anesthesia breathing systems

Question 1

What is the breathing system?

Answer 1

links the patient to the anesthesia machine by delivering oxygen and anesthetic gases and eliminating carbon dioxide

Question 2

what are the types of breathing systems?

Answer 2

• resuscitation
• insufflation (open)
• open drop (open)
• draw over (semi open)
• maplesons (semi open)
• circle (semi closed or closed)

Question 3

all circuits have some resistance, how can circuit resistance be decreased?

Answer 3

• decrease in circuit length
• increase circuit diameter
• avoid sharp bends
• eliminating valves (cant totally eliminate, need unidirectional flow)
• maintaining laminar flow

Question 4

what happens when you have increased gas flows?

Answer 4

• decreased rebreathing (of O2, CO2, N2O, and volatile agent)
• decreased equilibration time between “dialed-in” concentration and inspired concentration

Question 5

when do you use high flows?

Answer 5

• for induction to denitrogenate and get inspired gas concentration up
• for emergence to “wash out” anesthetic gases
• to prevent rebreathing

Question 6

when do you use low flows?

Answer 6

-for maintenance to conserve heat, humidity, volatile agent, and minimize OR contamination

Question 7

describe resuscitation breathing system.

Answer 7

-use of ambu (artificial manual breathing unit) bag
-self refilling with O2 or room air
-valves help with one way flow
>pt valve opens on inspiration
>exhalation ports allow venting during exhalation
>nonrebreathing valve
>intake valve closes with compression allowing for + pressure
*needs high flows for high FiO2

Question 8

what are some advantages and disadvantages of the resuscitation breathing system?

Answer 8

• advantage: simple, portable, can deliver almost 100% O2
• disadvantage: difficult to determine mask to face seal
• • with anesthesia bag, if there is no seal, bag will go flat

Question 9

describe open-drop anesthesia breathing system.

Answer 9

-used ether or chloroform
-dripped onto gauze over a mask
-pt inhales -> air passing through vaporizes the liquid
agent -> mask gets cold -> condensation and decreased
vapor pressure
**completely open method, not in circuit, not controlled
*no longer used, historically important

Question 10

describe draw-over anesthesia breathing system.

Answer 10

• ambient air is inhaled (drawn over) liquid agent
• pt inhalation “draws over” the vaporizer
• can be fitted with valves for O2, positive pressure ventilation and passive scavenging
• *amt of O2 and gas given is dependent on flow and temp
• *semi open method
  ex: copper kettle

Question 11

how does flow affect amount of O2 and gas in draw-over anesthesia?

Answer 11

• 1 L/min O2- FiO2 30-40%

- 4 L/min O2- FiO2 60-80%

Question 12

what are the advantages of draw-over anesthesia?

Answer 12

• simple
• portable
• can be used without compressed gas or ventilators
• can be used with room air
• used in war zones

Question 13

what is insufflation?

Answer 13

blowing gas across the face

*more a technique than a breathing system

Question 14

what are some uses of insufflation?

Answer 14

• preoxygenation
• manual ventilation
• inhalation inductions (peds)
• under drapes during sedation
• flushed out CO2 but caused fires from accumulating O2
• apneic techniques
  
  • airway surgeries cant have something in airway, keeps O2
  • blowing O2 over airway, like with jet ventilators
  • does not help with CO2, just keeps Sat up
  • still have to take breaks & insert tube to blow off CO2

Question 15

describe Mapleson systems?

Answer 15

-breathing systems with components added
-location of components determines classification
(A-F)
*total nonrebreathing
*use high gas flows
-dangerous with potent gases
-flushes out pt. moisture and heat
-wastes gases and contaminates OR
**semi open

Question 16

how are Mapleson systems total nonrebreathing?

Answer 16

fresh gas comes in to patient during inhalation, exhalation goes out to APL valve to go to scavenging

Question 17

what are the components of the Mapleson system?

Answer 17

• breathing tube
• fresh gas inlet
• adjustable pressure-limiting (APL) valve
• reservoir bag

Question 18

describe the Mapleson breathing tube.

Answer 18

• corrugated (rubber or disposable synthetic)
• large (22mm) diameter for low resistance
• long tubes and/or high compliance equal large gradient b/w gas delivery to circuit and gas delivery to pt (takes longer)

Question 19

describe the Mapleson fresh gas inlet.

