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“High Energy” VentilatorJan Buytaert
On behalf of all our HEV collaborators !
5/19/2020HEV project.( CERN ESE seminar)2
HEV collaboration:
Members from University of Liverpool (Liverpool), EPFL (Lausanne), UFRJ (Rio de Janiero), IGFAE/USC (Santiago de Compostela), Nikhef (Amsterdam), University of Manchester (Manchester), University of Nis (Serbia), CUT (Cracow), University of Applied Sciences (Offenberg). Riga Technical University (Latvia).See https://arxiv.org/pdf/2004.00534.pdf
CERN groups:
EP-DT (Detector Technologies) group (mechanical design, pneumatic components)
EP-ESE (Electronics Systems) group, ( electronics design and integration)
EP-LBD,LBC,LBO (LHCb experiment groups)
HSE (Safety at CERN) unit (medical contacts, working practices at CERN during Covid-19 era, working relationship with HUG, conformity with applicable legislation and health and safety requirements)
BE-CO, BE-ICS, webpage, open source consultation, functional safety analysis of control systems
DG-LS, IPT-KT, ongoing consultation on deployment, knowledge transfer and legal aspects.
5/19/2020HEV project.( CERN ESE seminar)3
Advice & guidance from medical
experts.
Many thanks to
Lise Piquilloud, Patrick Schoettker, CHUV, Lausanne
Philipp Rostalski and Georg Mannel, Luebeck University
Laurence Vignaux; Hôpital de La Tour, Geneve
Josef X. Brunner: Neosim, and ventilator design
Gordon Flynn and David Reiner; Canberra Hospital, Canberra
Hamish Woonton: Dandenong Hospital, Dandenong
Bruce Dowd, Prince of Wales Hospital, NSW
Carl Roosens, University Hospital Ghent
M. de Carvalho, N. Dousse, M. Saucet, HUG Geneve
Special thanks to the HUG who have loaned us equipment, via the special
collaborative agreement between CERN and HUG, and to the
Pneumology and Cardio-Respiratory services and NIC centre of Hôpital de
La Tour.
5/19/2020HEV project.( CERN ESE seminar)4
outline
The goal of the HEV project.
The initial demonstrator phase
The prototyping phase.
System overview.
Technical aspects
Mechanical & pneumatics
Electrical system & powering
Embedded control,software development & GUI’s
O2 mixing & measurement
Specifics of ventilation
Benchmarking performance
Alarms
Risk analysis & international regulations
Next steps
Summary
5/19/2020HEV project.( CERN ESE seminar)5
The HEV project goals
Following the outbreak of the pandemic, there was/is a severe shortage of ventilators for intensive-care-unit in hospitals.
The functionality is aimed at the treatment of the vast majority of COVID-19 cases, following recommendations issued by MHRA, AAMI, WHO.
The availability of HEV as a ventilator option could free up the very high-end machines for the most intensive cases.
HEV is a fully specified ventilator system suitable for hospital use,
both in and out of intensive care units (ICU),
for both intubated and mask/non-invasive cases.
The pressure controlled modes are PC-A/C, PC-A/C-PRVC, PSV, CPAP.
The system is flexible and could provide volume control modes.
The user interface is ergonomically, intuitive and clear. The layout is inspired by best practice in use of commercial ventilators.
It is low cost, high quality, robust and simple to construct based on readily commercially available components.
Suitable for wide range of geographical deployment; local implementation and part choices depending on local requirements.
5/19/2020HEV project.( CERN ESE seminar)6
How it started
23 March: we learn about a development “Brompton
AMVENT” for a “Rapid Manufactured Ventilator” following
MHRA (Medicines and Healthcare products Regulatory
agency) specifications. Project is stopped a little bit later.
25 March: we submit a proposal to CERN management and
is accepted by CERN against COVID19.
