Next, the existing Internet and gray literature will be reviewed for open source ventilator projects and designs. Lastly, as this is a rapidly evolving area, future work will be described to enable wide-spread mass distributed manufacturing of open source ventilators to fight against the current COVID19 pandemic as well as for future pandemics and to provide the devices to low-resource regions of the world that are underserved even in normal times.

Of these enabling technologies, the most advanced is the fused filament fabrication (FFF)-class of desktop 3-D printers that have spawned from the self- replicating rapid prototyper (RepRap) project 64 – 66 . With the distributed manufacturing model, designs are downloaded even in remote areas and are manufactured on demand as needed 67 from readily available (and possibly recycled 68 – 80 ) materials. These 3-D printers are, in general, not particularly fast when making products, but with tens of thousands of 3-D printers already strategically deployed all over the world 81 , they have the capacity to fabricate an incredibly diverse and large range of products (growing exponentially) 82 , which have already been shared with open source design licenses. Here, the potential will be analyzed for hardware that can be as-much-as-possible digitally manufactured using accessible low-cost fabrication tools like RepRap-class 3-D printers and then readily constructed from widely accessible materials and simple tools (e.g. DIY hardware store sourced along with Arduino-class microcontrollers). RepRap technology in particular is stressed because designs in that ecosystem are already frequently shared, enabling true distributed manufacturing by making use of manufacturing equipment near the point of use. There are, however, many other means of open hardware-based digital distributed manufacturing approaches including CNC mills, laser cutters, engravers, and etchers and other digitally controlled fabrication tools. As pointed out by Mohammed 83 many of these tools would overcome limitations of 3-D printing (e.g. speed of replication for flat parts are more easily cut from stock with a CNC tool using subtractive manufacturing than 3-D printing based additive manufacturing).

Fortunately, with the recent development and widespread deployment of open source small-scale manufacturing technologies 33 , 34 , there is now another way – mass distributed manufacturing 35 – 38 . In this new model, designs are developed and then shared with open source licenses freely on the Internet so that others can simply download and replicate the design on their own equipment, even at the household scale 39 . There has been tremendous and ongoing success of open source scientific hardware proliferation 40 – 45 , where lower-cost and superior-functioning custom equipment as compared to proprietary scientific tools 46 – 49 . Based on such scientific hardware results, there appears to be a significant opportunity to apply open source design principles 50 and mass-scale collaborative distributed manufacturing technologies to make medical equipment 51 – 54 . In the current situation, this would at least partially overcome medical supply shortages 55 – 60 in general, and specifically for ventilators 61 – 63 .

Coronavirus disease 2019 (COVID-19), caused by a novel coronavirus (SARS-CoV-2), is in part so dangerous because it threatens to overwhelm our medical infrastructure at the regional level, causing spikes in mortality rates 1 – 4 . Within the medical infrastructure, there are critical technologies that are generally available, but simply do not exist in a high enough density to handle the excessive volume of patients associated with pandemics 5 . Thus, people die unnecessarily throughout the world because of a combination of COVID-19 infections and the lack of access to some of these technologies 6 . Ventilators are an example of technologies that are currently in critical short supply 7 , 8 . Mechanical ventilators are essential for treating both influenza and COVID-19 patients in severe acute respiratory failure 9 , 10 . Past studies have shown that intensive care units (ICUs) will not have sufficient resources to treat all patients requiring ventilator support during a massive pandemic 11 – 13 , and ethically challenging triage 14 , 15 would need to be used to decrease mortality over first-come first-served basis for ventilator allocation among patients. Some work has shown promise for using a single ventilator to support multiple patients during a disaster surge 16 – 18 . In addition, it has already been shown that 3-D printed manifolds can assist with rapidly deploying this solution and there are open source designs 19 . This is not necessarily straightforward 20 . Although some countries, like the United States, have stockpiles of ventilators 21 , there is consensus that there is not enough supply for serious pandemics 22 – 25 and that rationing would be needed 26 . The current medical system relies exclusively on specialized, proprietary, mass-manufactured ventilators from a small selection of suppliers. This supply model clearly fails when there is a sudden surge in demand for a relatively low-volume specialty product such as ventilators in a pandemic as analyzed here. The vast majority of medical equipment is heavily patented by a few specialty medical firms that sell small volumes because during ‘normal’ times, a medium-sized hospital only needs a handful. These firms have historically aggressively protected their intellectual monopolies 27 , 28 to the detriment of human lives. In addition, non-practicing entities continue to attempt to actively prevent medical treatments from being deployed, even during the current COVID-19 pandemic 29 . Putting aside the absurdity of patenting and then obstructing others from using obvious inventions in normal times 30 – 32 , in the wake of a pandemic where millions of lives are at stake, it is intuitively obvious that this type of greed is no longer acceptable.

