STORY :
SMART DIY Open Source Ventilator
WHY : Ventilator shortage
WHAT : DIY Ventilator with Pressure regulator
HOW : 3D Printed retro fitted Medical Ambo bags......... Very cost to manufacture.
WHO: INALI Indian start-up, 3DS Mentors and Doctors.
Main objectives
One of the most pressing shortages hospitals are facing during the Covid-19 emergency is a lack of ventilators. The ventilator are essential devices which can help patients with breathing when they face acute breathing challenges. The ventilators which are currently in use are imported and cost around USD 20,000 (Rs 15,00,000/-) each. Even few of the local made ventilators cost about Rs 7,00,000/- Our objective is to implement a safe, cost effective alternative for emergency use, which could be built quickly and deployed. We aim to make each ventilator available at affordable cost of around Rs 15,000/- (USD 200) per ventilator. We are also making completely indigenous design such that all parts necessary to manufacture such ventilators are available / manufactured locally avoiding need of any imported parts.
Project description
India is predicted to have a around 30,000 ventilators in the country, many of which are already in use. If the pandemic grows, we would soon run out of ventilators. Many Indian health-tech companies rely on international companies to design their machines, some of which are produced locally. Since the design process is not locally carried out, ability to scale these systems relies on imported parts, which are hard to get with current aviation bans in place. Hence locally made SMART ventilators are the need of the hour.
We will work with doctors/hospitals to validate the functioning of SMART ventilator - when approved, conduct patient trials on permission, under medical supervision. The Smart ventilator is designed and developed as per ISO 80601-2-80 and ISO 80601-2-79 according to WHO.
Basic Concepts of design:
Pulmonary ventilation is the exchange of air between the lungs and the ambient surroundings. Inspiration occurs when the diaphragm and intercostal muscles contract to expand the thoracic cavity - creating negative gauge pressure that causes ambient air to enter the lungs. Expiration occurs when the diaphragm relaxes and tissue elasticity causes the thoracic cavity to contract and expel air. Mechanical ventilation assists natural respiration by delivering air to the lungs and controlling its release through an endotracheal tube that is placed through the vocal cords into the trachea.
The rest-breathing rate in adults is 12 to about 20 cycles per minute. The total lung capacity of an adult male is about 6 liters but the tidal volume (exchange in each breathing cycle) is typically only about 0.5 liter, however this varies based on lung size (which correlates to Ideal Bodyweight, IBW, calculated based on height).
In Acute Respiratory Distress Syndrome (ARDS), many areas of the lung are collapsed and much harder to stretch (referred to as reduced lung compliance). This means the effective size of the lung is much smaller and attempting to give an average breath exposes the healthy portions of the lung to much higher pressures. High pressures in the lungs in turn cause barotrauma, which worsens ARDS. It is therefore critical in ARDS to measure and control airway pressures. Below is a diagram explaining different airway pressures:
The resistive pressure is an indicator of the resistance or the air passages between the pressure sensor in the ventilator and the alveoli (microscopic air sacs that make up the lungs), while the plateau pressure is an indicator of the pressure at the alveoli. In ARDS, resistive pressure is typically low, while plateau pressures tend to be high and must be carefully monitored, with adjustments to settings to reduce them.
DIY SMART VENTILATOR :
Hardware:
Connection to endotracheal tube: 15mm inner diameter universal connector (ideally slightly conical, slightly wider at the opening to allow for an easy friction-fit while being smooth to allow easy removal, ~15-20mm long)
Ventilator linkage: short-length corrugated tubing (easy flexibility but should not expand or collapse with internal pressures -100 to +100cmH2O (+/-1.42 PSI), ~50cm, 15mm outer diameter universal (cylindrical, 15-20mm long). Because this design does not use separate channels for inhalation and exhalation, the tubing should have minimal volume so as not to contribute to dead space, while being wide enough to avoid adding significant flow resistance (at least 15mm internal diameter).
