used for?
Emergency resuscitation
Describe Mapleson D (3)
- 3 way T-piece: pt connection, fresh gas, corrugated tubing
- PEEP valves may be added
- FGF 1.5-3x Vm
When could we use Mapleson D?
Most efficient for assisted, controlled ventilation
What is the Bain modification of Mapleson D?
FGF is coaxial (runs inside of the tubing)
Describe Mapleson E
- Corrugated tubing attached to the T-piece forms reservoir
- No reservoir bag/No APL
- Used in spontaneously breathing pts to deliver O2
- Not used in anesthesia d/t difficulty scanning gases
What is the Mapleson F
Jackson-Rees modification of Mapleson E, reservoir bag is added
What is less likely to develop with Mapleson F due to no APL valve being present
Excessive pressure could build up
5 advantages of Mapleson systems
- Simple, inexpensive, lightweight
- Variations in Vm affect ETCO2 less than a circle system
- Inspiratory gas can be heated in coaxial system
- Resistance usually low
- No toxic products d/t lack of CO2 absorbent
5 disadvantages of Mapleson systems
- Require high FGF, higher cost/pollution
- Heat and humidity low in inspired gas
- Scavenging awkward
- A-C have APL close to patient
- Not suitable for patients with MH because may not be possible to increase FGF enough
What do circle systems allow for?
Circular, unidirectional flow
5 advantages to circle systems
- Relatively stable inspired gas concentration
- Conservation of moisture/heat
- Elimination of carbon dioxide
- Economy of gases
- Prevention of OR pollution
What is a big disadvantage of circle systems?
Complex design with 10 or more connections
What does the housing of absorbent canisters incorporate?
Incorporates valves that close if absorbent is removed
What does the center tube of absorbent canisters do?
conducts gas through absorbent and returns them to pt
Describe High-alkali absorbents (4)
- High amounts of potassium/sodium hydroxide
- When desiccated forms CO
- Form compound A with Sevo
- Does not change color if dry
What type of absorbent is soda lime?
High-alkali
Describe low-alkali absorbents (2)
- Reduced amounts of potassium/sodium hydroxide
2. May produce lesser CO and compound A
Describe alkali-free absorbents (5)
- Contains calcium hydroxide
- No CO formation
- No compound A formation
- Changes color if dry
- Poorer CO2 absorber
Describe lithium hydroxide absorbents (4)
- Reacts with CO2 to form carbonate
- Does not react with anesthetic agents
- Expensive
- Care with handling, very caustic, burns to skin, eyes lungs
Color when fresh and color when exhausted for phenolphthalein
Fresh: White
Exhausted: Pink
Color when fresh and color when exhausted for ethyl violet
Fresh: White
Exhausted: Purple
Color when fresh and color when exhausted for Clayton yellow
Fresh: Red
Exhausted: Yellow
Color when fresh and color when exhausted for Ethyl orange
Fresh: Orange
Exhausted: Yellow
Color when fresh and color when exhausted for mimosa Z
Fresh: Red
Exhausted: White
3 factors of the smaller granules of CO2 absorbents
- Greater surface area
- Decrease gas channeling
- Increase resistance and caking
4-mesh absorbent means what
4 openings per square inch
8-mesh absorbent means what
8 openings per square inch
What is used to decrease dust of absorbents?
Hardening agents
Absorbent/Anesthetic reaction: Haloalkene formation (3)
- During closed circuit anesthesia with halothane
- Produces BCDFE (2-bromo-2chloro-1, 1-difluorethane)
- Nephrotoxic in rats
Absorbent/Anesthetic reaction: Compound A formation
- 2-fluromethoxy-1, 1, 3, 3, 3-pentafluoro-1-propene
2. Possibly nephrotoxic in humans
5 instances which could cause compound A formation
- Low FGF
- Absorbents containing potassium or sodium hydroxide
- Higher servo concentration
- Longer anesthetics
- Dehydrated Absorbent
Absorbent/Anesthetic reaction: Carbon monoxide
- Dry absorbent with strong alkali
- Not detected by pulse ox or RGM
- Reaction is exothermic, note canister temp
- Highest levels seen with desflurane, sevo does not cause CO
What is indicated for anesthesia equipment when we start seeing signs of rebreathing on CO2 monitors?