Analysis of literature

Oxygen therapy coupled with mechanical ventilation is meant to support patients so that an adequate oxygen saturation (>88%) in arterial blood is maintained85. The mechanical repository cycle has four parts: 1) inspiration, where the exhalation valve of the ventilator is closed and the ventilator uses pressured air to cause gas to flow into the lungs; 2) cycling, where changeover from inspiration to expiration occurs; 3) expiration, where the main ventilatory flow is interrupted and the exhalation valve opened to allow gas to escape from the lungs, and 4) triggering, where the changeover from expiration to inspiration occurs. According to Andreoli et al.85, mechanical ventilators are classified on what factor terminates inspiratory flow, as follows: 1) pressure-cycled ventilators terminate flow when preset pressures are reached in airways; 2) volume-cycled ventilators provide a set volume of gas to the patient over a range of pressures (but a maximum pressure is set to avoid damage to the patient’s lungs during delivery of the set tidal volume); 3) time-cycled ventilators set tidal volume by setting the inspiratory time and flow rate; and 4) flow cycled ventilators, where the inspiratory flow is terminated when the inspiratory flow rate drops below a specific level. The most common commercial modes of mechanical ventilation both provide a specified number of breaths per minute (BPM) and are 1) synchronized intermittent mandatory ventilation (SIMV) where patients can take additional breaths over the set rate and 2) assist control (AC) that uses triggering so that if the patient makes an effort to breathe, it helps them, and if not, it maintains the set rate. These modes can be used alone or in concert with 1) continuous positive airway pressure (CPAP), which uses a high-pressure reservoir and constant flow of gas that exceeds the patient’s needs; 2) positive end-expiratory pressure (PEEP), which increases the residual reserve capacity and allows for many alveoli and small airways to remain open that would otherwise close off; or 3) pressure support ventilation (PSV), which adjusts the pressure on the fly as the patient breathes to maintain a preset inspiratory pressure. For those designing open source ventilators using any of those modes and methods, there is a good base of established literature to draw upon. The classic background is available in Hess, et al.’s 1996. Essentials of mechanical ventilation86, Tobin’s 2010 Principles and practice of mechanical ventilation87, and Owens’ 2018. The Ventilator Book88. In addition, Chapter 4 in the openly accessibly book Equipment in Anaesthesia and Critical Care: A complete guide for the FRCA, provides a good starting point to help makers understand existing designs and terminology for ventilators89. Texts are available for the use of a ventilator for the standard of care of patients with acute respiratory distress syndrome (ARDS)90, ventilator management for the NIH91, and the practical use of oxygen for patients92. A 2017 state-of-the-art review of mechanical ventilation is presented by Pham et al.93 It provides basic schematic diagrams for all of the main classes of commercialized ventilators and reviews their pros and cons.

There exists some confusion on the meaning of the term ‘open source’, which must be clarified to understand how the ventilator designs are evaluated in this review. Ventilators are hardware and thus to be an ‘open source ventilator’, a device must meet the principle and definition provided by the Open Source Hardware Association (OSHWA), specifically:

“Open source hardware is hardware whose design is made publicly available so that anyone can study, modify, distribute, make, and sell the design or hardware based on that design. The hardware’s source, the design from which it is made, is available in the preferred format for making modifications to it. Ideally, open source hardware uses readily-available components and materials, standard processes, open infrastructure, unrestricted content, and open-source design tools to maximize the ability of individuals to make and use hardware. Open source hardware gives people the freedom to control their technology while sharing knowledge and encouraging commerce through the open exchange of designs.”

Thus, a ventilator (or any other hardware) is not ‘open’ unless it both provides all of the source (as detailed above) to replicate it as well as shares it with a license that protect others’ freedoms to make or use it. There are some flawed uses of this term from two types of designers. The first type consists of designers claiming they have open source projects before they have shared the code. This is the most rampant in the current ventilator design community with many pretty renderings and high-production value videos with nothing of technical value behind them (i.e. there is no source to replicate the machine available). Most of these designers may have good intentions but the source code may never materialize. Perhaps the most highly publicized case with a good ending was of Medtronic, a large commercial ventilator company, which first announced an open ventilator project on 3-29-2020, but did not release the CAD, BOM, software, etc. to actually fabricate it. Medtronic has now released these documents under a permissive license for their Puritan Bennett 560 ventilator, which already has been commercialized ($10,000 and first introduced 10 years ago) and received FDA approval. Although these design files have been accessed over 90,000 times, this system is designed for mass manufacturing and will likely only be manufactured in that context. All ventilators made from the designs must be labeled with a warning noting that it was built in response to COVID-19, and is only to be used to address this pandemic. Thus, it should be stressed that thisa permissive license is not an open source license. The license only covers addressing the current global coronavirus pandemic, and its term ends either when the World Health Organization’s official Public Health Emergency of International Concern (PHEIC) is declared over, or on October 1, 2024, whichever comes first.