In-line pressure sensor: a low-cost disposable pressure sensor capable of sensing -100 to +100 cmH2O, with a sampling rate of at least 10 times/second, ideally 100 times/second. The sensor should be shielded from moisture that condenses in the tubing. The portion that will be exposed to the patient’s exhalations will have to be disposable or easily decontaminated (if a thin, flexible diaphragm could be used to conduct pressure accurately, this may lower the cost).
In-line flow sensor: low-cost disposable flow sensor capable of sensing flows 0 to 3L/min, with a sampling rate of at least 10 times/second, ideally 100 times/second. Will be used to calculate volume delivered and detect patients taking a spontaneous breath.
Exhalation blocker: allows inhalation freely, but can be used to block exhalation temporarily for an inspiratory hold (breath hold) maneuver (see below). Can be accomplished either with a solenoid-actuated one-way valve (must default to unblocked during power failure), or a spring-loaded button that physically seals the exhalation port and activates an electronic button to tell the computer to measure a plateau pressure and alarm if blocked longer than 10 seconds.
Standard bag-valve with addition of a PEEP valve on the exhaust port.
The PEEP valve increases resistance to exhalation, allowing the maintenance of a pressure ranging from 0 to 30cmH2O (typically 5-15) against exhalation. Typically made with a spring holding the exhalation flutter valve shut until enough pressure builds up behind the valve to push it open. The spring is tensioned such that the pressure is adjustable as specified above.
Many bag-valves come with a PEEP valve, so manufacture of this piece is not a priority, but PEEP is a crucial element of ventilating patients with many severe lung illnesses.
A very fine filter (N95 spec or higher) over the exhaust port would help make the environment much safer for the healthcare team.
Bag actuator: It should be possible to generate at least 50cmH2O of pressure relatively quickly, but with very fine control of the pressure and little momentum. The ventilator has to be able to stop itself instantly once either a certain pressure threshold or a specific volume is delivered. It should be able to deliver its maximal breath capacity of at least 900mL in as little as 0.4 seconds.
Bag actuator types:
- Strap: A strap holding the bag against a stationary surface tightens and releases, pulled by being wrapped around a cylinder by a stepper motor.
- Linear: a piston drives a plate against the bag on a stationary surface
- Clamp: one arm pivots to squeeze the bag against a stationary surface, or two arms pinch together around the bag
Fig: strap compression: a strap (red) passing over the bag-valve (blue) is pulled by a stepper motor that turns a drum (small black circle).
Design: Completely Design & Simulated in DASSAULT SYSTEMES 3DEXPERIENCE Platform.
Design phase with CATIA :
Assembly phase with CATIA and ENOVIA
System:
Prototyping Phase and demonstration :
Electronics:
Smart circuit with LCD Display Screen with knob/button interface
Speaker for alarms
Software:
Ventilators have different modes, the most basic of which are:
- Volume Control (aka Assist Control): ventilator delivers a breath of a fixed volume. Does not take pressure into consideration.
- Pressure Control: ventilator delivers a breath until a certain pressure is reached and stops, does not take delivered volume into consideration.
They also have different features:
- Triggered breaths: when the vent detects the beginning of inhalation, it delivers a breath
- Detected by beginning of flow towards the patient when no breath is being delivered (caused by patient inhaling through the circuit
- There must also be a back-up rate, where the ventilator takes over if the patient is breathing too slowly or not at all (determined by the amount of time between breaths)
- Alarms for
- Pressure too high (for volume control modes)
- Volume delivered too low (for pressure control modes, requires setting a goal minimum volume)
- Power failure
- Tube disconnect (no resistance or change in pressure when giving a breath)
- Nice to have: alarm for breath stacking (incomplete exhalation causing air trapping from multiple breaths)
- Inspiratory hold: gives a breath and prevents exhalation temporarily while a button is pressed
- Measurement and display (ideally numerically and with a graph) of pressure, tidal (breath) volume, plateau pressure (where the pressure settles during an inspiratory hold)
- Control overMinimum respiratory rate
- Pressure
- Tidal volume
- Inspiratory time
- Mode
- PEEP
