3/4: Inhalant Anesthesia Equipment Flashcards
What are 4 purposes for the anesthetic machine and breathing circuit?
- Deliver oxygen
- Deliver inhalant anesthetic
- Remove CO2
- Provide means for intermittent positive pressure ventilation (IPPV)
What are the 5 main components of the anesthetic machine?
FROGS:
- Flowmeter
- Regulator
- VapOrizer
- Gas supply
- Scavenger
What are the parts of the high pressure system?
- Oxygen cylinder
- High pressure hoses
- Cylinder pressure gauge
- Regulator for cylinder
What are the parts of the intermediate pressure system?
- Flowmeter
- Oxygen flush valve
What are the parts of the low pressure system?
- Vaporizer
- Breathing system
- Common gas outlet
- Common gas inlet
- Inspiratory and expiratory valves
- Breathing tube
- Reservoir bag
- Y-piece
- Pop-off valve
- Scavenging tubing
What is the pressure of the high pressure zone? Intermediate pressure? Low pressure?
High = 1900-2200 psi
Intermediate = 37-55 psi
Low = <30 cm H2O
What can be used to determine the volume of gas contained within the oxygen cylinder?
Pressure indicated on the cylinder pressure gauge
T/F: You can tell how much nitrous oxide is left in the tank by reading the pressure gauge.
False;
Nitrous oxide is partially stored in liquid form; P gauge reads 745 until all liquid is gone, and then you just have the gaseous form.
What are the possible cylinder sizes for oxygen?
E and H
What is the color for oxygen in the U.S.?
green
What is the capacity and pressure of an H tank?
6900 L
2200 psi
What is the capacity and pressure of an E tank?
660 L
1900 psi
What gas is denoted by yellow?
medical air
What gas is denoted by blue?
nitrous oxide
What is the diameter index safety system (DISS)?
Each plug has a different diameter and different thread to keep you from plugging in the wrong line.
What is the pin index safety system (PISS)?
2 holes on the cylinder stem, 2 holes on the yoke;
Unique pin location for each medical gas
What are the pin locations for oxygen? Air? Nitrous oxide?
Oxygen = 2, 5
Air = 1, 5
Nitrous oxide = 3, 5
Where is the regulator located?
Between high and intermediate pressure systems
What does the regulator do?
Reduces pressure from gas cylinder (1900-2200 psi) to working pressure (37-55 psi).
What does the flowmeter do?
Controls rate of medical gas passing through the vaporizer
Why is the flowmeter tube narrow at the bottom and wider at the top?
As the float moves up the tube, more gas can flow around the float, producing higher flow rates.
Flow rate is determined by position of _____.
the float
How is the flowmeter calibrated?
As a unit: flow tube, scale, and float
How would you read this?
At the center of the float = 2 L/min
How would you read this?
At the top of the float = 3 L/min
What is the flush valve used for?
Rapidly delivers large volumes (35-75 L/min) of oxygen to common gas outlet/breathing circuit;
Fills depleted reservoir bag, flushes out anesthetic gas in circuit
What area is the oxygen flush valve located in?
intermediate pressure
What does the oxygen flush valve bypass?
flowmeter and vaporizer
When is it never okay to use the oxygen flush valve?
When the patient is connected to the breathing circuit
What does the vaporizer do?
Converts liquid anesthetic into vapor and adds measured amount of the vapor to flow of gases going to patient
What two ways can gas go?
- Can bypass liquid anesthetic
- Can go into vaporizing chamber and pick up vapor molecules –> meets with bypass chamber –> common gas outlet
Where in relation to the breathing circuit is the vaporizer located in modern systems?
Outside the circuit (high-resistance)
What is the method of regulating output concentration in a modern vaporizer?
Precision/concentration-calibrated, variable bypass
What is the method of vaporization in a modern vaporizer?
Flow-over the wick
Vaporizers have _____ filling systems.
keyed
Where is the vaporizer in this system?
Out of circuit (VOC)
Where is the vaporizer in this system?
In the circuit (VIC)
VOC have a _____ construction.
complex
VOC have a _____ resistance to breathing.
high
What provides the carrier gas in a VOC?
fresh gas inflow
T/F: In a VOC, vaporizer output is not affected by patient’s ventilation
True
Which vaporizer is a precision vaporizer?
