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

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

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

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

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

And you are…

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

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

Don’t obsess on naming each part

Just grab the big picture

The Gas Machine

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

… at the common gas outlet

Find the Common Gas Outlet

Let’s look at the gas machine…

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

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

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.

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

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

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

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.

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.

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.

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)

(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.

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.

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!

How much gas should I use?

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?

Comfort zone – you have a feel for it…

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

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

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

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.

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%

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”?

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.

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

The trouble with WAG

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

The trouble with WAG Most scavenging systems vent to the atmosphere

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. 2011 Oct-Dec; 27(4): 435–437

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

The trouble with WAG …brand new machine …charcoal absorber

Lower gas flow helps reduce WAG

This presentation is provided with support from: For a copy of this slide deck email Ken Crump kcrump@darvallvet.com