# Regulations [RMVS001 Specification Issued by MHRA][1] <br /> ## Highlights <br /> **Ventilation** * *Mandatory* mode must be either (ideally) Pressure Regulated Volume Control, or a pressure controlled ventilation (PCV) or a volume controlled ventilation (VCV). * *Optional* pressure support mode for those patients breathing to some extent themselves, e.g. BIPAP or SIMV-PC. The user sets an inspiratory pressure and an expiratory pressure. The ventilator can sense when a patient starts to breathe in and apply the inspiratory pressure, then sense when the patient starts to breathe out and apply the expiratory pressure (this pressure is still positive but lower than the inspiratory pressure). * Inspiratory airway pressure. * Positive End Expiratory Pressure (PEEP). * Inspiratory:Expiratory ratio (I:E). * Respiratory rate. * Tidal Volume (Vt). **Gas and electricity** * **Infection control** * **Monitoring and alarms** * **Miscellaneous** * Intuitive interface * Robust design ## Testing procedure [ISO 80601-2-12:2020][2] Medical electrical equipment — Part 2-12: Particular requirements for basic safety and essential performance of critical care ventilators. Compliance with the essential safety standards must be demonstrated for patient safety. ### Comments from Ross If volume driven: can the ventilator supply 250ml to 800ml in each breath, what is the mean volume supplied and standard deviation in 100 breaths? What is intervals we can use on the ventilator? I would say that if you could make it adjustable to at least 25ml steps that would be acceptable. In volume or pressure driven: it would be excellent to get pressure curves that include peak inspratory and plateau pressures and then average them with standard deviations over maybe 100 breaths. It looks like this is possible with the test lungs! Respiratory rate: mean and standard deviation at 10breath per minute and 30 breath per minute and maybe one or two settings in between. Durability testing: I would aim for >7days as a mandatory and >14days as a huge plus. This is the question of how can we test these machines for durablilty and not have it take 14 days, I have hear some people are increasing ventilation rates so it shortens the time span of testing... If alarms are included: Can the machine reliably alarm if ventilation is stopped? If pressure relief is included: can the machine prevent pressures from being built up which can cause barotrauma? If failure is induced will the the pressure relief system work reliably 100% of the time in 10 tests? ### Comments from Mike The test lungs with pressure/volume monitoring are ideal, both for adult and pediatric parameters. For now I would focus primarily on adult, especially since the RMV specs do not allow ventilation of children/infants. Clinically useful information: 1. Ideal tidal volumes are no greater than 6-8 ml/kg (the RMV manual mentions 6 ml/kg) to avoid overdistension. 2. Tidal volumes for adults (using volume ventilation modes, including PRVC) then would typically be 250-300 ml for smaller adults, and up to 800-1000 for larger adults. 3. Peak pressures adjustable by 1 cm increments, typically we don't exceed 30-40 cmH2O. Mechanical pop-off at 80 is a great failsafe. 4. PEEP from 5-20 is suitable for most patients, but I would allow adjustment by 1 cmH2O increments rather than 5. 5. Rates for most adults should be adjustable from a low of 6 to a high of 30, possibly higher, but if you have a rate greater than 30 and any expiratory resistance you run the risk of "stacking breaths" when inhalation occurs before exhalation has completed. 6. Pressure-volume curve display is extremely helpful to monitor lung function, both to assure that PEEP is adequate to prevent alveolar collapse at low volumes and to prevent over-distension at higher volumes (Law of LaPlace). 7. Minimizing resistance and compliance in the system are very important. The alveolar time constant varies widely, and diseased lungs often have high resistance, high compliance, or both, so the system must have low resistance and low compliance in order for the ventilator to function properly (stiff, short tubes, minimal connections that cause luminal narrowing or turbulance - Hagen–Poiseuille equation). ### Comments from Adam's friend If there is not access to a ventilator then a bag valve mask is used - he said the bag valve was an interesting and good idea for a vent as a last resort device The main reason bag valves not sustainable for more than a few hours is that they cant detect how much volume of gas or concentration of O2 is needed by the patient A promising thing is that in his experience patients were either sick for days(4-5+) needing a ventilator or relatively shorter - a day - before they could handle not having one. So if we can aim for 2-3 days reliably, the OS version could have a huge impact. --- # Design references 1. [MIT Emergency Ventilator (E-Vent) Project][3] 2. [OpenLung BVM Ventilator][4] 3. ... --- # Electronic components 1. Arduino 2. LCD display 3. Button + Encoder 4. Power supply 5. Air pressure sensor --- # Software architecture ### Control system design for Arduino @[osf](xf2nj) ### Minimum viable circuit (will be updated) @[osf](5tykv) ### Bill of materials (will be updated) | Component | Amount | Price per unit, $ | | ------ | ------ | ------ | | Arduino Nano | 1 | 3.4 | | Stepper motor Nema-17 | 1 | 8.0 | | Motor driver A4988 | 1 | 1.8 | | 16x2 LCD display | 1 | 4.5 | | Rotary encoder | 1 | 1.6 | | Buzzer | 1 | 0.6 | | BMP280 barometric sensor | 2 | 2.8 | **TOTAL = $25.5** # Calculations @[osf](knzxa) # Feedback response @[osf](8fv6j) # LCD display @[osf](6bj7t) [1]: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/874279/RMVS001_Rapidly_Manufactured_Ventilator_Specification__PDF.pdf [2]: https://www.iso.org/obp/ui/#iso:std:iso:80601:-2-12:ed-2:v1:en [3]: https://e-vent.mit.edu/ [4]: https://gitlab.com/open-source-ventilator/OpenLung