Follow the rapid development of this project, which started March 16, 2020.
March 16-22, 2020
Researched existing solutions for patient ventilation, both in-hospital and in rescue situations. Developed an idea to support multiple patients from a single air source (pump), with solenoid valves and digital control timers employed to direct air to multiple groups of patients according to a prescribed respiratory rhythm. Air pumps can simply produce forward air. The flow coming from them should not be reduced or restricted (i.e. “deadheaded”) in order to avoid overheating and reducing the life of the pump. Compared with an ambu bag style ventilator, which provides forward air only when the bag is squeezed, pumps produce air continuously, thereby offering potentially increased efficiency. While one group of patients is exhaling, flow from the pump can be re-directed to another group of patients who are inhaling.
For purposes of a prototype, large commercial aquarium pumps were selected as the primary air mover. These devices provide oxygenation to large, exotic fish aquariums and are designed to operate continuously. Reliability and failure modes were evaluated. The need for enclosing and cooling the pumps to prevent overheating was established. A basic design was drafted and parts for a prototype were procured. Since this is to be a field unit, maximum power demand of 400 watts was established (able to be powered by a light pickup truck’s auxiliary AC power supply). The unit should be housed in a durable enclosure (utility toolbox system by Milwaukee Tool Division was ultimately selected and permission obtained via phone from Bryan Sanchez to use branded boxes without removing the Milwaukee branding. Bryan is their Director of Business Development). Also notified Group President, Milwaukee Tool Division, Steven P. Richman of the project. He was supportive. The unit should be buildable as quickly as possible by a team with average mechanical/electrical abilities using as many off-the-shelf parts as possible. Most of the parts can be obtained at a hardware store, with exception of the programmable logic controllers and oxygen-cleaned solenoid valves.
March 22-25, 2020
Procured parts for the prototype. Began building. Created annotated photos. Posted all plans, engineering calculations, photos to a shared Google Drive (which has since been deactivated in favor of this webite). Shared the design with CU Anschutz friends and colleagues, who put it out to their networks.
March 26, 2020
Update 1- Heard from engineer, Haidar Malhas in Ghana last night — he had the following suggestion after reviewing the design and finding it essentially satisfactory. We consider this a critical update, although the anticipated port pressure from the system is low:
— SPLICE IN A PRESSURE RELIEF VALVE JUST BEFORE EACH PATIENT VENT PORT. I AM USING 1/2″ Tees inline with the PVC gate valves— bush the 90 degree port down to 1/4″ NPT and using a 1/4″ NPT 0-20 psi (0-1400 cmH2O) safety relief— It will allow you to set the valve down to a safe range in case there might be pressure fluctuations in the system. Will share photos later.
A secondary suggestion to filter the air on the output side of the pump instead of the intake side is not going to be implemented at this time since I am trying to filter out whatever COVID-19 virus particles we can (it’s a 5 micron filter). I know we can’t filter out aerosolized particles, but it is filtering moisture. I’m using a much larger filter than needed to avoid choking the pump on the intake.
I added the pressure relief ports and programmed the digital relay timer. I decided to include two identical timers for redundancy. If one fails, then the other one simply needs to be turned on. I added a folder (Video) and put a 5 minute clip on how to program the timer since it doesn’t come with any instructions. I’ll do my best to clarify that as I have time.
March 27, 2020
First test of the unit today— Digital relay timer controlling valves and redirecting flow as designed. There is now an “inhale” manifold and and “exhale” manifold with 4 vent ports on each manifold. Will flow/pressure test these later. I added the pressure relief ports on all patient lines.
Yesterday I was working on built-in redundancy. Here is were we are with that:
1. In case the primary pump fails, a second pump is provide. Simply plug it in and switch the air supply line from primary to secondary. While the pump is running, connect the intake filter to the new pump (simply move the intake tubing to the new pump from the old).
2. I added a second digital relay timer programmed identically to the first. Simply turn on its power supply and hit the start button. It will control the switching solenoids the same way the first one did. If the doctors have re-programmed the “inhale” and “exhale” times, they will have to do that for this timer as well.
