Breathing Circuits

Question 1

What is the breathing circuit?

Answer 1

A conduit through which gas flows at various pressures into which a specific concentration of anesthesia gases are dispensed

Question 2

What does a breathing circuit include?

Answer 2

Delivery of gas from machine to patient, removal of CO2, alteration in temp and humidity, convert continuous flow from machine to intermittent flow to and from patient, allows spontaneous/controlled/assisted ventilation, allows for gas sampling, airway pressure, flow & volume monitoring

Question 3

Resistance & Compliance of breathing circuit

Answer 3

Resistance is a measure of the pressure drop between the inlet and outlet as gas passes through a tube, compliance is the ratio of change in volume:change in pressure

Question 4

Laminar vs Turbulent flow

Answer 4

Laminar: smooth, orderly, parallel, fastest in middle Turbulent: non-parallel, eddies, same rate throughout, harder for patient to breath (can be generalized throughout tube or localized to curves/bends)

Question 5

FGF & Rebreathing

Answer 5

Varies inversely.. If FGF > minute ventilation there is NO rebreathing as long as there is a scavenging system in place (so if FGF is set at 10 LPM and mve is 10 RR & 500 TV which = 5 LPM.. no rebreathing)

Question 6

Dead Space

Answer 6

Typically about 1-3 mL/kg or about 1/3 of TV- mechanical dead space is the volume in a breathing system occupied by gases that are rebreathed without any change in composition

Question 7

American Society for Testing of Materials & APL valves

Answer 7

requires that clockwise motion increases the limiting pressure (righty tighty)

Question 8

Mapleson Breathing system does not have

Answer 8

No CO2 absorption (must use FGF to wash out CO2), no unidirectional valves, no clear separation of inspired/expired gases so will have rebreathing, easy for travel

Question 9

Mapleson E

Answer 9

Has T-piece, no bag, FGF near patient, no APL

Question 10

Mapleson F

Answer 10

Modified D- “Jackson-Rees” used for peds a lot, FGF near patient, APL @ back

Question 11

Mapleson A

Answer 11

FGF & bag at back, corrugated tubing, then APL near patient

Question 12

Mapleson B

Answer 12

Bag at back, corrugated tubing, then FGF & APL near patient

Question 13

Mapleson C

Answer 13

No corrugated tubing- bag, FGF, APL, patient

Question 14

Mapleson D

Answer 14

APL, Bag, Manometer in back, corrugated tubing to patient with FGF inlet inside and exhalation going outside around FGF inlet

Question 15

Mapleson system advantages

Answer 15

Simple, rugged, variations in minute ventilation have less effect on CO2, low resistance, lightweight, easy, lower compression and compliance volume, no CO2 absorbent problems

Question 16

Disadvantages of Mapleson

Answer 16

Need high FGF - cold and wasteful, difficult to determine ideal FGF, APL akward, can’t be used with possible MH patient

Question 17

CO2 Absorption general

Answer 17

Granule size is 4-8 mesh, channeling reduces efficiency, increased moisture improves absorption, is an exothermic reaction, may form CO if left on too long

Question 18

How to prevent CO formation

Answer 18

FGF & vaporizer off, change absorbent, no alkalis, use different O2 for nasal cannula, keep absorbent temps lower