Anesthesia Lab 1 - Machines Flashcards
What are the 5 basic components of an anesthetic machine?
- Flowmeter
- Regulator
- Vaporizer
- Gas supply
- Scavenging system
1
Flowmeter
2
Vaporizer
3
fresh gas outlet
4
O2 flush valve
5
oxygen/gas supply
6
hanger yoke
7
regulator
8
pressure gauge for e-tank
9
gas line
10
waste gas line
What is the purpose of the anesthetic machine and the breathing circuit?
To deliver oxygen and inhalant anesthetic to the patient and remove CO2
What are 2 possible sources for the medical gas supply to the anesthetic machine?
- Local portable source (cylinder)
- Pipeline source (central gas supply)
What does the gas supply do other than provide oxygen to the patient?
Acts as a carrier for the inhalant anesthetic and “carries” the inhalant from the machine and through the breathing circuit to the patient
What is the most common carrier gas? What other gas can be used?
Oxygen is most common but nitrous oxide can also be used
What is this?
Liquid oxygen tank
Where would the regulator be in this picture?
Under the white cover
What is the role of the pressure regulator?
Lowers psi from main tank (up to 2200 psi in an E tank) to a safer working pressure of ~50 psi and maintains constant outlet pressure up to flows of 15 L/min
Where is the regulator in this photo?
Where is the gauge that shows the pressure of oxygen in the H tank?
Where is the gauge that shoes the pressure of oxygen leaving the tank?
How do you turn on the oxygen tank attached to the anesthetic machine (E tank)?
Use wrench to slowly turn the valve counterclockwise with a 1/2 turn
How do you calculate how many liters of oxygen a tank contains?
Read the tank pressure and divide by 3 or multiply by 0.3
If you have a tank whose pressure gauge reads 1200 psi, how many liters of oxygen does the tank contain? How long would the tank last if you ran an oxygen flow of 2 L/min?
1200 psi x 0.3 = 400 L
400 L @ 2 L/min = 200 min (3h 20m)
What are the 2 features on the E tank intended to prevent accidental administration of the wrong gas to a patient?
PISS (Pin Index Safety System)
DISS (Diameter Index Safety System)
Can you leave a full or empty oxygen tank standing upright without restraining straps, chains, or other type of a storing rack?
HELL NO
If a full E cylinder of oxygen were to accidentally fall over and the valve stem at the top broke off, what would the tank do?
It would act as a missile and shoot away
What is the role of the flowmeter?
Used to control the amount of the medical gas which goes through the vaporizer and to the patient
What gas is the color green representing in the lab?
oxygen
Where do you read the oxygen flow in a flowmeter with a ball bobbin?
at the widest diameter of the ball
Where do you read the oxygen flow in a flow meter with a float bobbin?
At the top of the float
What does the oxygen flush valve do?
Allows the oxygen to bypass the vaporizer and flow directly through the common gas outlet and into the breathing circuit
Why is it dangerous to activate the oxygen flush valve if a patient is attached to the machine?
You would be giving oxygen at 35-75 L/min = too much
Why does the alarm on the back of the machine sound when the flush button is activated?
It is a warning in case the valve is accidentally pushed
What is the role of the vaporizer?
It is used to add a specific amount of inhalant anesthetic agent to the gas (oxygen) mixture in order to anesthetize the patient.
How is the amount of inhalant anesthetic expressed on the vaporizer?
As a % of the vapor output
What gases exit the common gas outlet when the vaporizer is off?
oxygen only
What gases exit the common gas outlet when the vaporizer is on?
oxygen and isoflurane (or whatever anesthetic is in use)
What are some health and safety concerns with waste gas exposure (inhalants, nitrous oxide)?
Can cause miscarriages, abortion, congenital defects, liver and kidney disease, cancer (nitrous oxide = teratogen)
What are the 2 general types of waste gas scavenging methods?
Passive and active
What are advantages and disadvantages of the passive scavenging system?
Advantage = easier to use
Disadvantages = less efficient after time, patient’s breathing is responsible for moving the gas down the tube, distance of tubing to the outside is likely to offer significant resistance to breathing
What are advantages and disadvantages of the active scavenging system?
Advantages = Complemented, more effective at waste removal
Disadvantages = more expensive and complicated to install
What scavenging system is this?
active
What scavenging system is this?
Passive
What is the purpose of a breathing circuit?
Allows inhalant gas (iso or sevo) and fresh gas (oxygen or nitrous oxide) to be delivered from the anesthetic machine to the patient and carries expired CO2 away from the patient
What are the 2 basic types of breathing circuits?
Rebreathing (circle), non-rebreathing
What is the difference between rebreathers and non-rebreathers with respect to carbon dioxide absorbent?
Rebreather = has absorbent
Non = does not have absorbent
What is the difference between rebreathers and non-rebreathers with respect to resistance to breathing? Why is this?
Rebreather = high –> due to complex structures in the air passage
Non = low –> simpler structure (few or no valves and less parts)
What is the difference between rebreathers and non-rebreathers with respect to required fresh gas (oxygen) flow rate?