3. I added a 5 minute video on how to program the timers (see previous day update).
4. Added tubing adapters to the end of the manifold opposite the solenoid valves. If those were to fail, a person could manually open and close flow into the manifolds (one for inhale, one for exhale) while the solenoids are being changed. Include two solenoids (one normally open, one normally closed) for each unit, so they can be swapped out while the person is being manually vented.
Created 8 videos of the testing from today. Promising results. Still awaiting a second cooling fan and the pressure relief valves. Planning to leave for San Fran on Sunday or Monday to deliver the unit to UCSF.
March 28, 2020
Six port testing was done. Unit can supply two manifolds with six ports on each at 2.5LPM; however you’ll need to add an additional 4-port manifold to each side, connect it to the first, and turn off two of the ports. The marginal cost to do this is very low per patient added however!! Delighted that you could provide respiratory support for 12 patients on this one pump (supplying six at a time, out of phase). Added a couple more videos.
March 29, 2020
Worked to get word out. Spoke with Milwaukee Tool senior leadership about use of their boxes; interacted with senior leadership at CU about best steps to move forward. Planned to deliver the first unit to Dr. Whetstone in San Francisco on Wednesday 4/1.
March 30, 2020
Drove to Utah. While driving, thought of way to add a ventilation mode that would provide Inhale:Exhale of <1 (in other words Inhale time less than exhale time. This is doable. It will require using the second timer in the circuit and not as a backup. Will sketch this tonight and post. Unclear if this mode will be needed. Will ask Whetstone when I get to San Fran.
March 31, 2020
Posted the sketches I made last night for the I < E timer modes. It is definitely possible but you will lose your fail safe ability to manually operate valves (because it requires 3 patient vent manifolds). You will need to set the second timer such that time on and time off is evenly divisible into those of the first timer. I demonstrated this with a 1:2 Inhale:Exhale logic diagram— it requires the other two patient manifolds to operate in a binary 1:1, 1:3 mode (which alternates)— so the net breaths per minute to the patient and net volume per breath are the same. Take a look at the photos in the 31MAR2020 folder of the “Build…” folder (under “Images”). That should make it clear.
Reorganized all the build photos to make more logical. Heading to San Fran from Utah.
April 1, 2020
Exuberant day in San Francisco. Met with Dr. Whetstone (from UCSF) to review assembly, operation of the Field Ventilator unit. Discussed respiratory modes 1:1 IE ratio, 1:2 IE ratio (which he preferred and requested be implemented). Made the necessary modifications to the unit in order to achieve 1:2 Inhale/Exhale ratio. This meant adding a second digital relay timer to the unit; re-programming the first timer; adding two solenoids, and an additional patient vent manifold. I will post all videos and photos from this when I’m back in Denver. But the net of this is that we tested the modified unit and found it can push air to 12 patients on a 1:2 I/E ratio for 4; and a 1:1/1:3 I/E ratio for the other 8. It is important to note that both groups of patients receives 20 Breaths per minute and has a positive net I/E ratio of 1 second of inhalation to 2 seconds of exhalation. At 2.5 LPM of flow (without added oxygen), this provides 125 mL of air per breath.
Note: an improved programmable logic controller was later substituted for two digital relay timers that eliminated the need for 1:1/1:3 E/E ratio.
A few new images of the final device are included in the Build Folder. The videos we took today in general are large and I may need to break them into sections when I get home before sharing them to the Drive.
