1. Anesthetic Gas Machines
How do these things work anyway?
Ken Crump, AAS, AHT
Director of Operations, DarvallVet,

2. DarvallVet a division of Advanced Anesthesia Specialists
Founded in 1996
Global innovator
Sydney, AU (home)
Hong Kong
United Kingdom
Dubai
North America
Owned / Operated by Colin Dunlop, DVM, DACVAA
We design, manufacture, distribute Darvall brand anesthesia products
World’s first heated breathing circuit
We provide
Anesthesia / Patient Warming equip
Technical services
Expertise
Continuing education

3. Who is this Ken Crump guy?
Graduate of BelRea Institute of Animal Technology, Denver
Let’s just say “last century”
25 years with CSU Veterinary Teaching Hospital
Research – radiation therapy
Anesthesia – clinical instructor
Oncology – Animal Cancer Center
Complementary / Alternative Medicine – acupuncture, homeopathy, flower essences
Anesthesia faculty: Vet Tech Program, FRCC
Director of Operations, DarvallVet –
a division of Advanced Anesthesia Specialists
Author, silversmith, fly fisherman, grandpa

4. The point of the exercise…
Anesthesia is
Important
Part science / Part art
Terrifying
If you can’t explain it simply, you don’t understand it well enough – Albert Einstein

5. A good surgeon deserves a good anesthetist
A bad surgeon needs one

6. And you are…

7. When you know how something works You tend to make better use of it
At first:
And then:
You do what you were taught
Patients go to sleep
Patients wake up
You gain confidence
You begin to learn more
You administer anesthetic gas more precisely
Your patients stay warmer
You reduce workplace contamination
You reduce environmental pollution
You reduce the cost of doing gas anesthesia

8. All gas machines work the same way
Whether they look like this…
Or this…

9. Don’t obsess on naming each part

10. Just grab the big picture

11. The Gas Machine

12. Here is where the breathing circuit ends and the gas machine begins…

13. … at the common gas outlet

14. Find the Common Gas Outlet

15. Let’s look at the gas machine…

16. Follow the flow of oxygen
The oxygen source
Tank, generator or house system
To calculate the estimated remaining tank volume, follow this example:
An E-cylinder contains 660 L, and has a full-pressure of 2,200 psi.
Pressure drop is proportional to remaining O2 volume.
(0.3 X psi) = #L in tank
A tank with 500 psi has 150 L.
When used at a flow rate 1 L/min, it will last approximately 2 ½ hr.
1 L = 1 minute
150 L = 150 minutes
150 minutes = 2 ½ hr

17. Follow the flow of oxygen
The oxygen source
The pressure reducer
Reduces the pressure from the oxygen source to a constant pressure at which the machine is designed to operate – usually around 50 psi

18. Follow the flow of oxygen
The oxygen source
The pressure reducer
Flow Meter
Converts oxygen pressure to oxygen flow, and controls the rate of oxygen flow through the vaporizer. The anesthetist determines the rate of oxygen flow.

19. For more information
Read Making Anesthesia Easier blog post:
“Go With The Flow – How to decide the oxygen flow rate for small animal anesthesia”
Go to DarvallVet.com and follow the link to the blog

20. Follow the flow of oxygen
The oxygen source
The pressure reducer
Flow Meter
Vaporizer
Converts liquid anesthetic to a gas and mixes it with oxygen as a precise percentage of total flow

21. A quick word about vaporizers What is a precision vaporizer?
Non-precision
Precision

22. A quick word about vaporizers
What is a precision vaporizer?
Uses oxygen flow from the flow meter to volatilize a liquid.
Splits the oxygen stream through a variable bypass.
The main stream passes directly through the vaporizer to the outlet
The dial setting controls the second stream, which passes through the vaporizer sump to become saturated with the volatile liquid.
Second stream combines with the first stream to deliver the % of anesthetic gas indicated on the dial.

23. A quick word about vaporizers
Vaporizers haven’t changed significantly in 50 years.
The vaporizer you’re using on that 8# Yorkie was designed to anesthetize a 150# human
Your vaporizer is calibrated at 5L/min, and you use much lower flow rates in veterinary anesthesia
Your vaporizer needs to be serviced annually
Even freshly cleaned and calibrated, your vaporizer leaks gas into the room.