Absorbent canister may need changed
What must manual resuscitation bags be?
Self-inflating
Describe the bag of manual resuscitation devices (4)
- Inflated in resting state
- Expands on exhalation
- If oxygen delivery source inadequate, difference made up by room air
- Rate at which bag re inflates determines Vm
What does the body of manual resuscitation devices do to exhaled gas?
Deflects them
Describe the non-rebreathing valve of manual resuscitation devices (3)
- Exhalation valve helps direct flow
- Gas flows out of bag into patient on inspiration
- Gas flows out of expiratory port on expiration
Describe bag inlet valves of manual resuscitation devices (4)
- One-way valve opened by negative pressure
- When bag squeezed, valve closes
- Prevents escape of air thru inlet
- At opposite end of bag from non-rebreathing valve
What does the pressure limiting device on manual resuscitation devices prevent?
Barotrauma and gas from entering stomach
ASTM standards of pressure limiting device of manual resuscitation devices
- If pressure limited at 60 cmH2O must have override
2. If override can be locked must be apparent and should have an alarm when override operating
Describe oxygen-enrichments devices near bag inlet valve (2)
- Limits increase in O2 concentration due to air drawn into bag
- There greater the Vm the lower the O2 concentration
Describe oxygen-enrichment devices that flow directly into the bag (2)
- High delivered oxygen concentrations
2. If flow is less than bag filling rate then inlet valve will admit air
4 additional devices that could be used with manual resuscitation devices
- PEEP devices
- Scavenging devices
- Carbon dioxide detector
- Pressure monitoring parts
ASTM standard of manual resuscitation devices (2)
- Deliver at least 40% at 10-15L/min of oxygen
2. Deliver at least 85% with reservoir
Define humidity
amount of water vapor in a gas
Define absolute humidity
Mass of water vapor present in gas in mg/H2O/L gas
Define humidity at saturation
maximum amount of water vapor hat a volume of gas can hold
Define relative humidity
percent saturation; amount of water vapor at a particular temp
Define water vapor pressure
Pressure exerted by water vapor in a gas mixture
Describe what occurs to gas as we breath
Gas moves to alveoli and becomes body temp and humidity changes by evaporation or condensation
4 effects of inhaling dry gas
- Damage to respiratory tract
- Body heat loss
- Absorbent desiccation rate increase because exhaling dry gas
- Tracheal tube obstruction causing increased resistance and WOB
3 way damage to respiratory tract can occur by inhaling dry gas
- Secretions thicken
- Ciliary function decreases
- Mucosa susceptible ot injury
5 sources of airway humidity
- CO2 absorbent
- Exhaled gases d/t rebreathing
- Low FGF (preserves)
- Coaxial breathing circuits
- HME (prevents loss)
What is the function of HME?
Conserves some exhaled heat and water and returns to patient, does not add humidification, may have bacterial/viral filtration
2 Indication for HME
- Increase heat and humidity during ventilation
2. Useful in transport situation
2 contraindications for HME use
- Thick secretion
2. Leaking or absent tracheal tube cuffs
Function of anesthesia machine humidifiers (2)
- Pass stream of gas over water, wicks dipped in water, through water
- May be heated or unheated
5 standard requirements of anesthesia machine humidifiers
- Volume of liquid exiting shall not exceed 20mL/hr
- If heated, gas temp not to exceed 41C and delivery tube outlet fluctuation less than 2C
- If the humidifier is tipped 20 degrees from normal, no H2O shall dump into circuit
- Direction of flow must be marked
- All calibrated controls shall be accurate +/- 5%
3 advantages of anesthesia machine humidifiers
- Place downstream of unidirectional valve
- Can deliver saturated gas at body temp or higher
- More effective than HME
4 disadvantages to anesthesia machine humidifiers
- Bulky
- Potential electrical, fire hazards
- Contamination, cleaning issues
- Higher cost than HME
What allows gas administration to the patient from the breathing system without any apparatus in the patients mouth?
