Thanks to my posts on social media about 3D printing solutions for COVID-19 applications, I’ve been contacted by quite a few well-meaning people who are seeking help to build low cost ventilators. This has led me to spend some time studying a bunch of open-source ventilator designs involving something known as an ambu bag. The process is called manual resuscitation and involves someone manually pumping the ambu bag to force air into the lungs of a patient who is in distress and can’t breathe on their own. The important thing to note is that this is a temporary solution to be used in an ambulance or a hospital waiting room until the patient can be brought into the Intensive Care Unit (ICU) of a hospital and put on a proper ventilator. When put on a ventilator the patient will probably stay on it for days or even weeks. From what I understand, keeping a patient on an ambu bag for that long is not advisable. There are many reasons for that. Here is a very nice video explain those reasons.