Answer 19

• anesthetic gases (volatiles, N2O, O2, air) from anesthesia machine enter the Mapleson through the FGI
• location of FGI determines class

Question 20

describe the APL valve or “pop-off” of the Mapleson system.

Answer 20

• controls pressure build up in the circuit (vents/pops off when a set pressure is reached)
• APL vents from circuit to scavenging system

Question 21

describe the reservoir bag in the Mapleson system.

Answer 21

• 2 functions
  1) anesthetic gas reservoir
  2) positive pressure ventilation manually
• protective from barotrauma (as volume increases, compliance increases; wont keep getting bigger so won’t back up pressure to pt)

Question 22

what are the Mapleson characteristics?

Answer 22

• high flows to prevent rebreathing
• with spontaneous ventilation: fgf MUST equal minute ventilation (have to match how much they are taking in)
• with controlled + pressure ventilation (mechanical or manual): fgf must be 3x minute ventilation

Question 23

what is the Bain Circuit?

Answer 23

a type of Mapleson D with the fresh gas inlet tube inside the corrugated tubing

• “tube in a tube”
• preserves some heat
• still used in some peds for short cases
• adapter needed d/t lack of outer tubing

Question 24

describe the circle system.

Answer 24

• most common used in US
• more components added than Mapleson
• semi closed or closed

Question 25

what are the components of the circle system?

Answer 25

* CO2 absorber * unidirectional limbs and valves (inspiratory and expiratory) * Y- connector - FGI - APL valve - reservoir bag

Question 26

describe the unidirectional valves.

Answer 26

- "check valves" keep flow moving forward, in one direction - forward flow pushes valve up, reverse flow closes valve - inhalation opens inspiratory valve to inhale fresh gas and exhaled gas from CO2 absorber - simultaneously, expiratory valve closes to block rebreathing before it goes to CO2 absorber) * keeps inhaled and exhaled separate

Question 27

what happens with valve incompetency?

Answer 27

- may be a warped disk like with older valves allowing air to leak out backwards - my be "stuck" in up position (can sometime tap on dome to make fall but need to check if due to condensation) * condensation over time makes valve "sticky" and needs changing * malfunction of either side can lead to CO2 rebreathing and hypercapnia

Question 28

what might you see with valve incompetency during a case?

Answer 28

- end tidal CO2 waveform, during inhalation when the waveform drops, it will not drop all the way to 0 * should not rebreathe more than 2-3 mmHg CO2, if high around 9-10 definitely rebreathing CO2

Question 29

what is the best circle system set up?

Answer 29

- valves near the patient preventing backflow when circuit leaks - FGI b/w absorber and inspiratory valve (less wasted FG) - APL b/w absorber and expiratory valve conserving absorbent and less venting of FG - Reservoir bag in expiratory limb decreasing resistance to exhalation and conserves absorbent

Question 30

what are the characteristics of circle systems?

Answer 30

- allows for rebreathing of all gases with CO2 elimination - with absorber, CO2 rebreathing is prevented even at low flows (<1 L) - with low flows, gradient increases b/w delivered and inspired * increased flow leads to faster change in inspired concentration * high flows are good for induction, emergence, compensating for leaks

Question 31

what is dead space?

Answer 31

tidal volume that does not move into alveoli * found distal to Y piece (ETT); due to valves, ends where inspiratory and expiratory flows divide * breathing tube length does not affect dead space but does affect circuit compliance

Question 32

what increases resistance in the circle system?

Answer 32

-valves and absorber (but still even neonates do well)

Question 33

what controls contamination in the circle system?

Answer 33

bacterial filters often used to prevent patient cross-contamination

Question 34

what affects heat and humidity in the circle system?

Answer 34

- medical gas is dehumidified - exhaled gas is saturated at body temp * low flows with circles keep humidity in the circuit * absorbent adds heat and humidity

Question 35

what are the disadvantages of the circle system?

Answer 35

- less portable - increased risk of malfunction - problems with absorber - less predictability with low flows

Question 36

know and label the flow through the circle system.

Answer 36

1) FG enters from the CGO of anesthesia machine 2) flows through the inspiratory limb one way valve 3) flows through inspiratory breathing tube 4) through the Y-piece to the patient 5) from the patient through the expiratory breathing tube 6) through the expiratory limb one way valve 7) in and out of the reservoir bag (excess gas is vented out through APL to scavenging 8) through the absorbent canister to remove CO2 9) then back towards the patient