Face Mask (basic skill)
When do we use face masks? (4)
- Preoxygenate/denitrogenate
- Extubation
- Entire anesthetic
- CPAP delivery in presence of resp failure (use mask straps & APL)
What do we need to adequately preoxygenate and denitrogenate? (4)
- 100% O2
- At least 3 tidal breaths
- High FGF (8-10L/min)
- No circuit leaks (mask straps help decrease leaks around mask)
What are the 4 components of the face mask?
- Body - transparent to see blood/vomit/lip color
- Seal - contacts face, inflatable
- Connector - 22mm internal diameter, circular ring with prongs for straps
- May have pacifier, ports with diaphragms, scents
Why do we perform 2-man mask ventilation?
We tried one-man mask and we didn’t get a good seal. Then tried jaw-lift and it didn’t work, we tried oral airway/nasal trumpet… THEN try two-man ventilation!
*DON’T SMOOSH THE FACE!
What are the 8 predictors for difficult mask ventilation?
- Beard
- Obese/high BMI
- Old/over 55
- Toothless/endentulous
- Snoring/short thyromental distance
- drainage tubes
- macroglossia (big FAT tongue)
- male
BOOTS + more
4 ways to overcome difficult mask ventilation?
- 2 handed technique
- Oral airway
- Turn mask upside-down
- Gel or cut the beard
*Don’t mask ventilate
11 complications of face masks?
- Allergic dermatitis
- Pressure necrosis
- Nerve injury
- Gastric inflation
- Eye injury
- Mask/wrapper defects
- Cervical spine movement
- Lack correlation between ETCO2 and arterial PaCO2
- Environmental pollution
- User fatigue
- Jaw pain
4 advantages of using mask straps with face mask?
- Lower incidence of sore throat (externally)
- Requires less anesthetic depth
- No muscle relaxants needed
- Cost-efficient
4 disadvantages of using mask straps with face mask?
- Providers hands in constant use
- More episodes of O2 desaturation
- More difficult to maintain airway
- May cause mask creep into eyes
What does the oral-pharyngeal airway (OPA) do? (3)
- Lifts tongue and epiglottis away from posterior pharyngeal wall (lifts tongue up and forward)
- Decreases work of breathing during spontaneous respiration using a face mask
- Does not cause cervical spine movement
4 Design components of OPA?
- Most made of plastic
- Bite portion must be firm enough that patient cannot close lumen by biting
- Correct size (mm)
- Color coded (size)
What should be depressed before using OPA? 2 methods of insertion?
- Pharyngeal and laryngeal reflexes
- Can go in sideways or use tongue blade…
- Avoid fingers in mouth unless you’re into biting!
- Don’t insert it upside down!
What do bite blocks do and where should they be placed?
- Prevents biting on ETT, bronchoscope, endoscope…
- Placed between teeth and gums
Another name for nasal-pharyngeal airway (NPA)? When is it tolerated?
- Nasal trumpet
- Tolerated in patients with intact airway reflexes
When are NPAs preferred? (4)
- Loose teeth
- Oral trauma
- Gingivitis
- Limited mouth opening
When are NPAs contraindicated? (3)
- Basilar skull fracture
- Nasal deformity
- Hx. epistaxis
How to prevent epistaxis with NPAs?
NPAs are NOT a great option for pt with hx of nosebleeds…
- use lubrication
- use Afrin spray to help decrease bleeding (assuming phenylephrine is not contraindicated)
What do you need to ask the patient prior to inserting NPA?
“Is one nostril easier to breathe through than the other?”
4 design components of NPA?
- Resembles shortened tracheal tube
- Flange at outer end to prevent complete passage
- Less stimulating than OPA
- Sized by diameter in mm (sizes 5-8, higher the diameter - the longer the NPA)
2 important considerations for inserting NPA?
- Correct size!
2. Lubricate!
6 complications of airways?
- Airway obstruction
- Ulceration of nose or tongue
- Dental damage
- Laryngospasm
- Retention/swallowing
- Latex allergy
What does “retention” mean in regards to airway complications?
