Anesthesia Machine/Delivery Systems

Question 1

Name the components of the anesthesia workstation

Answer 1

◾Anesthesia machine ◾Vaporizers ◾Ventilator ◾Breathing circuit ◾Scavenging system ◾Monitoring system

Question 2

What is the high pressure circuit?

Answer 2

Cylinders (typically E-cylinders) and primary pressure regulator. O2 - up to 2200 psi N2O - up to 745 psi

Question 3

What is the intermediate pressure circuit?

Answer 3

Pipeline sources (50-55 psi), down-regulated cylinder sources (45psi)

Question 4

What is the function of a pressure regulator?

Answer 4

Reduce gas pressure from variable pressure cylinders to a consistent 45psi Some machines have a second stage O2 pressure regulator to further decrease oxygen pressure within the machine to a set pressure (12-19psi)

Question 5

When are the cylinders utilized?

Answer 5

When pressure within the machine drops below 45psi

Question 6

What is the function of the fail-safe valve?

Answer 6

on each NON-O2 gas line Shut off or decrease supply pressure (oxygen failure protection device) of all other gases if O2 line pressure falls to 28psi Prevents delivery of gas is O2 supply fails

Question 7

What is the low pressure circuit?

Answer 7

Machine from flow-control valves –> common gas outlet, including vaporizers

Question 8

What is the flow of oxygen delivered when using the oxygen flush valve?

Answer 8

100% O2 @ 35-75L/min at 50psi

Question 9

What is the color code for the following medical gases in the US: Oxygen Nitrous oxide Air CO2 Nitrogen

Answer 9

Oxygen = green Nitrous oxide = blue Air = yellow CO2 = grey Nitrogen = black

Question 10

What is the only monitor that detects problems/hypoxic mixture downstream of the flow control valves (low pressure circuit)?

Answer 10

Oxygen analyzer = one of the most important monitors

Question 11

Why is oxygen the last gas in the sequence of flow meters?

Answer 11

If one of the other gases leaks, its position is the least likely to result in hypoxic mixture

Question 12

What is the proportioning system on the anesthesia machine?

Answer 12

aims to prevent delivery of hypoxic mixtures Nitrous and O2 intercede mechanically and pneumatically to minimum [O2] at common gas outlet is 23-25%

Question 13

What are the limitations of the fail-safe system?

Answer 13

Only reads pressures. If gas pipelines are crossed - may allow hypoxic mixture

Question 14

What 3 things can fool the proportion limiting systems?

Answer 14

1. wrong supply gas 2. defective pneumatics or mechanics 3. leaks downstream

Question 15

How are flowmeters calibrated?

Answer 15

specifically for each gas based on density and viscosity of the gas

Question 16

What should you do if the oxygen low pressure alarm sounds?

Answer 16

• indicates profound loss of O2 pipeline pressure –> fully open E-cylinder + disconnect pipeline and consider use of low fresh gas flows

Question 17

Describe a non-rebreathing system

Answer 17

no rebreathing of exhaled gases ◾Reliable control of the inspired [gas] ◾Elimination of CO2 by venting all expired gases from the system. ◾High flow rates (equal to or more than the patient’s minute ventilation) must be supplied to the patient to prevent rebreathing, and so they are less economical to use. ◾Operating room environmental pollution is a problem. ◾Examples = AMBU bag, and the Mapleson Non-Rebreathing Circuits (Classification A-F).

Question 18

Describe a partial rebreathing system

Answer 18

partial recirculation of exhaled gas ◾most commonly used partial rebreathing configuration ◾circular flow of gases, separation of inspiratory and expiratory channels, unidirectional valves and carbon dioxide absorbers. ◾Mapleson Systems can also behave as partial rebreathing systems at low fresh gas flow (FGF) rates; however there is risk of rebreathing exhaled CO2 since there are no unidirectional valves, no clear separation of inspired and expired gases and no CO2 absorbers.

Question 19

Describe a complete rebreathing system

Answer 19

inflow gas exactly matches consumption by the patient In a closed system - complete rebreathing of exhaled gases after absorption of CO2. A circle system can be used in a closed configuration at extremely low fresh gas flows.

Question 20

What are the major components of a classic circle system?

Answer 20

◾Fresh gas inflow site (best downstream of CO2 abs b4 inspiratory uni-valve) ◾Inspiratory and expiratory limbs ◾Inspiratory and expiratory unidirectional valves ◾Y-Piece ◾Reservoir bag ◾Ventilator ◾Bag/ventilator selector switch ◾Carbon dioxide absorber ◾Adjustable pressure limiting (APL) valve ◾Air pressure monitor gauge ◾Spirometer Optional: ◾Positive end expiratory pressure (PEEP) valve ◾Filters ◾Heated humidifier ◾Respiratory gas monitor sensor / gas sampling line.

Question 21

How does a CO2 absorber work?

Answer 21

CO2 + water –> carbonic acid + calcium hydroxide –> carbonate, water and heat Contains silica –> less likely to disintegrate –> dec breathing system resistance pH indicator to highlight exhaustion (ethyl violet)

Question 22

What are the two types of absorbents?