VOC
VOCs are inhalant agent _____.
specific
VOCs are _____ flow rate compensated.
temp/oxygen
Where are VICs located?
On inspiratory arm of the circle system
VICs have _____ construction.
simple
VICs have _____ resistance to breathing.
low
What provides the carrier gas in a VIC?
Inspiratory patient air flow
What inhalants can be used with a VIC?
multiple
Which vaporizer is a non-precision vaporizer? What does this mean?
VIC;
Anesthetic [] is unknown
What is the common (fresh) gas outlet?
Receives all gases and vapors from the machine and delivers mixture to breathing system.
The common gas outlet is a common location for _____; machines should be checked for _____ before each procedure.
disconnection, leaks
What are the functions of a breathing system?
- Allows fresh gas and inhalant to be delivered from the machine to the patient
- Eliminates the patient’s expired CO2 to scavenger
What does a breathing system consist of?
Breathing hose, reservoir bag, pressure relief valve
What are the 2 types of breathing systems?
Rebreathing and non-rebreathing (NRB)
What is the purpose of one-way valves in a circle system?
Used to produce unidirectional flow of gas through system
Where does expired gas go in a circle system?
It is recycled back into system
Where does expired CO2 go in a circle system?
Removed by CO2 absorbent
What is the resistance in a circle system vs. a NRB?
It is higher in a circle system
What is the ideal oxygen flow rate in a circle system?
30 mL/kg/min
What is the Y-piece?
Connects endotracheal tube to breathing hoses of the rebreathing system
Gases in the inspiratory tube are directed _____ patient on inspiration.
toward
Gases in expiratory tube are directed _____ patient on expiration.
away from
What happens to air flow if one of the valves in a circle system do not work?
Gas will not move in a circular fashion
What is the fresh gas inlet?
Site of delivery of oxygen and anesthetic gas from common gas outlet of machine to the breathing system.
Where is the fresh gas inlet located?
After CO2 absorbent and before inspiratory one-way valve
What does the breathing circuit pressure manometer indicate?
P within breathing circuit
Peak inspiratory pressure should not exceed _____ in small patients.
15-20 cmH2O
What can the breathing circuit pressure manometer be used for?
To check for leaks in the machine and around the endotracheal cuff
How is a leak test performed?
- Make sure all gas flows are set to 0
- Close pop-off valve and occlude Y-piece
- Turn flowmeter on and pressurize breathing system to 30 cmH2O
- Turn flowmeter off
- Do not use oxygen flush valve to completely inflate the reservoir bag
- P should not fall more than 10 cmH2O within 30 sec
- Open pop-off valve
Where are common areas for leaks?
Reservoir bag, breathing hose, CO2 absorbent canister, vaporizer
What is the recommended volume for a reservoir bag?
5-10 times patient’s tidal volume;
10-15 mL/kg
What can happen if the reservoir bag is too large?
Can be difficult to observe respiration, and result in slower rates of change in anesthetic [] when vaporizer output changed (circle system)
What can happen if the reservoir bag is too small?
Inadequate gas supply to meet peak inspiratory volume, unable to provide safety margin against P buildup within breathing system
The pop-off valve is on the _____ side of the circuit.
expiratory
What is the purpose of the pop-off valve?
Allows exhaled gases, waste gas, unused fresh gas to exit the circuit –> scavenger system
What is the P required to open the pop-off valve?
1-2 cmH2O
What can a completely closed pop off valve lead to?
Patient barotrauma or death
What does the scavenging system do?
Removes waste gases from the immediate workspace
In a passive system, where are waste gases diverted to and how?
To vent leading to outside work area by a hose connected to the APL
What is used to inactivate halogenated anesthetics in a passive scavenging system?
Activated charcoal canister
When are activated charcoal canisters changed?
When they gain 50g since before the first use
How does an active scavenging system work?
Vacuum pump creates negative pressure to collect waste gas
Active scavenging systems are more _____ and _____ to set up than passive systems.
complicated, expensive
What is the most common CO2 absorbent?
Soda lime
What is the makeup of soda lime?
