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      Hear from Our Experts: Tips on Checking Your Anesthesia Equipment


      Today, three of our queen anesthesia bees🐝, all of whom are Certified Veterinary Technicians, are sharing detailed guides on how to perform common procedures for checking and troubleshooting your anesthesia equipment.


      1: Pressure Testing the Versa II



      My name is Tia Piering, and I have been a certified veterinary technician for 19 years. I have been with Patterson almost 8 years and in my current role for 3 years. Today, I am going to show you how to perform a pressure test on an anesthesia machine as well as go over a few other tips to verify your anesthesia machine is working properly.

      It is very important to pressure test any anesthesia machine upon initial setup as well as continue to do so daily. The main reason for this is patient and staff safety. If there is something disconnected, or not attached properly that causes a leak, you can expose your staff to waste anesthetic gas as well as compromise the safety of the patient. Depending on the location of the leak, the anesthetic gas may never reach the patient so after their premedication and induction agent wears off, the patient can wake up. Another issue is that if they are not getting anesthetic gas they are also not receiving oxygen from the machine, which may cause serious effects such as hypoxia. In this video, I will be pressure testing the Patterson Versa II anesthesia machine, but the same steps apply to other brands of anesthesia machines as well.



      Test Procedure

        1. Connect the Versa II to an appropriate oxygen source regulated between 50 and 60 psi.
        2. Make sure that the flowmeter is OFF and the ball does not indicate any flow.
        3. Connect the F-circuit and breathing bag to the Versa II.
        4. Make sure the switch on the Versa II is set to “Rebreathing” (this step applies specifically to the Versa II).
        5. Close the pop-off valve.
        6. Occlude the end of the F-circuit at the elbow connection with your thumb.
        7. Pressurize the absorber system using the flush valve until the manometer reads 30 to 40 cmH2O.
        8. After the pressure stabilizes, observe the needle on the manometer. The needle should not drop more than 5 increments in 20 seconds. If the pressure drops rapidly or the bag deflates, a leak is present and needs to be corrected.


      When finished with the pressure test or back pressure test, please be sure to completely open the pop-off valve first, then release your thumb from the end of the f-circuit.  It is very important to do this in the correct order so that the pressure is not released through the end of the breathing circuit which can allow sodasorb to enter the inhalation/exhalation valves and breathing circuit.


      Places to check for leaks:

          1. Inhalation/exhalation valves (dome caps)
          2. Around the absorber canister
          3. Around the pop-off valve
          4. End caps on the vaporizer
          5. Hole in the breathing bag or circuit hoses
          6. Silicone tubing or connectors

      If you are still unable to find the leak, use the following steps to locate it.

          1. Turn the flowmeter on just enough to keep constant pressure in the machine and spray soapy water to isolate the leak (bubbles will appear), paying attention to all connections and areas listed above.

      The image below shows how the soapy water is indicating where there is a leak where the absorber canister seals.

          1. It is necessary to correct leaks of 200 ml or greater, then perform another pressure test.

      Another great test to perform on a regular basis is the Back Pressure Test.


      Back Pressure Test

          1. Connect a short tube from the inhalation valve to the rebreathing bag port and close the pop-off valve (you can remove the short corrugated tube from your F-circuit and use that).
          2. Turn flowmeter up to 200 ml and observe the manometer/pressure gauge.
            1. Result: Gauge should slowly rise past 20 cmH2O (machine passes).
            2. If it does not, inspect the flutter discs inside the inhalation and exhalation valves, clean them and/or replace them.


      If you have any other questions, please contact the complimentary Patterson Veterinary Anesthesia Hotline at 866-825-6076, M-F, 8 AM-5 PM CT.


      2: Anesthesia Flowmeter Basic Repair



      My name is Sarah Zabel. I began my veterinary technician journey in the fall of 2006 at Madison Area Technical College, enrolled in the Veterinary Technician & Laboratory Animal Technician program. I completed my education there and started working in the veterinary field in 2009; that same year I became a certified veterinary technician (CVT). I have worked in various veterinary settings and roles. In 2014 I completed the requirements, and testing, with AALAS to obtain Registered Laboratory Animal Technologist (RLATG) certification. I have been with Patterson Veterinary in my current role, Support Specialist, since July 2016.