27 March: start assembling a “demonstrator” at CERN with available components.
28 March: a first breathing cycle is registered
1 April : submit an arxiv note
https://arxiv.org/pdf/2004.00534.pdf
5/19/2020HEV project.( CERN ESE seminar)7
The first proposal.
An air reservoir was initially foreseen for ‘decoupling’ of pressure regulator.
Roberto Guida (CERN EP/DT gas group) proposed a modification (addition of an input valve) adding cautiously : “We should have all components. It sounds too easy to be true. I’m afraid we are missing something on how this machine works.”
This additional valve closes the buffer and splits the ventilator in 2 almost independently functioning parts: “filling” and “draining”
Original proposal
Modified proposal
added
5/19/2020HEV project.( CERN ESE seminar)8
Why a demonstrator ?
A buffer based ventilator is not ‘mainstream’ or classical.
Prove and find possible limitations ?
To optimise the various valves in the system and regulator: each has very
different requirements;
zero back pressure, response time, Kv (flow resistance)…(We have tried every
valve that we had available, pinch, even vacuum valve !)
Understand the pressures, flows, transients and time constants of the system.
Start the design of a LabView based control software.
5/19/2020HEV project.( CERN ESE seminar)9
Phase 2: rapid prototyping
4 to 17 April with the aim
To integrate all the final functionality.
and produce 3 prototypes asap to allow parallel development of pneumatics, embedded system and performance testing.
Components chosen for immediate availability , not for cost or medical grade.
Mechanical size and weight and ergonomics are not optimised.
Organise in subgroups, each at least 5 members
Pneumatics & mechanics
Electronics & powering
Embedded software & User interface
Safety and regulatory aspects & documentation.
Analysis of measurements with lung simulator.
5/19/2020HEV project.( CERN ESE seminar)10
HEV block diagram
Buffer
Pressure relief valve
inhale
Controller/monitor
valve_O2_in
P_Supply_AirP_Regulated_Air
P_inhale
P_bufferT_buffer
Pressure relief valve
buffer
P_patient dP_Patient
Pressure Regulator
O2
P_Regulated_O2P_Supply_O2
T_ambientP_ambient
Green box is controlled
Orange box is manual
valve_Air_in
CV1
CV2
CV3 - ValveInhale
Guarantee
CV4
CV5
valve_inhale
PowerSource
Mains
Battery
Humidifier
Heat and Moisture
Exchanger (HME)
Hepa Filter
Water trap
valve_exhale
Positive End
Expiratory
Pressure Valve
Flow meter*
Pressure Regulator
Air
valve_purge
*Under discussion
Air
O2
5/19/2020HEV project.( CERN ESE seminar)11
Ventilator State Chart.
Every 10ms :
All pressures are read.
All valves states are updated
The state changes are
time-driven
or on conditions of pressure
change.
The states define the actions on
the valves.
Implemented in software in
ESP32 microcontroller.
idle
Calibration
Buffer Prefill
Buffer Fill
Buffer Loaded
Buffer Pre-Inhale
Inhale
Pause
Exhale-Fill
Exhale
Stop
Buffer Flush
Buffer to Purge
5/19/2020HEV project.( CERN ESE seminar)12
Advantages of the buffer concept.
Step-down pressure buffer between supply and patient introduces safety and robustness
against variable gas supply.
Step-down pressure buffer makes precise pressure control more readily accessible
Buffer allows a natural way to mix air and O2, so no need for an additional oxygen mixer
Measuring O2 concentration on ‘static’ gas volume vs measurement on a gas stream does
not require fast reaction time of meter (more precise method)
From a pneumatic perspective, separating the fill and exhale cycle into two separate
circuits makes the design, control and component selection easier and allows less
expensive components to be selected.