80% calcium hydroxide
15% water
4% sodium hydroxide
How does a soda lime absorbent work?
CO2 passes thru soda lime –> forms calcium carbonate –> ethyl violet in absorbent changes color as the pH changes
When should absorbent be changed?
Observe at end of surgery and change if 1/3 violet
How is CO2 eliminated in a NRB?
By high fresh gas flows
What is the ideal oxygen flow rate in a NRB?
200 mL/kg/min
Where does inhaled gas pass through in a NRB?
Inner tube
Where does exhaled gas pass through in a NRB?
outer tube
What is the purpose of an endotracheal tube?
Transfers oxygen and inhalant from anesthetic machine into patient’s lungs
ET tubes help to maintain a _____ airway.
patent
ET tubes help facilitate _____ _____ ventilation.
positive pressure
ET tubes protect the lungs from _____.
aspiration
ET tubes help prevent _____ of work environment.
contamination
What are the main parts of an ET tube?
Murphy eye, radiopaque marker line, pilot balloon, adapter
What is the purpose of the Murphy eye?
It is useful if the tube is obstructed against tissue or something else;
Provides another way for the gas to flow in and out
What size ET tube should be used?
Largest that will fit without causing trauma
ETT size can be based on width of _____ _____.
nasal septum
Other than the nasal septum width, how else can you estimate ETT size?
Palpate the cervical trachea
How many ETTs should you have available?
min of 3
How is the length of the ETT measured?
From tip of patient’s shoulder to tip of the nose (minimize mechanical dead space)
What is a high-volume, low-pressure cuff?
Tracheal wall pressure is similar to intracuff pressure
What is a low-volume, high-pressure cuff?
Better protection against aspiration; intracuff pressure does not equal tracheal wall pressure
What do tracheal pressures >48 cmH2O do?
impede capillary blood flow
What do tracheal pressures <15 cmH2O do?
Increase risk of aspiration
When are guarded tubes useful?
In procedures where the ETT is likely to be compressed/kinked
What are disadvantages that occur when there is a leaky cuff?
Airway not protected from aspiration, difficult to keep patient anesthetized, pollutes environment
How is a cuff tested for proper inflation?
Administer least amount of air to inflate cuff and provide airtight seal so there is no leak when manual breath is given at 15-20 cmH2O
What can an excessive pressure in the cuff lead to?
tracheal necrosis
What does SGAD stand for?
supraglottic airway device
What does LMA stand for?
laryngeal mask airway
What are 2 alternatives to tracheal intubation?
SGADs and LMAs
What spp can SGADs and LMAs be used in?
cats and rabbits
SGADs and LMAs do not enter _____ or _____.
larynx, trachea
SGADs and LMAs form a seal around the _____.
glottis
Where should a laryngoscope be positioned?
At the base of the tongue, under the epiglottis, push down and pull forward
What is a ventilator?
Device designed to provide/augment patient ventilation;
Controls rate, volume/pressure, inspiratory/expiratory time of each breath
What replaces the rebreathing bag in a ventilator?
Bellows
What respiration phase occurs when the ventilator bellows collapse?
inspiratory
What respiration phase occurs when the ventilator bellows expand?
expiration
What is the suggested ventilator setting in small animals? Horses?
SA = 8-15 bpm with inspiratory time <1 second
Horses = 6-10 bmp with inspiratory time 1-2 seconds (peak P 20-30 cmH2O)
What are CV effects of IPPV?
Decreased venous return/CO/BP
What type of system do induction chambers connect to?
NRB
What is the FIO2 provided by masks?
35-60%
Why should you not force a face mask onto a struggling patient?
It increases patient’s metabolic oxygen consumption
What is a disadvantage of using a face mask?
Do not have an airway
What is a closed circle breathing system?
Uses absolute minimum oxygen flow rate to meet patient’s metabolic oxygen requirements
We don’t use this
What is the flow rate for a closed system?
3-5 ml/kg/min
What is the flow rate for a semi-closed system?
50-100 ml/kg/min initially;
20-30 ml/kg/min maintenance
What is the flow rate for a NRB system? Why is this necessary?
200 mL/kg/min;
High rate necessary to ensure expired gases not re-breathed
