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Problem anesthesia? --- It's not the vaporizer!! (anesthetic machine maintenance and trouble shooting problems)
Bruce Jones, Moderator: Nanette Walker Smith, RVT, CVT

September 5, 2001


Nanette: Good evening everyone and welcome to our chat. I'd like to introduce our speaker this evening - Mr. Bruce Jones. Bruce's background comes mainly from the "Human" side of Medicine where he worked as a Registered Respiratory Therapist for a number of years in Intensive Care Units and Neonatal Nurseries. He has also taught a "Respiratory Technician Program" at a Community College and for a private school. Bruce gained anesthesia experience working as an authorized Service Technician for "Human" anesthesia machines and in sales of Critical Care and Anesthesia Equipment. Eight years ago, Bruce started his own anesthesia service company for veterinary anesthesia equipment. With his varied background, he is able to offer a different point of view than most regarding anesthesia machines, troubleshooting, etc. We hope you enjoy this chat, Bruce, take it away!

Bruce Jones: Thank you Nanette. Tonight we will take a journey around the anesthesia machine beginning with the regulators

1. Types of oxygen regulators
a. Bourdon Style -- Wrong type for anesthesia machine Does anyone know what this type of regulator looks like? GA

Nanette: Not a clue from me!
Debbie1: no idea
Jana: na

It has one gauge that shows pressure and the other reads liters per minute either 0-8 lpm (liters per minute) or 0-15 lpm. This is not the regulator to use when using an anesthesia machine. Although it is found in many clinics. Check out yours tomorrow

Nanette: Are the gauges next to each other?
Bruce Jones: Yes, the gauges are next to each other
Jana: Why is it a bad regulator?
Bruce Jones: The anesthesia machines are designed to work at 50 psi. The bourdon regulator is designed to deliver 0 - 15 lpm oxygen. You cannot get a 50-psi output out of the Bourdon regulator.

There are two other types of regulators that are proper they are:
b. Single Stage 50 PSI Regulator - This regulator the Single stage has only one gauge. It shows only cylinder content point of interest for you, if you take cylinder content x 3 it will tell you the total # of liters left in the cylinder (large tanks). Use 0.3 x cylinder content for smaller cylinders.
c. Multi-stage 0 - 100 adjustable Regulator - The Multi-stage adjustable regulator allows you to adjust to pressure from 0 -100 psi. Any questions regarding the oxygen high-pressure system?

Susan: Why do you never want to use the last 500 lbs from an oxygen tank?
Bruce Jones: Susan, I believe it is only a matter of changing the cylinder before you run out of oxygen. You can use the oxygen until it is empty if you desire
Thomas: We have a Stephens unit and set the line pressure at 40, is this ok?
Bruce Jones: It will certainly function; you may have a reduction in the flow rate out of your flush device. The manufacturers recommend 50 psi. However, you may notice at 50 psi that you pop off the inlet-outlet adapters on your vaporizers when using the flush device. This is a result of 50 psi being directed through the system. There are restrictors available that will eliminate this inconvenience.

1. What happens when anesthesia percentages are diluted? This area of dilution is the main point of tonight's chat. The title of " It's not the Vaporizer" means this. Most of the time that there is an anesthesia related problem, i.e. the animal wakes up or you have trouble with inductions, it is not the vaporizer. The problem is dilution. Let's take a look at this important subject:
a. Difficult gas inductions of anesthesia.
b. Animals wake up under anesthesia
2. What can cause dilution to take place? Let's hear your ideas first!

Susan: Can endotracheal tubes become clogged and affect positive pressure ventilator function so that the animal does not stay anesthetized?
Jana: you flush your system causing a dilution
Thomas: O2 level too high (should be at 200mm is at 400mm liter per min flow rate)
Jana: V/Q mismatch, dead space...tubing too big...

Great ideas .... Here is my list:
A. Oxygen Flush - Your breathing bag is near empty and someone "fills" the bag with pure oxygen using the O2 Flush control.

Bruce Jones: How should you fill the bag during anesthesia administration? GA
Jana: up your flow.
Bruce Jones: Correct, use your flow meter, not the flush device. Remember, the oxygen flush bypasses the vaporizer, it delivers pure oxygen

Bruce Jones: When should the oxygen flush control be used? GA
Jana: To give pure oxy...maybe in recovery, er arrest
Page: crashing patient?
Thomas: To lighten anesthesia level.