Thermal control of the gas in the buffer is a possibility e.g. for extreme environments
The delivered tidal volume can be
calculated from the pressure drops in the
buffer. (this is a precious monitoring cross
check in addition to the standard tidal
volume measurement (additional safety)
5/19/2020HEV project.( CERN ESE seminar)13
The prototypes
5/19/202014
10L buffer
Air tubes
to patient
Touch
screen
Alarm
indicator
PCB with Embedded
Processors & I/O to
valves and sensors
220VAC/DC &
24V battery UPS
Cooling fan &
input filter
Back compartment (electrical) Front compartment (pneumatic)HEV project.( CERN ESE seminar)
Mechanics & Pneumatics
Dimensions 50x40x100 (cm). Small
footprint.
Cabinet on wheels. Can easily be
moved by 1 person. Very stable.
2 separate compartments (back &
front): pneumatics and electronics.
(Explosion risk if O2 leak).
Doors for access (cleaning).
Air tubes connect through standard
bulkhead thread connector on the
outside. Easy replaceable to match
hospital connection standards around
the world.
5/19/2020HEV project.( CERN ESE seminar)15
Pneumatic design.
5/19/202016
Exhaust
Exhale
branchInhale
branch
Purge valve
Pressure relief
Oxygen Inlet Air Inlet
Oxygen inputValve
Air inputValve
Inhale Valve
Exhale Valve
HEV project.( CERN ESE seminar)
Electrical Functional diagram
17/2
3 ESP32
Regulated 24VDC
DCDC24VDC/5VDC
TRACO THM20
VALVE AIR IN
VALVE SPARE 2
VALVE SPARE 3
VALVESPOWERCONTROL
2X L298N
VALVE INHALE
VALVE EXHALE
VALVE PURGE
VALVE O2 IN
VALVE SPARE 1
-VENTILATOR CONTROL.-SENSORMONITORINGAND VALVE CONTROL
P_AIR_SUPPLY
P_AIR_REGULATED
P_BUFFER
P_INHALEP_PATIENTP_O2_SUPPLY
P_O2_REGULATEDP_DIFF
PRESSURESENSORS
TEMP.SENSOR P_TEMP
RPI_TEMP I2CVALVES VOLTAGE AND CURRENT MONITORING
I2C
BATTERYMONITORING
BATOKALARM
RDY2BUFBAT85
USER INTERFACE
RASPBERRY PI 4B
USB-C
TOUCH SCREENWITH EMBEDDEDBATTERY
DC PS
VISUAL AND AUDIOStatus indicators
3X LEDS + 1 BUZZER
FAN
4X INA226
5/19/2020HEV project.( CERN ESE seminar)ESP32
Electronics & Electrical design.
Raspberry Pi
ESP32
Valve drivers
Pressure sensor inputs
Power DC/DC
Designed, produced and tested in record time !
5/19/2020HEV project.( CERN ESE seminar)18
Power and UPS supply
Medical versions
according to IEC/EN
60601-1 Breaker can be
changed to be
compatible with
110VAC
C14 PLUG
&FILTER
ON/OFFSWITCH
BREAKER &
Residual Current Device
6A,10mA
AC/DC230/24
Battery Manage
ment System
DC/DC24/24
24V BATTERY
230VAC 230VAC 230VAC 24VDC
Ground
Remote ON/OFF
18 - 26VDC
BAT Monitoring
24VDC 5A230VAC
UPS autonomy >45 minutes.
Additional external battery can be connected.
Medical grade equivalents have already been identified.
5/19/2020HEV project.( CERN ESE seminar)19
Embedded control system.
ESP32 microcontroller:
Handles fully the ventilator operation.
Dual core, single process (no OS).
High availability, low cost.
Raspberry Pi 4:
Handles all communications (touch screen HDMI , wifi & Ethernet) and displays.
Fast reboot.
Ventilator continues to run even if communications go down.
Versatility is built into the design.
5/19/2020HEV project.( CERN ESE seminar)20
Software development
Component failure is considered from the start.
Internal checking/assertions in software.
Developing unit tests.
Following IEC 62304 requirements for medical
software. Experts familiar with this type of
design process are advising us.
Communication protocol following High-level
Data Link Control (ISO/IEC 13239:2002).
Data sending with acknowledge.
