Anesthetic Machine & Breathing Circuits

Question 1

What are the 4 primary functions of the anesthesia gas delivery system?

Answer 1

1. Provide O2 to the patient
2. To blend and deliver an anesthetic gas mixture
3. To remove CO2 from breathing circuit
4. To support ventilation of the patient

Question 2

Name the 4 component subsystems of the anesthesia machine

Answer 2

High pressure system, low-pressure system, breathing system, and scavenging system

Question 3

The role of the high-pressure system is to…?

Answer 3

regulate pressure before the gas enters the low-pressure system

Question 4

What is the role of the low-pressure system?

Answer 4

it is where O2 and the anesthetic gas mixture are mixed

Question 5

What does the breathing system do?

Answer 5

delivers the anesthetic gas mixture to the patient

Question 6

What is the purpose of the scavenging system?

Answer 6

collects excess gas from the breathing system and transports it to the waste gas evacuation system

Question 7

What is a pipeline gas supply and how might it differ in a large hospital vs. private practice?

Answer 7

anesthetic machine receives its gas supply (typically O2) from this via high-pressure gas hoses; central supply of liquid O2 (large hospital) vs. series of O2 tanks stored at back of private practice

Question 8

What is the operating pressure of the pipeline gas supply?

Answer 8

50-55 psig (pounds per square inch)

Question 9

What is the formula to determine the volume of oxygen in an E-cylinder based on the pressure gauge reading?

Answer 9

Multiply the pressure gauge by 0.3

Question 10

Why is liquid O2 preferable to gaseous and and what temperature is it stored?

Answer 10

less expensive and large amounts of oxygen can be stored at one time; -297 degrees F

Question 11

Why is N₂O no longer used in vet clinics?

Answer 11

too great of a potential for abuse

Question 12

What is the general purpose of the safety features installed in a high pressure system?

Answer 12

to prevent delivery of hypoxic gas to patient

Question 13

Describe the Diameter Index Safety System (DISS)

Answer 13

• prevents misconnection of a gas supply hose to the wrong pipeline gas inlet e.g different sized body, nipple, nut

Question 14

What are quick connectors?

Answer 14

allow faster connection of gas supply hoses to the pipeline outlets than DISS connectors; based on matching pins and holes

Question 15

Pin Index Safety System (PISS) Connections

Answer 15

use unique pin and receptacle combos on cylinder hanger yokes to prevent misconnection of gas cylinder to wrong cylinder inlet

Question 16

What is the purpose of the pressure regulator? And what pressure does it reduce that of the E-tank to?

Answer 16

allows maintenance of constant flow as cylinder pressure changes, which prevents flowmeter fluctuation; 45 psig

Question 17

What are the different safety features of the high pressure system?

Answer 17

1. Diameter Index Safety System connections
2. Quick connectors
3. Pin Index Safety System connections
4. Pressure regulator
5. Flow control valves

Question 18

Why should you not interchange the flowmeters from different machines?

Answer 18

because the floats and flow tubes are calibrated as a pair for a specific gas

Question 19

How should you read the indicator of a flowmeter differently for an indicator that is a ball vs. one that is not?

Answer 19

you read the ball indicator in the center, all others are read at the top

Question 20

What is the purpose of a manifold and why do we not use it in vet med?

Answer 20

it is the junction where gas emerging from each flow meter must be joined together; we only use O2 in vet med

Question 21

What is the function of the vaporizer in the low-pressure system?

Answer 21

facilitates the change of a liquid anesthetic into its vapor and add a controlled amount of this vapor to the fresh gas flow

Question 22

What are the features of a precision vaporizer?

Answer 22

• a portion of O2 flow passes through the vaporizing chamber (contains liquid anesthetic) and another portion bypasses. The gases remix prior to exiting to provide desired anesthetic concentration
• placed out of breathing circuit to prevent breathing resistance

Question 23

What is the purpose of the oxygen flush valve and when should and shouldn’t it be used?

Answer 23

provides direct connection b/t high pressure and breathing systems (bypassing the vaporizer)

should use: in recovery when using a rebreathing system to rapidly replace gas in breathing bag

should NOT use: when using non-rebreathing system and when starting inhalation anesthesia b/c can dilute anesthetic concentration or could overpressurize lungs

Question 24

Define an open breathing system

Answer 24

no reservoir for anesthetic gas mixture and no rebreathing of expired gas; e.g. ‘open drop’

Question 25

Define a semiopen breathing system

Answer 25

with **reservoir** for anesthetic gas mixture, no rebreathing of expired gas, and **without CO₂ absorption**; e.g. non-rebreathing systems (Jackson-Rees)

Question 26

What is a semiclosed breathing system?

Answer 26

with reservoir for anesthetic gas mixture, **partial rebreathing** of expired gas, and **with CO₂ absorption;** e.g. circle

Question 27

Define a closed breathing system

Answer 27

with reservoir for anesthetic gas mixture, complete rebreathing of expired gas without CO₂ (removed by soda lime/baralyme); **O₂ supplied to patient is equal to its metabolic requirement**

Question 28

What are the two main breathing systems utilized in veterinary practice?