I want them to open their mouth to retrieve oral airway, but they are still asleep and don’t let me. As they wake up more, they will spit it out.
When do we use LMAs? (2)
- Airway of choice for anesthetic we are providing - if we don’t plan to intubate
- If we have problems intubating or ventilating
What is the intermediate brdige between facemasks and endotracheal tubes?
Supraglottic airway devices - LMA
3 factors of LMA?
- Invasiveness
- Security
- Ease
Does LMA form seal over pharynx? Is it laser compatible?
- seal over pharynx: YES!
- laser-compatible: NO!
4 types of LMA?
- I-Gel
- Cobra Plus
- Aura
- SLIPA
LMA Classic: describe the shape of it
Curved tube connected to spoon shaped mask, at a 30* angle
LMA Classic: what do the two flexible vertical bars located inside the mask portion do?
Prevent epiglottis from obstructing the tube
4 additional components to the LMA classic
Inflatable cuff, latex-free, reusable, may be used in different positions
How does LMA sizing work?
-LMA sizes range from 1 to 6 (higher # is larger in size)
- Ranges differ depending on the LMA at your facility, be familiar with what your hospital uses!
- You can use size 3 on adults, primarily females.
What happens if LMA size is too small? (1)
Too small: gas leaks during positive pressure
What happens if LMA size is too large? (3)
- Won’t seat over glottis; retreats out of mouth
- Greater incidence of sore throat
- Possible pressure on lingual nerve
Technique for LMA insertion:
- Well-lubricated, cuff down (or you may like partially inflated or fully inflated)
- Held like a pencil
- Upward against the hard palate
- Follows the posterior pharyngeal wall
*We stop when we hit resistance
How do we know how much air to use to inflate the LMA cuff?
Look at the package!
*Overinflation may cause trauma or necrosis
What happens to after LMA balloon is inflated?
Neck bulges and LMA “rises” up slightly
For difficult placement of LMA, what do you do? (3)
Jaw lift, pull tongue forward, slightly inflate balloon
*Can use tongue depressor, put thumb/gauze down on tongue. May need to go in with LMA on side/upside down to get in, then flip it.
4 components of the LMA UNIQUE:
- Single-use, disposable
- Made of PVC
- Stiffer, cuff is less compliant (more rigid than the Classic)
- Insertion is the same
What makes LMA FLEXIBLE different than the others?
Wire reinforced!
in the actual tube portion
What is LMA FLEXIBLE useful for? (2)
- HEAD/NECK
(ex. tumor or turning head/neck alot) - PRONE
(Jen is not a fan of this… but UK uses LMAs in prone position)
Problems with LMA Flexible? (4)
- Tube longer and more narrow (difficult to scope thru)
- More difficult to insert
- Reinforcing wire can fracture
- No clear indication as to orientation of cuff
Why was the LMA FASTRACH DESIGNED? (2)
Designed to overcome limitations of the LMA Classic if intubating through a LMA
LMA Classic was:
- TOO FLOPPY to align perfectly with glottis
- TOO SMALL for standard ETT
Can LMA FASTRACH be used as primary airway device?
For a very short time period, YES - but it has high pressure cuff
Why do we need to lubricate the tracheal tube very well in LMA FASTRACH?
It has metal
*Usually we use glidescope over this, but this will be backup
How do we know LMA is in the correct place? (3)
ETCO2, chest rise, auscultate
Problems with LMA FASTRACH? (4)
- Unsuitable for MRI
- Intubation causes significant movement of C-spine
- Difficult insertion in pts with limited mouth opening
- Increased incidence of sore throat and dysphagia compared with the Classic
3 components of the LMA PROSEAL?
- Gastric access (more suitable to controlled ventilation)
- Wire inforced, but shorter than the Classic
- Decreases risk of gastric insufflation
*Has an extra hole at the tip, allows us to suction the stomach
1 benefit to LMA PROSEAL?
GASTRIC ACCESS PORT!
As you go up in LMA size, the cuff needs more ____?
A I R
*look at packaging
What is the point of “fixation”? What do we use?
