Ventilator for Covid-19
Today we hear a lot about ventilators as treatment to Covid-19 and respiratory diseases. What are the ventilators? Ventilators force air and oxygen into the lungs. Not only for Covid-19, ventilation is used in many others situations. For instance, we perform as first aid act soon we find someone is not breathing. Ventilation is also given if someone suffers acute asthma, cardiac arrest, chronic lung disease, even acute heart failure. Ventilator is not the only way to pump air into lungs. Mouth resuscitation has been performed since the 17th century.
Bag Valve Mask for temporary resuscitation
Later on, bag valve mask was invented which pumps air with clinicians squeezing bag in a controlled manner. Where Covid-19 is different, is that in the past clinicians have only ever be required to squeeze ball when patient is taken to intensive care unit. On contrary, Covid-19 requires much longer ventilation. Covid-19 Patient might need mechanical ventilation for several weeks or it might lead to months. If you have seen my other video on vaccine and human body systems, you would have remembered that Covid-19 causes inflammation to air sacs also called alveoli. Inflammation then prevent oxygen from reaching the lungs. So we could use ventilators to force oxygen into lungs until immune system has defeated the virus and let alveoli to self-heal naturally.
Ventilator Challenge UK and engineering specification
20- Recently, government made a plea to private manufacturers to produce ventilators. As a matter of fact, a competition was launched named VentilatorChallengeUK which is a consortium between prominent manufacturers with the likes of RollsRoyce, Mclaren, and Dyson.
How difficult it is to make the ventilators? Can and shall me and you make one? Of course, it is a call to duty! It is a call to save innocent citizens of community. And I shall accept the challenge with courage and offer my utmost dedication to contribute and build it to perfection.
Let’s have a look at the requirement for ventilator in detail.
Designing Ventilator, Adjustable Settings:
We needs some adjustable settings:
- Tidal Volume: 100-800 mL
- Respiratory rate : 10 – 40 breaths/min
- I:E ratio : 2:1 to 1:4
- Maximum Pressure : 100 – 600 mm H20
- Patient triggered Breathing : On/Off
- Alarm disconnect PIP : 0 to 200 mmH2O
- Alarm Pressure : 100 to 700 mmH20
- Alarm Low Minute Volume : 0 to 30000 mL
- Alarm High Minute Volume: 0 to 30000 mL
Designing Ventilator, Indications and Alarms
Peak Inspiratory Pressure PIP
Positive End Expiratory Pressure PEEP
We need some alarms i.e. Disconnect ( PIP below threshold for 3 breaths, minute volume below/above threshold, Pressure threshold exceeded).
Innovating Bag Valve Mask
A curious mind would question? Could we simply automate and squeeze bag at set frequency repeatedly using a motorised robotic arm? As a matter of fact, many attempts that have been made around the world in response to Covid-19 pandemic are based on BVM, bag valve mask. I do not see bag valve mask as the finest approach. There are numerous reasons. For instance, mechanical ventilation via BVM could lead to barotrauma.
Breathing and diaphragm activity
When we breath, diaphragm and intercostal muscles contract. Such contraction results in increase in thoracic cavity volume where lungs reside. Bernoulli principle, increase in volume results decrease in pressure. Negative pressure within body results in outside air moving into lungs to equalise pressure. Process is opposite during exhalation when slight pressure above atmosphere drives CO2 outside the body.
Our lungs do not inflate like a balloon. It is negative pressure that results in inhalation. If ventilation is not controlled, it could work against the action of diaphragm and intercostal muscles. It could result in expanding lungs when diaphragm is relaxing ( means pushing towards the chest). Consequently, it could end up putting more pressure on the lungs air sacs alveoli. It could be further damaging the conditions of Covid-19 patients.
Pressure and Flow Control
Design must regulate both volume and pressure of air entering into the body. A motorised squeezing of balloon would not achieve this!
Sensors could be used to detect drop in airway pressure during the expansion of thoracic cavity. The alternative is to detect electrical activity of diaphragm to detect diaphragm contraction during inhalation. These are possible ways to detect when patient is attempting to breath. Another issue with bag squeezer is lung compliance of covid-19 patient. Covid-19 patients have low lung compliance. A low compliance lung is like a stiff thick sticky ballon which might require extra pressure/flow at beginning of inhalation. Accordingly, covid-19 patients are required to be kept at PEEP pressure to prevent the lungs from collapsing completely during exhalation.
Other issues with bag squeezer are: more moving parts, motors, gear train, robotic arms. All of these means more cost to manufacture, bigger heavier device and more maintenance issues. Not to mention further engineering challenge to calibrate squeeze against required flow and pressure. We need compact, low-cost device that could be easily manufactured and readily available if we are to win the battle against future pandemics. 20s- In the future videos, I would walk through the design of a compact, low cost ventilator that could be easily produced at a large scale to defeat the virus and save innocent lives, communities and economies that are on the verge to fall in to recession.
Medical Device Legislations and certifications
Medical devices in UK during Brexit Transition are still governed by EU legislation. Accordingly, devices need to be CE marked which might require vigorous quality assurance tests.
Governing body within UK is Medicine and Healthcare products Regulation Authority abbreviated as MHRA. Device manufacturers need approval and license to manufacture from MHRA. Process could be done faster by acquiring certification and testing from BSI, British Standards Institute. Medical devices are categorised into Class 1,2,3 based on associated risk and its application be it implantable, invasive and so on. Ventilators are classified as Class 2 devices and require clinical tests prior made available commercially to treat patients. .
Ventilator Challenge Consortium
Perhaps the route to produce faster ventilator could be utilising production lines from private manufacturers as subcontractor for existing medical device manufacturers who have the appropriate licenses. The other difficulty is to source parts as individual parts that make up ventilator comes from all over the world. Supply chain, logistics involved might not be favourable to produce ventilators at the right we require. However, it is still going to be a worthwhile engineering practice for us to go through the technical challenge involved in designing the ventilator that could potentially save numerous lives.
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