April 2, 2020
This morning we received from the UCSF team another query as to whether the unit could be used as an early intervention device in “CPAP mode”— providing continuous positive airway pressure to patients who are not yet in a situation requiring invasive respiratory support (i.e. intubation). This is how the unit started. Essentially using it that way means bypassing the timers and solenoid valves, connecting the air tubing directly to the patient vent manifolds from the pump and adjusting flow rate accordingly. As tested, the unit can provide continuous flow of 6 liters per minute to at least 8 ventilator ports. The simplest way to achieve this is to use Patient Vent Manifolds with normally open solenoid valves (which I’ve designated Manifold 1 and Manifold 3 in the Electronic Schematics); remove air supply to the normally closed solenoid at the “Bridge” and the normally closed solenoid valve at the Patient Manifold 2. Reconnect the tubing supply that had been going to Patient Manifold 2 up to the Air supply Tee from the Pump. Turn both digital relay timers off (lower right button on each). You are now providing air to the two manifolds with the gold normally open solenoid valves. Attach your CPAP vent hoses to those manifolds and you will be flowing continuous airway pressure to those (eight) patient ports.
Added the electrical schematic for converting the Field Ventilator Unit to a 1:2 Inhale/Exhale ratio.
April 3-4, 2020
Traveled from San Fran back to Colorado. Prototype #1 left with Dr. Whetstone in San Francisco Worked with CU Chancellor’s office to plan construction of one or more units for Colorado. Upon return, discussed (with Dr. Whetstone) addition of High Flow Oxygen at variable flow rates (FiO2) to the ventilator. Completed the design for this upgrade, added the schematic and a couple additional parts to the Shared Folder. Plan is to put up the Build site at fieldvent.org tonight after review by Dr. Whetstone. Oxygen cleaned solenoid valves will need to be substituted for those used in the prototype.
April 5, 2020
Worked on FiO2 calculations and integration ports. Posted these modifications to the working website.
April 6, 2020
Ken L got the fieldvent.org site up and SSL working. We will be shutting down the shared drive so we only have to update in one place. Spoke with people who may be able to help source parts and build units; spoke with several control system and flow experts who had good inputs. We will continue to update here as design changes are integrated. Remember, the purpose of this ventilator is as a field unit for crisis intervention mode when the shortage of vents exceeds the supply– as an option for anyone who would not otherwise be prioritized for respiratory support when indicated. Thanks everyone!
April 8, 2020
Today we began building the second unit, aided by an outstanding team of engineers, flow mechanics specialists and supply chain professionals at RK Mission Critical in Aurora, Colorado. Special thanks to President and CEO of RK Mission Critical, John Marinnucci for his leadership, flexibility, people and resources to make this happen. The “Can Do!” spirit of this team is amazing. RC Mission Critical is providing the resources to build five units for the Colorado healthcare community and the people it serves. As with other areas, Colorado may be facing a critical shortage of ventilators in the coming days. Thanks as well to Plant Manager, Scott Dickerson; Pre-Construction Manager Phillip Powers; and Floor Manager, Sam Soares. Thanks to SVP and Chief Customer Officer, RK Corporate, Marc Paolicelli for putting together this team and making it happen. Finally, special thanks to CU Anschutz Medical Center Chancellor Don Elliman; and CU AMC Excecutive Vice Chancellor For Biotechnology, Steve VanNurden for catalyzing, supporting, and participating in this project.
Today Dwayne Kessinger (RK Mission Critical Engineering Manager) and I critically evaluated the potential failure modes of the ventilator as designed and prototyped. We identified better solenoid valves (Spartan Scientific later supplied a 20 Million Cycle valve built specifically for these field ventilator units) vs. the 1 Million cycle valves used for the prototype); and better digital relay timers with 100% solid state electronics to replace the existing DRT’s, which have mechanical relays and may also have limited life. We will provide specs on the new valves and controllers shortly. The valves are made by Spartan Scientific. Use of a new solid state programmable logic controller offers the possibility of simplifying the design. We will have a spec ASAP.
April 9, 2020
Today we revised the prototype to improve anticipated service life in the digital valve timers, solenoid valves and switching relays. Thanks to Dwayne Kessinger for spec’g a drop-in power module, complete with new programmable logic controller (PLC); 24V DC Power Rail, and solid state relays for each patient ventilator manifold. Thanks to Jim Koller at Spartan Scientific (Canfield) for spec’g new 20 million cycle solenoid valves. These will be custom O2 cleaned valves. Jim and company spec’d entirely new valves and promised them in under a week. Thanks as well to Jesse Davern and Zdenka Mueller at RK for their flexibility andextraordinary patience with design modifications; as well as their incredible supply chain connections/efficiency.