Rebreather = low –> due to elimination of CO2 being accomplished with CO2 absorbents
Non = high –> due to absence of a CO2 absorbent
Which system better preserves heat and moisture from the patient?
Rebreathing circuit
Which system has a reduced cost to run?
Rebreathing circuit because it requires a reduced oxygen flow rate which reduces the cost of inhalant anesthetic agent
When would you use a NRB (weight)?
< 7 kg
When would you use a pediatric circle system (weight)?
7-12 or 15 kg
When would you use an adult circle system?
>12-15 kg
Reservoir/rebreathing bag should be ___ times the resting _____.
3-5, tidal volume
Reservoir bag size should be > or equal to ___ ml/kg.
50-60
What can happen if the reservoir bag is too small?
Patient may not be able to inspire its desired tidal volume
What can happen in the reservoir bag is too large?
It may be hard to visualize the breathing activity of the patient and the bag adds volume to the circuit, increasing the time constant
What is the Bain circuit?
NRB = co-axial “tube-within-a-tube”
What is the diameter of the pediatric circle hose?
13 mm
What is the diameter of the adult circle hose?
22 mm
What are the 6 steps to perform a positive pressure leak test on the machine?
- Close pop-off valve and occlude the Y piece with a thumb
- Fill reservoir bag by opening the flowmeter to 3.0 L/min while watching the P manometer on the machine
- Continue filling the bag until the manometer registers 20 cm H2O pressure and then shut off the flowmeter
- Watch the manometer - if the P remains constant for 10 seconds, then there are no leaks in the system
- If the P decreases, record how many cm H2O - if there is a leak, turn on the flowmeter and determine flow necessary to maintain a 20 cm H2O pressure
- Open pop-off valve and ensure the P returns to 0 and squeeze the resevoir bag to empty it into the scavenge system (DO NOT REMOVE THUMB FROM Y PIECE BEFORE OPENING THE POP-OFF VALVE)
T/F: In the NRB, there are no valves to prevent rebreathing of expired gases.
True
You have a 5.0 kg cat on a Bain co-axial NRB with a 0.5 L bag. What oxygen flow rate would you use immediately after induction?
(Flow rate avg for NRB = 200 ml/kg/min; minimum 0.5 L/min)
5.0 kg * 200 ml/kg/min = 1000 ml/min = 1.0 L/min
You have a 5.0 kg cat on a Bain co-axial NRB with a 0.5 L bag. What oxygen flow rate would you use for maintenance?
(Flow rate avg for NRB = 200 ml/kg/min; minimum 0.5 L/min)
5.0 kg * 200 ml/kg/min = 1000 ml/min = 1.0 L/min
,You have a 10 kg dog on a pediatric circle rebreathing system with a 1.0 L bag. What oxygen flow rate would you use immediately after induction?
(Semi-closed induction phase rate = 50-100 ml/kg/min, minimum 0.5 L/min, max 5.0 L/min)
10 kg * 50-100 ml/kg/min = 500-1000 ml/min = 0.5-1.0 L/min
You have a 10 kg dog on a pediatric circle rebreathing system with a 1.0 L bag. What oxygen flow rate would you use for maintenance?
(Semi-closed maintenance rate = 20-30 ml/kg/min, minimum 0.5 L/min, max max 5.0 L/min)
10 kg * 20-30 ml/kg/min = 200-300 ml/min = 0.2-0.3 L/min
Since the minimum flow meter setting for a rebreathing system is 0.5 L/min, we must use 0.5 L/min for this patient.
You have a 30 kg dog on an adult circle rebreathing system with a 3.0 L bag. What oxygen flow rate would you use immediately after induction?
(Semi-closed induction phase rate = 50-100 ml/kg/min, minimum 0.5 L/min, max 5.0 L/min)
30 kg * 50-100 ml/kg/min = 1500-3000 ml/min = 1.5-3.0 L/min
You have a 30 kg dog on an adult circle rebreathing system with a 3.0 L bag. What oxygen flow rate would you use for maintenance?
(Semi-closed induction phase rate = 50-100 ml/kg/min, minimum 0.5 L/min, max 5.0 L/min)
30 kg * 20-30 ml/kg/min = 600-900 ml/min = 0.6-0.9 L/min
You have a 500 kg horse on a large animal rebreathing system with a 30 L bag. What oxygen flow rate would you use immediately after induction?
(Rate for induction phase = 20 ml/kg/min; max is 10 L/min)
500 kg * 20 ml/kg/min = 10,000 ml/min = 10.0 L/min
You have a 500 kg horse on a large animal rebreathing system with a 30 L bag. What oxygen flow rate would you use for maintenance?
(Rate for maintenance = 10 ml/kg/min; max is 10 L/min)
500 kg * 10 ml/kg/min = 5000 ml/min = 5.0 L/min
What does the time constant tell the anesthetist?
How long it will take for a change in anesthetic [] to occur.
If you change the vaporizer setting to make a change in the inhalant % entering the breathing circuit, ___% of that change will occur in 1 time constant.
63%
How is time constant calculated?
