Gravity Ventilator — COSMIC Medical

Positive Pressure Ventilation

Gravity Ventilator (gVent)

Full design specifications, instructions, and testing data are available on Github.

The Idea

In February 2020, amidst the CoVid-19 pandemic, concerns about a global shortage of ventilators began to surface and these worries rapidly became a reality. We sought to find a local solution to the rapidly evolving crisis, working alongside the hundreds of open-source projects worldwide, aimed at tackling the same problem.

We believe that we add a novel solution to an evolving landscape of low cost ventilators. Built using readily-available materials, our aim was to produce a device capable of being produced at a sub-$100 price point for low-resource settings, as well as a more robust model, both founded using the same principles.

Modern commercial ventilators are complex machines with specialized components. According to the Department of Health and Social Care guidance statement on Rapidly Manufactured Ventilator System Specification (20/03/2020), ventilators must meet certain criteria to be considered “clinically acceptable”.

RMVS-compatible ventilators must be capable of providing one of two modes of ventilation. The first is mandatory ventilation, wherein the patient is completely sedated, and all work of breathing must be done by the ventilator, according to preset criteria (e.g. tidal volume, respiratory rate, E/I ratio). Supportive ventilation, on the other hand, is used when the patient can do some work on their own. The machine must be able to sense when the patient is attempting to inhale (and provide inspiratory support), and when the patient is exhaling. We aim to accomplish both.

DISCLAIMER: At this point, this device is NOT medically approved for human use, and as such, improper use can result in harm or death of the patient. It is still in its development stages and any use in the clinical setting should be under the strict consultation and supervision of qualified healthcare experts and/or engineers.

The Design

How does it work?

The basis of the gVent system is gravity, water, and two cylindrical vessels are fitted together to create a pressurized system. This pressure can then be used to ventilate a sick patient. The two vessels are each sealed at one end. The larger vessel is filled with water; the smaller vessel is placed inside the larger vessel.

Air is then introduced into the system from the hospital's gas outlets. A clinician can thus control the FiO2 by titrating the amount of hospital air to the amount of delivered oxygen. As this pressurized gas builds up in the system, the top cylinder is displaced upwards from its resting position, commensurate to the weight of the top cylinder (which can have weight added to adjust the pressure).

To deliver air, a valve is opened, releasing the pressurized air/O2 mixture through to the intubated patient. With the valve controlled on an electronic circuit, the operator has the ability to control important respiratory parameters, including respiratory rate, I:E ratio, and the volume of air delivered to the patient.

Maintenance and cleaning are relatively simple. The majority of the main ventilator components are assembled with un-plasticized PVC, an inert, chemically resistant substance. Insertion of parts can be accomplished through plastic welding, PVC glue or friction fitting with Teflon tape. All of these are suitable for drinking water purposes. The only interface between air going to the patient and the outside environment is through the water in the system. As this leads to the small potential for contamination in the system, this water is constantly cleaned and sanitized throughout the use of the ventilator, by using UV sterilization or a concentrated saline solution .

What stage is this ventilator at?

The ventilator prototype was built with assistance at Iron Mountain Welding Ltd., where in-house designers helped create the CAD drawings and the v3 prototype in collaboration with the COSMIC group. With the integration of an appropriate microcontroller, the system can sense pressure and volume. Hence the system can be patient triggered and gives pressure controlled ventilation. Additional modes of ventilation can be added with further code.

What features make the gravity vent unique?

One of this system’s greatest strengths is its ability to give constant inspiratory pressures, which greatly reduces the risk of barotrauma which is inherent in many low cost ventilator designs. This constant plateau pressure, which mimics a commercial ventilator’s air delivery, has been a popular feature among the end users who have evaluated our device, including respiratory therapists, anesthesiologists, and intensivists. We feel that this unique and reliable method of delivery sets this ventilator apart from many other designs.

Any data on reliability?

