Bag Sizing

13 April 2020

This page details various bag sizes and why the bag supports in any design should be adjustable. The key is to find points on each bag that provide support and lateral constraint, but do allow the bag to flex as it is compressed. The bag should be centered laterally and vertically between the grippers. The table below gives dimensions at the contact points and the center of the bag. We place the bag with the bottom towards the motor and head, with patient valving, overhanging. Remember, this valving must be extended as described in Plumbing.

For practical purposes, spacing the bag mounts 21 cm apart should fit most bags, but the mounts must have vertical adjustability.

bagdistancebottom øtop øcenter ø
Ambu Spur II
& Adult Silicon
Care Fusion2154.550134
Laerdal The Bag21na40139

Below are pictures of each bag type that we measured, shown in Version 2:
Note: In Version 3 we added hooks and an elastic to prevent unintended bag removal.

Ambu brand bag, note use of barb fitting to secure rear of bag

Using a phone level to position a Care Fusion bag
The Laerdal bag is large. Care must be taken to not pinch the bag when compressed and, as seen here, the bag lifts up and out in current configuration. This is not a good fit and longer arms are needed.
The Portex bag is cool because it comes in purple, but it is hard to secure properly.

32 Replies to “Bag Sizing”

  1. Jim Sullivan
    Jim Sullivan

    Also, any consideration to using thin quick release fasteners, such as velcro straps, on the plexiglass ends to secure the bag so it wouldn’t be accidentally moved or dislodged? It might also solve the Portex bag problem, and the bag could still be quickly removed for manual use in case of an error or malfunction.

      • NYMC Team
        NYMC Team

        Tidal Volume (TV) = inspiratory flow x inspiratory time
        Minute ventilation = VE = (TV x respiratory rate)
        TV = minute ventilation / respiratory rate

        Tidal volume is a set parameter in volume controlled ventilation. The tidal volume that is set by the clinician may be determined through the consideration of multiple factors, such as the patient’s body weight, physiologic state of the patient, plateau pressure, desired minute volume, etc. More information can be found under the “clinical” page of the website (link:

  2. Diego Rodriguez
    Diego Rodriguez

    Good morning team, You had mentioned US Air Project printing the valve manifold for use, do you by chance have the file? Did they make you one? We have a team of engineers working through the production of these units and outside all the information readily available, this is one piece of puzzle we are hoping to not recreate. So far we have PCB design done, materials en route, and CNC/3D Printing resources lined out. Excited to start building.

  3. bhavesh bhatt
    bhavesh bhatt

    There is always a chance that “Ambu” bags and such will be in short supply also, various labs are using same bags with different ways to compress it, why not use a bellows based machine, where the bellows can be made locally by locally made materials (leather, vinyl, rubber etc).

  4. Art Jensen
    Art Jensen

    I have access to a large tier 1 supplier of injection molded parts and metal stamping. The owner and CEO is willing to have his mold shop and his plastics company make anything necessary. He is not looking for startup money or profits. He would like to see a device sold for under $1000.00 dollars and that is not a typo. They can produce thousands of parts daily. He has had the best 4 years of his companies history and wants to give back to America.

  5. Kathiresan Sundarappan
    Kathiresan Sundarappan

    In India, a group of doctors are against using this design of ventilator with bag. They can be convinced if it has been deployed somewhere in US or other countries.Can you please let us know what is the current status of testing, certification and deployment at Cambridge or other locations?

  6. Farrukh Nagi
    Farrukh Nagi

    Present system is bi-directional system and motor need to be reversed for inspiration and expiration cycle. Reversing motor for days is not good for motor controller and will have reliability issue. Why can’t one direction motor operation can be used with cranking wheel or Cam?

  7. Lok WM
    Lok WM

    From download 3D model, the bag holder distance is around 300mm. And the bag distance is 210mm. Do I have misunderstanding for the dimension? Does anyone have a detail dim spec for the bag? I am going to design the bag holder, wish someone can help me to get the about dim spec. Thanks!

    • NYMC Team
      NYMC Team

      Please refer to the “Bench Testing” page on the E-Vent website (link: Here you will find the results of durability testing trials where the E-Vent was tested for 24 hours with no securement other than being placed in the mounts in order to determine it would move. After the 24 hour test, the bag had not changed position, indicating it experienced no torque that would cause it to move during operation. More detailed information regarding this test and the other tests that were performed can be found on the “Bench Testing” page. Also, as you can see in the picture of E-Vent Version 3 on the homepage, we used an elastic band to hold the manual resuscitator in place.

    • NYMC Team
      NYMC Team

      This will likely vary based on the patient’s health status and subsequently the machine settings. Because this is a volume control machine, the applied pressure is varying. Therefore, different pressure requirements implemented on the Ambu bag will affect the longevity of the bag. For example, higher pressures will be required for an obese patient compared to one with a normal BMI.

      Additionally, this machine allows for different bag sizes and brands, which will demonstrate variations in Ambu lifespan. Since this machine utilizes the bags in a different manner than its on-label use, previous data examining the Ambu bag longevity is not entirely applicable in this situation. Patients with acute respiratory distress, like COVID-19 patients, have lower compliance lungs compared to the average person. Therefore, higher pressure may be required within the bag to deliver a desired tidal volume. The longevity of the bags may be different than their longevity observed in other emergency situations, like cardiopulmonary arrest.

      Bench testing done used the Ambu Spur II. The bag was in good condition after a 24 hour wear test. However, there were shortcomings to this test, as the bag did not experience the resistance that would occur when delivering oxygen to a low compliance lung, as in ARDS. Also, because this is a disposable bag, the longevity is likely less than one used in a hospital setting, like the Ambu Oval Silicone Resuscitator. One technique that could also increase the lifespan of the bag is to rotate it periodically in order to more evenly distribute the stresses. Additional information can be found on the “Bench Testing” page (Link: regarding the various testing and troubleshooting performed with the Ambu bag.

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