The second type of designers who misuse the term open source, have shared their code, call it ‘open’ but do not actually provide open hardware licenses or they specifically restrict the freedom of others from using it. This confusion is observed throughout the community working on COVID-19-related designs. An example of this confusion is with the ‘make the masks’ website that hosts a 3-D printable mask. They state: “These designs have provisional patents in place, and are intended for this goodwill campaign during the course of COVID-19. If you choose to pursue injection molding, it must be a not-for-profit venture that operates at cost to serve your local community. No license agreements will be awarded to for-profit ventures working to manufacture and distribute this product.” Specifically, in their FAQ it states“…we would like to stress the fact that these files have provisional patents and are for open source use only.” This is not what open source means and there is no ‘fair use’ provision for patents as there is with copyright94. In addition, although the STL files are available for replication one must email them for the CAD. This Montana Mask/Billings project is thus not open source by the OSHWA definition. Although it is unquestionably doing some good for the global community because some of the files have been released for distributed manufacturing, it is clearly restricting the end use. The masks take over 3 hours to print on standard 3-D printer and demand for such personal protective equipment (PPE) in some communities outstrips their local supply of 3-D printers. If manufacturers wanted to injection mold them at scale and sell them for a profit while increasing their accessibility and helping people, they are explicitly denied the freedom to do so.

The application of both of these fundamental misunderstandings of what open hardware are have been termed ‘open washing’ or ‘fauxpen’95. There has thus been a call for open source hardware standardization of practices96 in a way that legally prevents such misuse of the term.