Although we have created multiple prototypes of the gVent system, we continue to refine the technology and manufacturing in order to provide a safe and reliable option for users of this system. A functioning prototype was subjected to initial testing at the Vancouver General Hospital Simulation Lab’s lung compliance testing unit. We have tested and demonstrated the prototype’s proof of principle and reliability in a two three-hour test cycles, with data on important ventilator modes, parameters, alarms and more.

How much does this cost?

Currently the system costs approximately $400 to make, but we anticipate a significant price reduction with larger scale manufacturing.

Design Specifications

How well can it ventilate a patient?

Inspiratory pressure range: 16 -40 cm H2O
Maximum flow rate: 56 SLP
Maximum tidal flow: 1.955 L
PEEP range: 5 - 25 cm H2O
Respiratory rate range: 5 - 60 bpm
I : E range: 1 : 1 - 1 : 5

Can the FiO2 be adjusted?

Yes. We can add a Y connector at the wall ports. Adjusting the respective flow rates of hospital air and oxygen allows for specific titration of FiO2.

How is infection risk of the water basin mitigated?

Currently we filter the water through a UV filter. We are also exploring options to minimize microbial growth potential with concentrated saline.

*What does the complete ventilator to patient circuit require?*

Is there a pressure control mechanism incorporated into the device?

The system is inherently pressure limited in that bubbling occurs where the water seal is broken. The point at which this bubbling begins indicates the maximum pressure the system could administer, as limited by the height and weight of the upper column.

What alarms are intrinsic in the system?

Pressure and flow sensors allow for high and low pressure, tidal volume and minute ventilation alarms. The design incorporates a relief vent which limits potentially traumatic pressures above 40cm H2O.

FAQ

+ Who are you?

We are a group of 20+ engineers, physicians, students and other professionals based out of Vancouver, Canada.

+ Why not stick with the more common ambu-bag ventilator style?

gVent has a number of advantages over the ambu-bag design. First, the built in constant-pressure feature allows for reliable delivery of air to the patient in a physiologically compatible manner. This gives breath in the same manner as one of the most common air delivery methods seen with commercial ventilators. The second issue with bags squeezers is the durability. A mechanical squeezer will hit a bag in exactly the same pattern 12-20 times a minute for weeks. They simply aren't designed for this.

+ Can air really power most of your ventilator?

Medical Air and Medical Oxygen is supplied throughout all modern hospitals. This air is supplied typically supplied at 45-50psi and has multiple safety checks built into the design to ensure reliable supply to patients.. All hospital beds have, at a minimum, one air and one oxygen supply port, and these can be readily split. Our system requires less than 1psi to function and 50psi from the wall port is able to easily supply the system’s needs.

+ Aren’t those high pressures dangerous? Where is your pressure release valve?

Despite the wall having high delivery pressures, the design of our system is such that it can never generate higher pressures than what it is set to. In the event that excess air is added to the system, it is able to escape by bubbling through the center vent. This ensures a constant pressure that is no higher and no lower than the set rate.

+ What modes can the ventilator not do?

Volume controlled modes inherently have variability in pressure throughout the inspiratory cycle. As a result, this ventilator is unable to ventilate in a classic volume control mode. However, it can still ventilate to specific volumes, but it will have a plateau pressure waveform.

+ What is the most difficult item to source in the ventilator?

The only item that is not readily available at large quantities is our sensor. However, this is not a unique problem to our ventilator. Any ventilator that is able to make decisions based on flow, volume, or pressure would need these items. We feel these can likely be sourced from non-medical components, but we wanted a highly reliable sensor to be able to confirm our values.

+ What about infectious concerns with the water reservoir?

Because the reservoir only receives fresh air, there no patient-related soiling or contamination of the resevoir. The 10L reservoir of water can be kept clean with a number of options, which include UV sterilization, use of a high concentration saline solution, flushing of the water system, or low concentration chemical sanitization.