Answer 22

1. High alkali absorbents (#1) 2. Alkali-free absorbents

Question 23

Describe the high alkali absorbents

Answer 23

Soda lime formulations Mixture of calcium hydroxide (CaOH2) 75%, water 20%, sodium hydroxide (NaOH) 3%, potassium hydroxide (KOH) 1% When dessicated, they react w/ volatile anesthetics –> CO Compound A formation with Sevo

Question 24

Describe the alkali free absorbents

Answer 24

Calcium hydroxide No CO formation No compound A formation

Question 25

List 3 ways to identify when it is time to change the absorbent

Answer 25

1. CO2 in the inspired gas is the most reliable method 2.Indicator pH dye color change. Certain absorbents with high alkali content (sodium and potassium hydroxide) may show color reversal (peaking and regeneration phenomenon) if the absorbent is allowed to rest. However, when this happens, the absorbent is generally near exhaustion and the exhausted color will reappear after just brief exposure to carbon dioxide 3.Excessive heat production, especially on the downstream side of the canister is also an indication that the absorbent is nearing exhaustion, and usually starts to occur before color change.

Question 26

List 3 desirable characteristics of a pediatric circle breathing system

Answer 26

1. Shorter, narrow-caliber hoses minimize compliance loss 2. Split Y-pieces dec dead space 3. Smaller CO2 absorbers decrease system resistance

Question 27

What are the advantages of a closed circuit?

Answer 27

1. Economy: significant savings can be achieved with lower flows of gases 2. Reduced operating room pollution with lower flows. Since less volatile agent is used, vaporizers are filled less frequently. 3. Estimation of anesthetic agent uptake and oxygen consumption: in a closed system the fresh gas flow is matched by the patient’s uptake of oxygen and anesthetic agents. 4.Heat and humidity conservation: lower gas flows, inspired humidity increased, and rate of fall in body temperature reduced.

Question 28

What are the disadvantages of a closed circuit?

Answer 28

1. More attention required: fresh gas flow into system must be kept in balance with uptake = frequent adjustments. 2.Inability to alter inspired concentrations quickly: the use of low fresh gas flows prevents the rapid change in fresh gas concentration in the breathing system that occurs with high gas flows. 3.Danger of hypercarbia: resulting from exhausted absorbent or incompetent unidirectional valves greater when low flows are used. 4.Accumulation of undesirable gases in the system: a.Carbon Monoxide: from the interaction of desiccated absorbent and anesthetic. b.Acetone, methane, hydrogen, and ethanol: accumulate during closed system anesthesia. dangerous only after hours of closed system anesthesia. c.Compound A: The safety of using sevoflurane with low flows is still under investigation. The FDA still recommends that sevoflurane not be used with fresh gas flows of less than 2 L/minute. 5.Uncertainty about inspired concentrations: one of the effects of rebreathing is that the inspired concentrations cannot be accurately predicted. 6.Faster absorbent exhaustion: the lower the fresh gas flow, the faster the absorbent is exhausted.

Question 29

In the Mapleson A circuit, which mode of ventilation requires the highest fresh gas flow, spontaneous or controlled?

Answer 29

Controlled = A (>3MV)

Question 30

What 2 components are closest to the patient in Mapleson B & C circuits?

Answer 30

APL and FGF

Question 31

What Mapleson system is most efficient in terms of FGF during controlled ventilation?

Answer 31

D (1-2x MV) (Equal to Bain system)

Question 32

How is a Mapleson F different from an E circuit?

Answer 32

E + open-ended bag added Positive pressure breaths can be given w/ control of pressures (vs. occluding corrugated tubing in E-circuit)

Question 33

In the Bain circuit, what is the potential advantage of inner FGF tubing being surrounded by exhaled gases in corrugated tubing?

Answer 33

Like Mapleson D *May warm FGF*

Question 34

How are connectors used in anesthesia breathing circuits?

Answer 34

join various components of the circuit together

Question 35

What is an adapter and how is it different from a connector?

Answer 35

takes one part of a circuit and adapts it to connect to a different part, or for a different use - give albuterol - insert bronchoscope

Question 36

List several signs of facemark leak

Answer 36

1. lack of chest movement with positive pressure ventilation 2. audible leaks around the mask 3. truncated or absent capnograph tracing

Question 37

What is a sign of damage to the corrugated tubing?

Answer 37

Air leak

Question 38

What would happen if both unidirectional valves were stuck open?

Answer 38

rebreathing of CO2 –> potential hypercapnea

Question 39

What would happen if both unidirectional valves were stuck closed?

Answer 39

circuit becomes completely occluded

Question 40

What would happen if the expiratory valve was stuck open?

Answer 40

capnogram may not return to baseline on the capnograph (this would also lead to rebreathing of carbon dioxide)

Question 41

What would happen if the expiratory valve was stuck closed?

Answer 41

breath-stacking (inspiration prior to the complete exhalation of the previous breath) –> volutrauma or barotrauma hypotension d/t dec VR

Question 42

What is the function of the APL valve?

Answer 42

vents off excess gas and prevents accumulation of excessive pressure within the breathing circuit (=airway)

Question 43

In a closed breathing system, what position must the APL valve be in?

Answer 43

APL must be closed (inflow of gas = consumed by pt)