- To keep the tube part of the LMA from moving around in the patients mouth
- Bite block or roll of gauze on each side of the mouth, sit in between the teeth
*Should be secured with tape
When is fixation contraindicated?
OPAs
What would we do if a patient had a LMA in and they started having laryngospasms? (3)
FIRST - try PPV!
If that doesn’t work, give a smaller dose of succs! (if its not contraindicated)
Larson’s Maneuver
What could cause increased cuff volume?
Nitrous
What is snoring and hooting indicative of?
Leak present, we want a good seal
How do we remove the LMA? (2)
- Deep removal
2. Awake removal
Do you deflate the cuff prior to removing LMA?
X NOPEEEE!!!! X
*If pt has a lot of secretions and the cuff is deflated, they will breathe those into the lungs!
When is deep removal of LMA appropriate?
Pt has good VT on their own, you are not assisting them, no lung issues, don’t anticipate difficulty; pt has good respiratory effort
When is awake removal of LMA appropriate?
Pt meets criteria for LMA to be removed, good respiratory effort, ask pt to open their mouth and spit it out
Does ETT or LMA provide more accurate ETCO2?
They should be close, but if there is a discrepancy it is because LMA is at greater risk for a leak
Resistance of LMA compared to ETT?
Resistance of LMA is similar to ETT, except LMA is flexible (smaller ID)
What specific situations would an LMA be useful?
- Difficult mask ventilation
- Difficult or failed intubation
- Ophthalmic surgery
- Pediatrics
- Procedures (D&C, ablation, hysteroscopy, urology, breast)
- Professional singers
Why is LMA useful in opthalmic surgery?
Lower intraocular pressure than ETT
Why is LMA useful for professional singers?
Less likely to damage vocal cords
5 complications of LMA?
- Aspiration of gastric contents
- Treatment of regurg/aspiration
- Gastric distention
- Pulmonary edema
- Trauma
How frequent does aspiration occur as a complication of LMA? Why does it happen?
2-10/10,000 adults due to inappropriate patient selection, associated with “light” anesthesia
*Often occurs without warning because airway is not secure
How do we treat regurg/aspiration? (5)
- Suction
- Control the airway
- CXR
- Antibiotics/corticosteroids
- Admitted to hospital
5 components of gastric distention associated with LMA use?
- Unlikely to occur below 20cm inflation pressure
- May use pressure control ventilation
- Risk increase if LMA not properly positioned
- Epigastric auscultation
- igel, better airway seal pressures
LMA complication - pulmonary edema?
Obstruction with negative pressure
Trauma associated with LMA use? (3)
- Epiglottis, pharyngeal wall, uvula, soft palate, tongue and tonsils
- Hematoma on vocal cords
- Esophageal perforation
What causes a sore throat to occur in 0-70% of the time with LMA? (2)
larger LMA and longer surgeries
*May benefit from lidocaine jelly as lubricant for LMA
5 advantages of LMA use?
- Ease
- Smooth awakening
- Lower OR pollution than OPA
- Avoids complications of ETT
- Frees up your hands (compared to face mask)
What makes LMA easy to place? (5)
- Little experience and training needed
- 1st time insertion, 76-96% adults
- Inserted in almost any position
- Out-of-hospital
- C-collar doesn’t interfere
How does LMA cause a smoother awakening for the patient when compared to OPA?
Fewer episodes of breath holding and desaturation
What ETT complications are avoided when LMA is used?
- Smaller increases in HR and BP
- Stress/anxiety over failure to intubate relieved
- Less trauma to lips, teeth, and gums
- No NMBD needed (MG)
- Less tracheal, laryngeal trauma/edema
- Avoids disrupting tracheal stent (used to keep trachea more open, ex. cancer pts)
Disadvantage of LMA is that it’s not suitable in every situation. Why? (2)
- Increased risk of aspiration - ex. hiatal hernia and laparoscopic surgery
- High inflation pressures - ex. poorly compliant lungs
True/False: Some resources cite losing airway skills as a disadvantage of using LMAs.
TRUE, but in Jen’s opinion that will never happen
