What are the different colours of the gas cylinders and the gases in them?
White = O2
Blue = N2O
Grey = CO2
Brown = He
Black & white = Air
White & brown = He & O2
White & blue = N2O & O2
What is the equation for Boyle’s law? When is it used?
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
What is the gas pressure in all pipelines except surgical air?
4
Surgical air: 7
How does a bourdon gauge work?
Like party blower - inc pressure tube straightens, lower pressure will curl up measured against atmospheric pressure
How much CO2 is absorbed by 1kg of soda lime?
250L
What is the reaction in soda lime?
H2O + CO2 -> H2CO3
H2CO3 + 2NaOH -> Na2CO3 + 2H2O + heat
Na2CO3 + Ca(OH)2 -> CaCO3 + 2NaOH
How does a vaporiser work?
- 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
What is saturated vapour pressure?
Pressure exerted by a vapour in equilibrium with its liquid at a given temperature
What does a high SVP mean?
More volatile
Why does Desflurane have it’s own type of vaporiser?
- ## Boiling point 23.5 so large swings in SVP
What affects SVP?
Temp
what are problems with vaporisers?
- Flow rate dependence
- Overfilling (volatile spills into bypass chamber)
- Pumping effect (inc output conc)
- Pressuring effect
What are the different types of breathing systems?
- 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
What are the advantages of a circle system?
- Heat/moisture conservation
- Scavenging
- Reduced cost
- Small dead space
- Good for long cases
- Low-flow anaesthesia
What are the disadvantages of a circle circuit?
- 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
What does a CO-Oximeter measure?
Measures fractional O2 saturation of following:
- Oxy Hb
- DeOxygenated Hb
- CO Hb
- Met Hb
SaO2
What is the Beer-Lambert Law?
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
What are key points of in vitro Oximetry?
- 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
What are the 2 types of pulse oximeters?
- Transmission
- Reflectance
What is the difference between CO-Oximetry & pulse Oximetry?
CO: Fixed path length = absolute absorption, multiple wavelengths used
Pulse: Variable path length = 2 wavelengths and ratio of absorption used
What is the Isobestic point?
- Point on absorption graph where Oxy & Deoxy Hb absorbed equally (805)
- Can be used to determine Hb conc
Why does CO Hb Overdose show normal O2 sats?
Same absorption point as Oxy Hb on absorption graph
How does the SaO2 % relate to the wavelengths?
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