Check summing data integrity.
5/19/2020HEV project.( CERN ESE seminar)21
Data server and data contents.
Data server on R-pi interacts with microcontroller ESP32.
Relays reading of process variables (pressures, flow, temperature, valve state)
and derived quantities (minute volume, calculated flow)
Receives commands form UI
Relays alarms in both directions.
Data content.
Data is timestamped and prioritised. Alarms have highest priority. Non-blocking
data, i.e. new data have priority.
Alarms
Subdivided in low , medium & high (coloured light pole on HEV unit).
High priority alarms are displayed first.
5/19/2020HEV project.( CERN ESE seminar)22
Native GUI (on touch screen)
Multiple language capability (localisation)
Robust data entry/modification procedure.
5/19/2020HEV project.( CERN ESE seminar)23
Web GUI.
Allows control/monitoring
from a remote nursing
station.
5/19/2020HEV project.( CERN ESE seminar)24
Mixing of Air & Oxygen
OxygenAirMixed
Adjusted
standard
component
Inh
ale
bra
nc
h
Exh
ale
bra
nc
h
The relative opening
times of the two valves
(O2 & Air) define the
mixing ratio.
regulatorregulator
O2
valve
Air
valve
5/19/2020HEV project.( CERN ESE seminar)25
O2 concentration measurement.
Measured concentration is <5% of
the expected value.
Must improve the time to change to
high O2 concentration. Currently
too slow.
Plan to use O2S-T3 from
sstsensing.(EPFL)
5/19/2020HEV project.( CERN ESE seminar)26
Compressed air with turbine or
compressor. (EPFL)
5/19/2020HEV project.( CERN ESE seminar)27
Basics of respiratory cycle.
Pressurization must have fast rise time(~100ms) for comfort of patient.
Expiratory flow must be 0 at end of exhalation.
A short pause cycle allows estimation of static lung compliance.
PEEP(=positive end of exhalation pressure) must never be lost (lung collapse).
Leaks must be detected and raise alarm.
5/19/2020HEV project.( CERN ESE seminar)28
Supported Ventilation modes
Limited to the essential modes on recommendation from clinicians.
The design is flexible and could rather easily provide volume (flow) control modes.
5/19/2020HEV project.( CERN ESE seminar)29
Pressurization and pressure regulation of
the inhale valve.
Pressure_inhale
P_patient
10L Buffer
Valve_inhale
Valve_exhale
Valve_inhale is a proportional valve(adjustable opening)
A PID algorithm regulates the opening of the valve to maintain P_inhale pressure constant to a target value (+/- 2mbar), independent of flow and buffer pressure.
flow
Buffer pressure
5/19/2020HEV project.( CERN ESE seminar)30
Variable pressure risetime.
Variable risetime
5/19/2020HEV project.( CERN ESE seminar)31
Inspiratory and expiratory trigger.
Paw
time
inspiratory
Trigger (flow)
Expiratory
trigger
Flowtime
sta
rt o
f in
sp
ira
tio
n
sta
rt o
f e
xp
ira
tio
n
100%
x % of peak value
5/19/2020HEV project.( CERN ESE seminar)32
Performance benchmarking with lung
simulator
5/19/2020HEV project.( CERN ESE seminar)33
Example of benchmark plots
(“patient8”)
Scripts have been developed to extract all important quantities (tidal volume, pressure rise time, peak, plateau, inhale trigger response PTP300, …)
These plots show the capabilities of the ventilator for all lung pathologies and breathing efforts.
Will be compared to commercial ventilators.
5/19/2020HEV project.( CERN ESE seminar)34
Alalarm modes and exceptions
23/04/20HEV documentation and regulatory aspects35
• Actions for all ventilator alarms:
• Single buzzer sounds.
• Light goes on in the alarm pole.
• Message appears in reverse text on the screen.
• Depending on error, the audible or visual part can be paused.
• Alarm modes are divided into priorities:
• High (HP) – red light.
