## 1 Introduction  
The international health crisis caused by the rapid propagation of the SARS-CoV2 (COVID-19) has triggered an unprecedented type of collaborative and distributed development worldwide. From professional scientists, physicians and engineers in universities, research institutions and companies to individuals with home-based electronics and mechanics building capabilities have started intensive brainstorming, prototyping, re-engineering and testing of potential solutions to multiple aspects of the pandemic.  
Taking into account the experience gained in China and Italy, two of the earliest and most affected countries by the pandemic so far, it is clear that a key piece of equipment required at hospitals are mechanical ventilators and that the number of available ventilators is insufficient with regard to the potential numbers needed in most countries worldwide [1]. On 13 March 2020, we decided to start an emergency project to develop and evaluate the potential of a platform for low-cost, easy-to-build ventilators to cope with the potential shortage of ventilators worldwide. During the following days, an interdisciplinary group was formed including people with backgrounds in physics, engineering, informatics, medicine, etc. to shape up ideas. Quickly, two approaches were chosen, prototypes started to be built, tested and optimized for performance and reliability. In this contribution, we present two ventilator prototypes of the most basic approach that are based on the use of a bag-valve manual ventilator.  
The design framework shown here is made to be a low cost design, easy modification of widespread standard components, or at least easy to manufacture and basic ventilator capacity. In addition, we enumerate challenges pending to be solved for this concept to be converted into a real solution. It is worth mentioning that although we have tried to include as many of the options and to meet characteristics similar to a professional mechanical ventilator, our objective was to build a simplified, easy- and economical-to-build apparatus that, when fully developed, could potentially be of benefit to patients in need for mechanical ventilation in a circumstance in which no other option can be offered. We also want to make a clear statement that the devices presented here:  
1. Have not been approved for use by any health regulatory agency or homologous institution.
2. Have not been tested on humans or other animals, and that all tests have been carried out with mechanical and electronic equipment only. No clinical or preclinical trials have been conducted or approved up to the date of this publication.
3. We strongly discourage any attempt to use the devices presented here on humans. Its replication should only be for the purpose of further investigation and development.  
Manually pumped ventilators have been used in the past to cope with epidemic-related patient surges [2]. It is worth noting that pushing mechanisms for a bag-valve ventilator is an approach that has been pursued by various groups around the world both in the past, mostly as an academic exercise [3; 4; 5]. Yet, in recent days many groups around the world have taken this concept as a possibility to cope with the current crisis [6; 7; 8; 9; 10]. It is worth mentioning that our designs might have similarities and face similar deficiencies to other bag-valve pushing mechanisms. For some of those developments detailed construction schematics and other detailed information have been made available to the public.