      I will be walking you through a basic repair on your anesthesia flowmeter. I will also be discussing a “big bag” problem you may encounter, and how to determine if it is an emergency situation or a normal function.


      Needle Valve Adjustment

      Does the ball in your flowmeter not turn off when you turn the knob to the closed position? If so, a simple adjustment could fix the problem.

          • For most model flowmeters, you will need a 1/16" Allen wrench to remove the set screws from the knob.* Once the set screws are removed, pull the knob straight off.


          • Once the knob is removed, you will see the needle valve. Turn this valve clockwise until the ball rests on the bottom of the tube.


          • Place the knob back on the valve. Turn it slowly clockwise until you feel it “click” into place.
          • Place the set screws back into the knob, thread, and tighten them back into place.


          • Check the function of the flowmeter by opening and closing the knob. If the ball is still not resting on the bottom of the tube when turned off, repeat the above steps. If it seems the needle valve is stripped, the needle valve assembly will need to be replaced.


      *Some flowmeter knobs do not have set screws, and can pull straight off. Always check for set screws before pulling the knob off.


      Big Bag

      An overly inflated breathing bag can be a cause for concern. Here are a couple of things to check to rule out an emergency situation.

      Note: A complete pressure test should be performed on your anesthesia machine before use. Make sure the manometer is at 0 cmH2O when not in use.


          • Is your pop-off valve completely OPEN? The pop-off valve should be completely open when the anesthesia machine is in use.
          • Check the manometer. Is the pressure exceeding 2 cmH2O? If the pressure is rising above this mark, your pop-off valve may be either closed or malfunctioning.

      If the above items check out, evaluate the following:

          • Check the patient’s breathing pattern (i.e., shallow breathing, holding their breath).
          • Check the bag size. Is the appropriate breathing bag being used for the size of the patient?
            • Breathing bag size is determined by calculating tidal volume. Tidal volume is 10-20 ml/kg. After calculating tidal volume, multiply that by 6. The answer will be in milliliters so then you will need to convert to liters to determine the bag size.*
          • Check the O2 flow rate being used. Is the O2 flow rate being used appropriate for the patient?
            • 1-2 LPM for a rebreathing system for patients greater than 7 kg*
            • 100-120 ml/kg/min for a non-rebreathing system for patients less than 7 kg*
          • Check your waste gas removal system, and make sure it is operating efficiently.


      For passive system:

          1. Check the integrity of the waste gas tubing (confirm it is not clogged or kinked).
          2. If using a charcoal filter, check to make sure it is vented properly.
          3. If venting to the outside, check outlet for a blockage (bird’s nest, debris, etc.).


      For active system:

          1. Check the integrity of the waste gas tubing (confirm it is not clogged or kinked).
          2. Check the unit itself:
            1. Is the power on?
            2. Check vacuum/draw with manufacturer recommended device.





      If you have any other questions, please contact the complimentary Patterson Veterinary Anesthesia Hotline at 866-825-6076, M-F, 8 AM-5 PM CT.


      3: When to Change the CO2 Absorber Granules



      Hello, my name is Amanda Strayer. I have been working at Patterson Veterinary for the last 6 years. I have been a Certified Veterinary Technician for 19 years, with 13 years’ experience at a veterinary emergency and specialty facility working primarily within the surgical department.