Existing peer-reviewed literature The peer-reviewed literature itself is currently limited, but there has been some research on low-cost ventilation, even if the source is not available. First, a field portable ventilator system for domestic and military emergency medical response has been conceptually designed, but does not include enough information to construct it (e.g. the software was written in assembly language and not shared)97. This article does contain design considerations that may be useful for open source designers. A new, compact and low-cost mask respirator concept has been developed and prototyped successfully98. The blower unit was able to provide adequate ventilation to the test lungs. In addition, the integrated sensor for airway pressure was able to detect airway occlusion and leakages. It is a relatively low-power device and could be operated wirelessly with batteries. It provides a cross-sectional view of the blower unit and some details, but again, not enough to be considered full open hardware or to be easily replicated. It should be noted, however, that many of the components are within RepRap-class 3-D printing capabilities. In addition, research has been undertaken on a pre-stage public access ventilator (PAV)99. The PAV is made up of several low-cost technologies including a self-designed turbine and a range of sensors for differential pressure, flow, F i O 2 , F i CO 2 and three-axis acceleration measurements. The PAV was tested under three conditions to show that it was adequate for an automatic emergency system: 1) pressure-controlled ventilation (PCV), 2) PCV with controlled leakage and 3) PCV with simulated airway occlusion. The PAV was tested for and showed effective ventilation for tidal volume, breathing frequency and inspiratory pressure. Similarly, there has been a proposal to replace artificial manual breathing unit (AMBU) bags with electric blowers to act as emergency ventilators100. In contrast, another approach is to build a low-cost ventilator utilizing an AMBU bag that is not based on constant blower use101. The study by Mukaram Shahid showed the AMBU setup was able to perform all the functions of a conventional commercial ventilator for a far lower cost (<$100US excluding labor). The automated AMBU device was able to adjust the breathing rate and the volume of the air, which is comparable to older ventilators. However, it was also able to regulate the inspiration to expiration ratio and PEEP rate. Shahid’s system comes with two modes: 1) mandatory ventilation (as in older models) and 2) assisted ventilation (as with most current systems). Thus, the medical personnel can choose to use either the built-in triggering mechanism (assist boosted mode), which alters the respiration pattern once it detects a change in air pressure, or set a time interval for the respiration pattern. The article contains pictures, an electric schematic, a control loop diagram, and very basic results. Again, this can be used as starting point, but there is not enough shared to replicate in the open hardware fashion. Next, a low-cost ($420 prototype) portable mechanical ventilator was designed and prototyped that delivers breaths by compressing a conventional bag-valve mask (BVM) with a pivoting cam-actuated arm pushed by an electric motor102. This eliminates the need for a person pushing on the BVM, which is generally viewed as only a short-term solution. This system uses knobs to determine the tidal volume appropriate to the patient (usually 6–8 mL/kg of ideal body weight), adjustable BPM of 5–30, and inhalation to exhalation time ratio options of 1:2, 1:3 and 1:4 and a minimum respiratory rate103. This design is run with an open source Arduino micro-controller104 and the article provides enough details to be used as a guide for others to build a similar device, but not the full plans, code, etc. needed to qualify as an open source hardware device. One of the most relevant designs is a pneumatic ventilator specifically designed for pandemics, which has a low oxygen consumption105. In this study by Williams et al., they describe and test three simple, pneumatically powered, low oxygen-consumption ventilators. The three designs were tested for different lung compliances (i.e. different ventilator workloads) on the delivered F i O 2 and oxygen consumption. They used a commercial mechanical test lung for these tests (Vent Aid; Michigan Instruments Inc., Grand Rapids, MI, USA). The results of this study support the potential for mass distributed production of a low-cost, gas-powered, volume-controlled ventilator with a low oxygen consumption (anywhere with oxygen at 2–4 bar). The designs could alternatively be operated on hospital compressed air. The single use, self-inflating bellows system prevents cross contamination among patients. In addition, the system possessed one-way and safety overpressure valves, which could be incorporated into other designs. The designs are in part supplied including basic principle schematics, an example BOM, but falls far short of what is expected for a complete open hardware design. A large multidisciplinary and international team has just published (currently accepted, available in pre typesetting form) in a study on a low-cost, easy-to-build non-invasive pressure support ventilator meant for under-resourced regions106. The design is based upon using off-the-shelf components and is comprised of an open source Arduino Nano for control, high pressure blower and two pressure transducers. It was bench-marked against commercial systems. Their supplementary material also covers the testing with healthy volunteers, but more importantly, has the basic layout of the device, PCB and circuit schematics including source files, a BOM, STLs for the 3-D printable case, description of the algorithm and the Arduino ino file, and a user manual. This device’s source is available and would represent a method to fabricate a ventilator for <$75, which has already been vetted by medical professionals. There are several interesting points about the approach used106. First, Garmendia et al. took the non-invasive medical approach, which is particularly well suited for both low-income countries107 and also perhaps during pandemics where even the wealthiest nation’s medical systems are strained. By focusing on off-the-shelf components their design could be easily replicated. In ‘normal times’, this approach is second only to systems that can be completely digitally fabricated with local resources. In pandemic situations, it exposes why it is important to have many such designs, as the global supply chains have been disrupted108–110. Normally, in the U.S. to replicate Garmendia et al.’s design based on the documentation provided would only be expected to take a few days. With the disruption, numerous makers have been having trouble sourcing supplies in the U.S., and the lowest-cost blower following the Garmendia et al. design has an estimated shipping of 8–18 days on 4-28-2020 in the U.S. There are alternatives for providing this function (both suppliers and devices), which is why it is important to have a ‘diversity of solutions’62 with as many alternative suppliers, components and possibly even digitally manufacturable parts as possible (e.g. there are already several 3-D printable centrifugal blowers developed, which would demand future work for this application). Lastly, this design did not appear to have a license associated with it being a purely medical science publication. Even the Arduino code, which did have an author information for help, did not contain any license. This could hamper rapid deployment in some contexts as not explicitly indicating a license declares an implicit copyright without explaining how others could use the code111,112. There are also completely different approaches to the design of a ventilator, such as the high-frequency oscillatory ventilator113, but only basic design schematics and preliminary testing is provided. Thus, within the peer-reviewed literature, most of the quasi-appropriate ventilator devices use a standard ventilation bag that is cyclically compressed by either an electromechanic or pneumatic setup and controlled by a microcontroller. Fortunately, the most complicated part of these designs is the controls, which is made accessible by the maturation of Arduino-based microcontrollers that can actuate and sense over a wide array of accessible and already-developed technologies (e.g. code libraries are available). It should be noted that most of the low-cost options in the literature used the bag approach, but that modern commercial ventilators are generally not manufactured with bags, bellows or pistons due to performance concerns. These concerns may be overcome by the nature of a pandemic, as well as by replacing low-cost components during failure, but this does indicate failure detection is warranted and certainly preferred in an open source ventilator design.