B. Rebreathing bag contains oxygen upon startup of vaporizer. If the rebreathing bag has oxygen in it prior to you activating the vaporizer, the initial % will be lowered by this dilution taking place in the bag.

Bruce Jones: What would be the best technique to follow to minimize this dilution from taking place? GA
Jana: Charge your lines with your flow up and your vaporizer on and your Y piece plugged
Page: by increasing the rate of anesthesia?
Christine: don't turn on your O2 until you have your vaporizer at the desired percentage
Bruce Jones: Excellent!! Here is our recommended procedure to follow:

1. Empty the bag
2. Turn to vaporizer to the desired percentage
3. Turn the flow meter on
4. Fill the bag to desired level
5. Begin your induction

C. Absorber leak -- Most commonly takes place after Baralyme/Soda Sorb has been changed. What test should you perform to insure that you have an airtight circuit? I had a Vet hospital contact me last week. They were having trouble with inductions. I thought it was the vaporizer, found out their problem began at same time as their last Baralyme change; it's a common problem.

Jana: Leak test your lines. Check for leaks around your gaskets? Baralyme crystals in between gaskets
Christine: Pressure test your system before you start your patient on induction. Just a thought... always gives you a chance to make sure someone else didn't leave the pop off in the closed position also (trust no one ;)
Thomas: Plug y piece, close bypass squeeze bag
Bruce Jones: Perform a leak test, by pressurizing the system to 30 cm h2o and check for leaks. Does everyone know how to do this? We will give you info in just a few minutes regarding how to perform the test.

D. Matrix Inspiratory relief valve when rebreathing bag is near empty. If you are using a Matrix anesthesia machine with this device found on the inspiratory dome, this is a potential problem.
What is the purpose of the Inspiratory relief valve? The purpose of this valve is to allow the animal to draw in room air if the bag is empty. The problem is it allows for dilution.

E Endotracheal tube cuff herniation or too small tube utilized. The most common problem is found when the "red Rubber" Rusch tubes are utilized.
What is the difference in a High pressure, low volume cuff found on the Red tubes and the Low pressure, high volume cuff found on the Clear tubes? The red tubes put a tremendous amt of pressure against the tracheal wall, upwards of 180 mmHg. Oxygen is cut off at the tracheal wall at 30 mmHg. The red tubes should only be used for short periods of time. The cuff is subject to herniation to one side or the other thus an animal can breath around the tube

Jana: so necrosis of trachea, due to cut off blood supply
Bruce Jones: Jana, the red tubes are no longer used in human hospitals due to necrosis taking place and tracheal esophageal fistulas
Nanette: Clear tubes are easier to check if clean too!
Christine: I have seen tracheal tubes manufactured with silicone that seems to be bulbous this the same sort of problem? (i.e. the cuff doesn't inflate evenly circumferentially; bulge out on one side instead of uniformly around the tube). I understand that the cuffs on the Rusch tubes are made of polypropylene
Bruce Jones: Christine, yes this can lead to dilution of the anesthesia if the cuff is not equal on both sides.
Diana: Is there any reason why you should use the red tubes with animals? Any advantage?
Bruce Jones: None that I am aware of, they actually cost more $$
Christine: Why not use the red tubes because they are softer and meld to the shape of the trachea better because of body heat? Bruce Jones: Christine, I don't know as if that is true
Thomas: How important is length of tube?
Nanette: Very. Too long and you may go past the bifurcation too short and you may not have a good sitting behind the vocal cords
Page: and end up only in one lung!

How can you check for leaks around the cuffs during use? You should do this before use. The size of the tube is important. It must allow for a good seal to take place.

Jana: Bag your animal and listen for leaks.

So, now that you know what might be the causing the dilution, how do you trouble shoot for them? Here are some thoughts for you to consider
1. Is it the Vaporizer? Although the majority of the time it is not a problem with the vaporizer, we can eliminate it by determining if the problem happens during both non-rebreathing and rebreathing circuit application. If the problem only happens during rebreathing circuit (absorber) application, we can generally assume it is not the vaporizer.
2. If it is determined that the vaporizer is not the cause, then we must look at the following:
a. The absorber leak test must be performed. Here is the technique to employ: Turn the pop-off valve to the fully off position, place your thumb over the end of the breathing circuit (where the ET Tube would be placed), fill the bag utilizing the flush valve until the pressure gauge reads 30 cm H20. Observe for a drop in pressure. If a drop in pressure is evident, turn the flow meter on until the pressure drop stops. This will tell you the amount of leak present.
b. Look for the obvious leak: Torn bag, cracks in breathing circuit, etc. If unable to visually locate, take a soapy solution and spray it on all the absorber components. Look for any bubbling to take place. If bubbles present, you have located the leak.