24. A quick word about vaporizers
What if you tip it beyond 45o?
Drain it
Take the machine away from people
Open vaporizer up to 5%
Run 4 liters O2 flow through the vaporizer for 45 minutes to an hour
Put it back in service.

25. Follow the flow of oxygen
The oxygen source
The pressure reducer
Flow Meter
Vaporizer
Flush valve
Bypasses the flowmeter and the vaporizer, and flushes the system with a large volume of oxygen (50 – 75 liters per min)

26. (50 – 75 liters per min)
The oxygen flowrate for a non-rebreathing circuit is usually ~200ml/kg/min
Do Not use the flush valve when you are using a non-rebreathing circuit.

27. Follow the flow of oxygen
The oxygen source
The pressure reducer
Flow Meter
Vaporizer
Flush valve
Common gas outlet
Often called the fresh gas outlet
The point at which combined gases leave the gas machine and go to the breathing circuit.

28. Follow the flow of oxygen
The oxygen source
The pressure reducer
Flow Meter
Vaporizer
Flush valve
Common gas outlet
That’s all there is to it!

29. How much gas should I use?

30. How much gas should I use?
The short answer:
Only use as much anesthetic gas as the patient needs at any given time during the procedure.
Sometimes the short answer is not enough information
Where do you start?

31. Comfort zone – you have a feel for it…

32. Let’s look at a brand new gas
What do you need to know about it before you’re ready to use it?

33. MAC
“Minimum Alveolar Concentration (M.A.C.) required to prevent purposeful movement from a noxious stimulus”
It’s how we determine relative potency of different anesthetic gases

34. MAC
“Minimum Alveolar Concentration (M.A.C.) required to prevent purposeful movement from a noxious stimulus”
It’s how we determine relative potency of different anesthetic gases

35. MAC
If 1 X MAC is sufficient to prevent purposeful movement from a noxious stimulus, what factor of MAC is required for surgery?
1.25 – 1.5 X MAC for surgery.

36. MAC
What affects a patient’s requirement for the MAC of anesthetic gas?
Physical Status
Pre-meds / analgesics
The degree of surgical stimulus
The “other” 50%

37. How much gas should I use?
The MAC of “C3PO” is 9%
The MAC of isoflurane is ~1.4%
The MAC of sevoflurane is ~2.1%
Which drug is most potent?
Where would you guess your vaporizer dial setting would be during surgery if you were using “C3PO”?

38. How much gas should I use?
The MAC of “C3PO” is 9%
The MAC of isoflurane is ~1.4%
The MAC of sevoflurane is ~2.1%
If 1 X MAC is sufficient to prevent purposeful movement from a noxious stimulus, what factor of MAC is required for surgery?
1.25 – 1.5 X MAC for surgery.

39. How much gas should I use?
The MAC of “C3PO” is 9%
The MAC of isoflurane is ~1.4%
The MAC of sevoflurane is ~2.1%
Where would you guess your vaporizer dial setting would be during surgery if you were using “C3PO”?
1.25 to 1.5 X MAC for surgery.
1.25 to 1.5 X 9%(MAC)= 11.25% to 13.5% C3PO for surgery

40. The trouble with WAG

41. The trouble with WAG
All waste anesthetic gases (WAG) have significant ozone-depleting potential.

42. The trouble with WAG
Most scavenging systems vent to the atmosphere

43. The trouble with WAG
Assuming about 200 million anesthetic procedures are performed annually world wide, it is estimated that the global emissions of inhaled anesthetics are equivalent to 9.5 million tons of carbon dioxide.
J Anaesthesiol Clin Pharmacol Oct-Dec; 27(4): 435–437

44. The trouble with WAG
That is equivalent to the emissions from 1,000,000 cars

45. The trouble with WAG
…brand new machine
…charcoal absorber

46. Lower gas flow helps reduce WAG

47. This presentation is provided with support from:
For a copy of this slide deck Ken Crump