Total volume in breathing circuit (in L) / oxygen gas flow rate (L/min)
Time constant = Volume / Flow
When the vaporizer dial setting is changed, it takes ___ time constants to effect a 99% change in circuit [].
5
If a circuit has a total volume of ~6 L and the gas flow rate is 2 L/min, what is the time constant?
How long would it take for the anesthetic [] in the circuit to reach 99% of the new dial setting if it were to be changed?
TC = vol/flow = 6L / 2 L/min = 3 min
Would take TC x 5 = 3 min x 5 = 15 min to reach 99%
What are two ways to change the anesthetic [] more rapidly and which way is used in large vs. small animals?
- Turn up fresh gas flow rate = small animals
- Make big change in the vaporizer dial setting (“over-pressure”) = large animals
A small animal machine has adult breathing hoses (1.0 L), soda lime canister (2.0 L), and a 5 L reservoir bag. The oxygen flowmeter is set on 1 L/min. What is the time constant?
1.0 L + 2.0 L + 5.0 L = 8.0 L = total volume of the system
TC = volume/flow = 8.0 L / 1 L/min = 8 min
A small animal machine has adult breathing hoses (1.0 L), soda lime canister (2.0 L), and a 5 L reservoir bag. The oxygen flowmeter is set on 1 L/min.
If the vaporizer setting is changed from 1% to 2%, how long will it take to achieve 99% of that change in the rebreathing system?
TC = 8 minutes
8 min x 5 = 40 minutes
You have a cat in an induction box and want to induce anesthesia. You will need to achieve 3% isofurane in the box to accomplish this. The volume of the chamber is 20 L, the vaporizer is set to 3%, and the oxygen flow meter is 2 L/min.
How long will it take to achieve 3% isoflurane in the chamber?
TC = volume / flow = 20 L / 2 L/min = 10 minutes
You have a cat in an induction box and want to induce anesthesia. You will need to achieve 3% isofurane in the box to accomplish this. The volume of the chamber is 20 L, the vaporizer is set to 3%, and the oxygen flow meter is 2.0 L/min.
You don’t have time to waste so you put the vaporizer on 5% and the oxygen flow meter on 5.0 L/min. How long would it take to reach 3% isoflurane in the chamber?
TC = volume / flow = 20 L / 5.0 L/min = 4 minutes
Takes 5 TC (20 min) to achieve 99% of 5% isoflurane
3% iso is 60% of 5% iso
1 TC = 63% effect –> just under 4 min (~3.8 min)
You are anesthetizing a 500 kg horse on a large animal anesthetic machine with a 30 L reservoir bag, 10 L soda sorb canister, and breathing hoses with 10 L volume. The flow meter is set on 10 L/min.
What is the time constant?
30 L + 10 L + 10 L = 50 L total volume
TC = volume/flow = 50 L / 10 L/min = 5 minutes
You are anesthetizing a 500 kg horse on a large animal anesthetic machine with a 30 L reservoir bag, 10 L soda sorb canister, and breathing hoses with 10 L volume. The flow meter is set on 10 L/min.
If we turn the isoflurane to 2% right after induction, how long will it take to achieve that [] in the system?
TC = 5 minutes
5 min x 5 = 25 min
You are using a NRB to deliver anesthesia to a 5 kg cat with an oxygen flow meter setting of 1 L/min. The reservoir bag is 1 L and the breathing system is < 1 L.
What is the time constant?
TC = volume / flow = < 1 L / 1 L/min = < 1 min
This is a NRB so there is no dilution, therefore virtually no TC;
Patient inspires the % set on the vaporizer almost immediately
An anesthetized dog is attached to a machine and breathing system with a volume of 5 L. It’s time to wake the dog up so you turn the vaporizer to zero but leave the oxygen flow meter at 1 L/min.
Why do we want to do this?
We rarely allow a small animal patient to breathe room air right away because of the respiratory depression of the inhalant anesthetic - it can lead to hypoxia and it is a good idea to scavenge the exhaled anesthetic gas during the initial part of recovery.
A general rule is to give the small animal patients ___ min of oxygen before disconnecting them from the anesthetic machine.
10
An anesthetized dog is attached to a machine and breathing system with a volume of 5 L. It’s time to wake the dog up so you turn the vaporizer to zero but leave the oxygen flow meter at 1 L/min.
How long will it take to ahcieve a zero [] of isoflurane in the system with a flow meter setting of 1 L/min?
TC = volume/flow = 5 L / 1 L/min = 5 minutes
An anesthetized dog is attached to a machine and breathing system with a volume of 5 L. It’s time to wake the dog up so you turn the vaporizer to zero but leave the oxygen flow meter at 1 L/min.
If you increase the flow meter setting to 5 L/min, how long will it take to achieve zero concentration of isoflurane in the system?
TC = volume/flow = 5 L / 5 L/min = 1 minute
If you want to make a quick change in the anesthetic gas [] in a rebreathing system what do you want to do to the time constant?
decrease it
What are 3 advantages and 1 disadvantage of using low oxygen flow rates for maintenance of inhalant anesthesia?
Adv = save resources, use less inhalant, pollute the world less
Disadv = result in a long TC