Debbie2: Would Baralyme crystals present in the bag be a sign of leakage? I had this happen after new tech changed the crystals
Bruce Jones: I would not think it would be a result of leakage. You can email me particulars and we can discuss this further

c. Now correct the leak. Generally, it only takes a tightening of the absorber or a replacement of a part.
d. Still can't figure it out.... Call a professional... Call me!!

SCAVENGERS: What type of scavenger system do you have?

Michelle: F-Air System
Thomas: F-Air
Jana: been trying to get on going for 2 years...grrr. F-air in SA not much in LA Types of

Scavenger Systems include the following:
1. F-Air Canisters -- How often should these be changed? GA

Jana: F-air...100hours??
Michelle: When they gain 50 grams in weight?
Thomas: We go by Weight
Bruce Jones: would you believe every 12 hours of operation?
Jana: ... thud...
Debbie2: oh my.
Thomas: been breathing lot of isoflurane then
Bruce Jones: Per the manufacturer
Thomas: Does the weight gain in the canisters mean anything?
Bruce Jones: I have heard about using the weighing technique from techs but have not seen anything from the manufacturer

2. Passive Systems --- What concerns do you have with this style? If you do have a passive system, make sure that each inlet has its own outlet... not connected room to room.

Nanette: Passive.... no active removal of it just sits in the tube till it goes out the window or whatever.

3. Active Systems - An important part of an active system are the Interface valves -- what is an interface valve? Many active systems do not have interface valves. These valves prevent the active system from drawing gas from the absorber/ patient system.
Do you have an active system w/o an interface mechanism?

Nanette: don't know...will have to look!
Bruce Jones: If you don't e-mail me!

Why is it important to have an effective scavenger in place? GA

Michelle: Protect staff from harmful effects of waste gases
Page: minimizes exposure to waste gas
Bruce Jones: Scavengers are often a neglected area in the hospitals I service. Do your best to make sure that this is an important function in your hospital!!
Jana: Would fair work on my LA machine with high ventilation pressures and how important is yearly recalibration
Bruce Jones: Jana, e-mail later. We can discuss details
Bruce Jones: Since most of you are using Fair canisters you need to be aware that they can build up resistance to the exhaled gas. This will cause an increase in positive pressure to show on your pressure manometer and your breathing bag to enlarge. Also, make sure that the bottom of the fair is patent, not sitting on top of something.

Let's wrap up our chat for the night with a question and answer session? I will try to answer any questions that you may have regarding the subjects we have discussed or regarding any anesthesia machine questions that you may have. Questions? GA

Diana: I don't know much about anesthesia machines yet but we have a system with granulate which turns from white to blue when getting old what's that please?
Bruce Jones: The Baralyme changes color as a result of use. It needs to be changed when it becomes discolored. My experience has been that the Baralyme needs to be changed more often than it generally is in an hospital.
Thomas: What is your opinion of the Stephens machine? We like it
Bruce Jones: My experience has been that the Vets either love them or hate them. I service all types of machines. The Stephens machine is a difficult machine to change the Baralyme, as you probably already know. Also, the Baralyme cannot be seen in the Stephens machine, so change it often
Diana: Can you recommend a book to get basic info about anesthesia machines?
Bruce Jones: Diana, e-mail me, I will give this some thought.

When you have a question regarding Anesthesia Machine Problems, who you gonna call??? Please feel free to email me, Bruce Jones at FM@LVCM.COM or contact me at 1-888-378-8071. It's a toll free call and I am happy to assist you at any time. Also, visit our website at for your equipment and supplies for anesthesia, dental, monitoring, and more. Thank you for your time and interest. Hope you enjoyed the session

Thomas: Enjoyed it thanks
Dawn: thanks Bruce!
Diana: was fun,bye
Debbie2: thank you Bruce and Nanette. I will be reviewing hosp practices tomorrow.
Michelle: Very informative, thanks
Jana: thanks....!!
Page: thanks, much
Elizabeth: thanks
Dawn: My dog is grumbling at me .. must be dinner time! g'night! :)
Diana:thanks for book info
Jana: - that will give you the anesthesia machine, but it has lectures on's sooo great!!

Participants: Nanette, Christine, Danielle, Dawn, Debbie1, Debbie2, Diana, Elizabeth, Jana, Page, Phyllis, Susan, Thomas

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