      Performing daily maintenance to the anesthesia machine helps to ensure patient and staff safety. During anesthetic procedures, monitoring and caring for the patient is the primary focus; therefore, it’s important for the anesthesia machine to be maintained regularly to avoid equipment complications. Daily checks may include checking the oxygen tank level, waste gas system to make sure it’s functioning, refilling the vaporizer, changing bags and breathing circuits as needed and performing a pressure/leak test. Throughout the day, it’s common to check the level of anesthetic in the vaporizer and check the F/Air canister if used; however, the Sodasorb may be overlooked and not changed as frequently. As one procedure is finished, and preparation begins for the next, one should also consider checking the Sodasorb and changing it if needed to prevent hypercapnia. The physiological effects of hypercapnia are complex and wide-ranging.* Hypercapnia (increased arterial PCO2) can be related to a number of factors during anesthesia.* CO2 production to elimination can be exacerbated by increased levels of inspired CO2 as a result of exhaustion of the soda lime.* There are several indicators of Sodasorb exhaustion and many are familiar with the color change.

      The color change that occurs to Sodasorb is a pH reaction which occurs when moisture from the expired breath contacts the granules. Ethyl violet color dye (a sensitive acid-base indicator) is added during the manufacture process.* Deactivation of the dye can occur from exposure to light and especially when the granules are dry. Some factors that affect moisture of the granules or which cause evaporation of moisture to the granules are as follows:

          • Excessive use of the O2 flush button.
          • Granules that have been left in an opened and unsealed container.
          • Sodasorb left in the absorber canister of the anesthesia machine. Note: the manufacturer of Sodasorb recommends changing the granules in the anesthesia machine if the machine has not been used in 48 hours.



      Do you recall a time when the Sodasorb granules changed purple, then after use, the granules changed back to white? As the granules sit unused, the lack of moisture stops the purple color (pH) change process and a different chemical process takes over, turning the granules back to white. Therefore, the granules could be nearly or completely exhausted, yet appear white (good for use). Using a combination of indicators will help you decide if it’s time to change the Sodasorb granules.


      Indicators for loss of Sodasorb activity:

          • Use the capnograph on your anesthesia monitor.
          • An elevated iCO2 (inspired CO2) reading can be an indication of expired Sodasorb granules.
          • During inspiration the base line does not return to zero.
          • Elevated ETCO2 readings.


      A normal ETCO2 Waveform

      An abnormal Waveform where the baseline is not returning to zero


          • Replace the granules every 8-12 hours of use or when the Sodasorb has been sitting unused in the anesthesia machine for 48 hours or more.
          • Lack of heat production during use. However, heat does not affect the ability of the granules to absorb CO2. It’s more of an indicator that the chemical process, absorption of CO2, is taking place. Some of the variables affecting heat generation are the patient’s rate of carbon dioxide production, body size, metabolic rate, body temperature, and the ambient air temperature in the operating room (Sodasorb Manual of CO2 Absorption).*
          • Hard granules. Fresh soda lime granules feel soft and crumble when rubbed between thumb and fingers.
          • Replenish the absorbent when one-third to one-half of the granules undergo a color change. On average this will be every 8-12 hours of use; however, it can become exhausted more quickly. Therefore, color change should not be the only indicator relied upon. To help monitor the number of hours the Sodasorb has been in use, Sodasorb canister labels are available through Patterson Veterinary. The label stays adhered to the canister, yet is easily removable when it is time to change the absorbent and replace with a new label.



      Patterson item number 78938052 label CO2 absorbent usage

          • When using the color indicator method, turning blue/purple during use, make sure you know what brand of absorbent is being used. The brand name Sodasorb LF changes to light purple/lavender immediately upon first use and will turn a darker shade of purple as it becomes exhausted.
          • A color indicator for Sodasorb LF can be ordered and used as reference to help determine when Sodasorb LF is exhausted (Patterson item # 78604599).


      There is no magic number of hours or a set day on the calendar when Sodasorb granules should be replaced. Color change should also not be the sole indicator on when the granules have become exhausted or desiccated (dried out). The best way to determine when it’s time to change Sodasorb granules is by using a combination of indicators.


      For complete details regarding Sodasorb, refer to the manufacturer of the product being used.



      *Sodasorb Manual of CO2 Absorption. Cambridge, MA: W.R. Grace & Co.-Conn., 1993.


      If you have any other questions, please contact the complimentary Patterson Veterinary Anesthesia Hotline at 866-825-6076, M-F, 8 AM-5 PM CT.