April 10-14, 2020
We’ve been busy building the Rev 2 vents. Working on training the RK team; building manifolds, enclosure modifications; vibration and sound damping; enclosure cooling; trying to find parts; substituting parts on the fly; training the RK Mission Critical assembly teams and Floor Manager (shout out to Sam, Danny, Leon and Cesar. You guys learn quickly and are making things happen. Thanks to Veronica and the custodial staff for clearing and cleaning the assembly area.
Between yesterday and today, also introduced a room air bypass feature to the vent. This will avoid dead heading the pump and will expand the range of FiO2 the unit can deliver. Not deadheading the pump allows the unit to run CPAP on one manifold; BiPAP on the second manifold; and 1:2 or 1:1.6 on the third manifold, where four intubated patients can potentially be supported (both requested I:E ratios by the ER physicians and respiratory therapists). The 1:2 I:E mode provides pure square wave inspiration/exhalation; whereas the 1:1.6 mode provides some clipping to the wave forms. These will be posted as soon as available. It is also important to note that running simultaneous CPAP, BiPAP and asymmetrical I:E ratios does produce fluctuations in CPAP flows, though air is always moving. 1:1.8 would also be possible, with peak flows lying between the 1:1.6 and 1:2 we have analyzed. There would also be clipping to the inhale waveforms as with 1:1.6 I:E mode.
April 15-17, 2020
Acquired parts to complete six Rev2 field ventilator units. Passed the one month anniversary date of the project on April 16. Continued to model system performance, inhale/exhale wave forms when each manifold is running different respiratory modes (e.g. CPAP, BIPAP and 1:X Inhale:Exhale). These are posted here. Developed concept of peak shifting (synchronizing the inhale of manually entered inhale:exhale and BIPAP modes to minimize manifold flow fluctuations). RK Electronics assembly personnel Ricardo, Matt and Mike joined Dwayne in assembling and testing the new power and control modules. They did a great job and even provided some video footage to help others with the build. We are withholding instructional video for Rev2 units at this time. Completed unit number 2 on 17APR2020. It will be delivered to the Pulmonology Research Lab on the CU Anschutz Medical Campus. Posted more build photos and videos for Rev2 in the Rev2 Build section of this site. Planning to complete assembly and bench testing of all six units on 20APR2020 and begin deploying the units.
April 18-24, 2020
Received a few components that were needed to complete the build of Rev2 units 2 through 7. Delivered unit 2 to CU Anschutz Medical Center Pulmonology Research Laboratory (Dr. Jeff Sippel, Associate Professor of Clinical Practice, Medicine-Pulmonary Sciences & Critical Care) for evaluation and testing. Units 3-7 should be completed this week. Unit 3 will go to UCSF for testing. UC Health Colorado Springs will receive a unit for testing by Kevin McQueen, MHA, RRT, RRT-ACCS, CPPS, CM, Director, Southern Colorado Region, Respiratory Therapy/Pulmonary Diagnostics, UC Health Memorial Hospital; and Rob Scott, BSRT, RRT-ACCS, CPFT, Clinical Manager, Respiratory Therapy, UC Health Memorial Hospital, Colorado Springs. Although the role of ventilators in helping to manage patients with COVID-19 has continued to evolve very quickly, the Field Ventilator’s viability in multiple respiratory modes as an emergency solution; and as a possible solution with appropriate modifications for developing nations with no ventilators appears sound at this point.
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The content has not been reviewed or approved by the U.S. Food and Drug Administration (FDA). Interested readers are encouraged to contact the FDA and review available FDA materials, including their guidance on ventilators as well as the Department of Health and Human Services (DHHS) declaration of liability immunity for medical countermeasures against COVID-19.
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The Authors are proud of their affiliation with the University of Colorado as alumni and, in the case of Dr. Thomas Greany, as a professor at the Anschutz Medical Campus. The Authors express their appreciation to the University of Colorado for its support of this project.