Answer 28

1. circle breathing systems (semiclosed) 2. non-rebreathing systems (semiopen)

Question 29

What are the components of a circle breathing system?

Answer 29

1. CO2 absorber 2. Unidirectional valves 3. Breathing (reservoir) bag 4. Breathing tubes and Y-piece 5. Pressure gauge 6. Negative pressure relief valve 7. Adjustable pressure limiting valve (pop off valve)

Question 30

The main capacity for CO₂ absorption of soda lime is

Answer 30

Ca(OH)₂

Question 31

Why is water needed in the soda lime reaction occurring in the CO₂ absorber?

Answer 31

CO₂ must be dissolved before it can react

Question 32

What are the characteristics of fresh soda lime?

Answer 32

* crumbles easily * white * CO₂ canister feels warm during anesthesia * Bitter taste

Question 33

What are your 4 indicators that your soda lime is "old" or exhausted?

Answer 33

* hard and chalky * color turns blue/violet with exhaustion * CO₂ canister stays cool during anesthesia * Slightly salty taste

Question 34

What is the formula to determine breathing bag size?

Answer 34

6 x tidal volume (10-15 ml/kg)

Question 35

T or F: a circle rebreathing system can operate without a pressure gauge?

Answer 35

True

Question 36

What is the purpose of the negative pressure relief valve?

Answer 36

allows entry of room air into the circuit when there is an excessive negative pressure in the circuit as a result of the patient inspiring from an "empty" circuit (\*no longer on VAB machines)

Question 37

What are the advantages of using a vaporizer out of the circuit?

Answer 37

1. Vaporizer output isn't affected by changes in ventilation 2. Assisted or controlled ventilation will not greatly increase inspired anesthetic concentration 3. Known anesthetic concentration can be delivered to the patient breathing circuit 4. Inspired gas, esp at low fresh gas flow, is humidified resulting in decreased loss of patient's body heat

Question 38

Disadvantages of using a vaporizer out of the circuit?

Answer 38

1. $$$ 2. Slow changes in anesthetic concentration because the expired gas dilutes anesthetic concentration in the breathing circuit

Question 39

Why do you increase O2 flow rate from 1 L/min to 2-3 L/min immediately after anesthetic induction using an IV agent?

Answer 39

the higher flow rate minimizes the difference between inspired anesthetic concentration and the concentration set at the vaporizer, which will expedite the induction process

Question 40

What are a couple problems associated with circle breathing systems?

Answer 40

1. resistance to breathing d/t the unidirectional valves and CO2 canister 2. dead space - mainly d/t the Y piece Both of these prove much more problematic in smaller patients

Question 41

Name the 2 benefits of using a non-rebreathing system?

Answer 41

1. Provides less dead space\* 2. Provide less or no resistance to breathing\* \*compared to circle breathing systems

Question 42

Describe the Jackson-Rees non-rebreathing system

Answer 42

* the patient inspires fresh gas from the expiratory tube and the fresh gas inlet. * During expiration, expired gas goes down the expiratory tube. * During the expiratory pause, CO₂ exhaled by the patient is eliminated by the high fresh gas flow via the outflow valve.

Question 43

What gas flow rate do people generally use?

Answer 43

200-300 ml/kg/min

Question 44

What are the advantages of non-rebreathing systems?

Answer 44

* no valves, so low resistance * good control of anesthetic concentration which means the inspired anesthetic concentration is the concentration set on the vaporizer * less dead space

Question 45

What are the disadvantages of the non-rebreathing system?

Answer 45

* very high gas flow needed in mL/kg/min and higher anesthetic consumption especially in bigger animals * inspired gas is not humidified - leads to greater loss of body heat * more pollution of the environment

Question 46

What is the Bain Coaxial System?

Answer 46

* a modified Mapleson D system - most common non-rebreathing system used in UF SAH * internal tube supplies fresh gases to patient end of system **minimizes mechanical dead space** * inspires fresh gas from large bore, expiratory and inspiratory tubes, and expired gas is directed down expiratory tube and _flushed out by high flow of fresh gas during expiratory pause_

Question 47

What 3 elements make up the scavenging system?

Answer 47

1. Gas collecting assembly 2. Interface 3. Disposal system

Question 48

What is the purpose of the interface in the scavenging system?

Answer 48

* prevents transfer of pressure changes in the scavenging system to the breathing system * provides postive pressure relief to protect patient from occlusions of scavenging system * provides negative pressure relief to limit pressure effects of an active disposal system

Question 49

What is an active disposal system?

Answer 49

provides negative pressure to eliminate the waste gas e.g. piped vacuum and active duct systems (used at UF)

Question 50

What is a passive disposal system?

Answer 50

waste gas moves to disposal system w/o an aid of a system that provides negative pressure, e.g. nonrecirculating ventilation systems, piping directly into atmosphere and absorption devices (activated charcoal * used at UF when transporting a small anesthetized patient from one section of hospital to another