Equipment and breathing systems

Question 1

What are the different colours of the gas cylinders and the gases in them?

Answer 1

White = O2
Blue = N2O
Grey = CO2
Brown = He
Black & white = Air
White & brown = He & O2
White & blue = N2O & O2

Question 2

What is the equation for Boyle’s law? When is it used?

Answer 2

P1 x V1 = P2 x V2

(p1 = gauge pressure, v1 = physical volume, p2 = atmosphere pressure. v2 = actual amount of gas in cylinder)
Used to measure amount left in a gas cylinder

Question 3

What is the gas pressure in all pipelines except surgical air?

Answer 3

4
Surgical air: 7

Question 4

How does a bourdon gauge work?

Answer 4

Like party blower - inc pressure tube straightens, lower pressure will curl up measured against atmospheric pressure

Question 5

How much CO2 is absorbed by 1kg of soda lime?

Answer 5

250L

Question 6

What is the reaction in soda lime?

Answer 6

H2O + CO2 -> H2CO3
H2CO3 + 2NaOH -> Na2CO3 + 2H2O + heat
Na2CO3 + Ca(OH)2 -> CaCO3 + 2NaOH

Question 7

How does a vaporiser work?

Answer 7

• Gas passes through vaporises under pressure splits into 2 streams
  1) 20% passes via vaporising chamber - gas leaving is fully saturated
  2) Rest enters bypass chamber
• High resistance

Question 8

What is saturated vapour pressure?

Answer 8

Pressure exerted by a vapour in equilibrium with its liquid at a given temperature

Question 9

What does a high SVP mean?

Answer 9

More volatile

Question 10

Why does Desflurane have it’s own type of vaporiser?

Answer 10

• ## Boiling point 23.5 so large swings in SVP

Question 11

What affects SVP?

Answer 11

Temp

Question 12

what are problems with vaporisers?

Answer 12

• Flow rate dependence
• Overfilling (volatile spills into bypass chamber)
• Pumping effect (inc output conc)
• Pressuring effect

Question 13

What are the different types of breathing systems?

Answer 13

• Open: Resp tract open to atmosphere
• Semi-open: Volatiles carried by FG can be diluted by RA (Venturi, Hudson mask)
• Semi-closed: Volatiles carried by FG but no RA dilution (rebreathing systems with/without CO2 absorption, NRB)
• Closed: Circle system with expiratory valve closed

Question 14

What are the advantages of a circle system?

Answer 14

• Heat/moisture conservation
• Scavenging
• Reduced cost
• Small dead space
• Good for long cases
• Low-flow anaesthesia

Question 15

What are the disadvantages of a circle circuit?

Answer 15

• Multiple connections
• Valves can stick
• Open rebreathing
• Closed = asphyxia
• Bulky
• Need for gas analyser
• Potential for infection
• CO formation on low flow with des/sevo
• Compound A with sevo

Question 16

What does a CO-Oximeter measure?

Answer 16

Measures fractional O2 saturation of following:
- Oxy Hb
- DeOxygenated Hb
- CO Hb
- Met Hb
SaO2

Question 17

What is the Beer-Lambert Law?

Answer 17

Intensity of light transmitted through a transparent substance decreases in relation to the conc of the substance and the length of the path it travels through

Question 18

What are key points of in vitro Oximetry?

Answer 18

• Fixed path length
• Sapphire glass
• Red cells disrupted
• Measures free Hb
• Multiple Wavelengths to measure all types of Hb
• Fractional Hb Conc increased
• SaO2 NOT SpO2

Question 19

What are the 2 types of pulse oximeters?

Answer 19

• Transmission
• Reflectance

Question 20

What is the difference between CO-Oximetry & pulse Oximetry?

Answer 20

CO: Fixed path length = absolute absorption, multiple wavelengths used
Pulse: Variable path length = 2 wavelengths and ratio of absorption used

Question 21

What is the Isobestic point?

Answer 21

• Point on absorption graph where Oxy & Deoxy Hb absorbed equally (805)
• Can be used to determine Hb conc

Question 22

Why does CO Hb Overdose show normal O2 sats?

Answer 22

Same absorption point as Oxy Hb on absorption graph

Question 23

How does the SaO2 % relate to the wavelengths?

Answer 23

100% = Oxy Hb, mostly 940 absorbed
85% = Seen with high levels of Met Hb as absorbed both wavelengths equally
0% = Deoxy Hb, mostly 660 absorbed