• Medium (MP) – flashing orange light.
• Low (LP) – orange light.
• Green light on when no alarms.
• Alarms scroll continuously in order of priority on the main
screen.
• Shown on a dedicated alarm screen in order of priority.
• There is also a remote alarm at the nurses station.
• Alarm logs screen shows the last 8 alarms.
• Technical alarms which don’t affect operation are on an expert screen.
Alarm summary tables
HEV documentation and regulatory aspects36
23/04/20
International Regulations for COVID19
ventilators.
Tables in the HEV
Specification Document
detail the MHRA, WHO
and AAMI requirements
and the corresponding
HEV level of compliance.
5/19/2020HEV project.( CERN ESE seminar)37
1. UK Medicines and Healthcare products Regulatory agency (MHRA) Specification for Rapidly Manufactured Ventilator System (RMVS). Version 4.0, released on 10 April 2020.
2. World Health Organization (WHO) Technical specifications for invasive and non-invasive ventilators for COVID-19: Interim guidance. Version, released on 15 April 2020.
3. US Association for the Advancement of Medical Instrumentation (AAMI), Emergency use ventilator (EUV) design guidance, consensus report. Revision 1.2, released on 8 April 2020.
Failure modes and effects analysis (FMEA)
• In this process we reviewed all the components to identify any
possible failure modes and investigating the consequences and
effects.
• The risk is assessed according to a few criteria (1-4):
• Probability to happen.
• Severity.
• Detectability.
• Mitigating actions: additional measures to reduce the risk to an
acceptable level, resulting from the product of the detectability,
probability and severity.
• Additional safety elements can be used to lower the probability or
increase detectability of the effect in case of failure.HEV documentation and regulatory aspects38
23/04/20
Qualitative
Risk Assessment
1 2 3 4
1 1 2 3 4
2 2 4 6 8
3 3 6 9 12
4 4 8 12 16
6 6 12 18 24
8 8 16 24 32
9 9 18 27 36
12 12 24 36 48
16 16 32 48 64
RPNDetectability
Ris
k Le
vel
[P x
S]
Acceptable risk: no actions need to be
taken.Unacceptable risk:
actions are necessary.
Unacceptable risk:
immediate actions are necessary.
‘Risk Priority Number’
(risk score)
FMEA risk matrix
Failure modes and effects analysis (FMEA)
HEV documentation and regulatory aspects39
23/04/20
Direct hazardous
effects are assessedConsequences of the
failure mode are
listed
Soon: evaluation by clinicians in local
hospitals.
Aim to bring the prototypes to full functionality within a week and to publish
the result of a full suite of measurements with the lung simulator,
corresponding to the regulatory guidelines and the extra tests in addition
which were requested by the clinicians.
Then bring the prototypes for more advanced testing at the hospitals with
which we are working in close collaboration (primarily HUG, CHUV and La
Tour).
5/19/2020HEV project.( CERN ESE seminar)40
Medical certification & production.
CERN is actively contacting and discussing with companies for potential
production. When more clearly defined, then a regulatory prototype will be
built with all medical grade components and more optimised in volume &
ergonomics.
This prototype can be submitted to medical certification process.
5/19/2020HEV project.( CERN ESE seminar)41
Summary
We have designed a pressure controlled ventilator with good performance w.r.t pressure pulse shapes and support for spontaneous breathing.
It is a complete system with user interface on touchscreen and remote web monitoring. It contains a UPS power system and is low power.
All attention has been given to patient comfort and safety.
Additional projects are looking for solution for compressed air supply in absence of wall-distributed medical air in hospital.
It is a high quality, low cost (order of 2-3 kEuros)and robust design, made from readily available components and no single high cost component.
New website https://hev.web.cern.ch/
Seminar tomorrow on CERN against COVID19: https://indico.cern.ch/event/916953/.
Many detailed information available on the “International review of HEV”:
5/19/2020HEV project.( CERN ESE seminar)42
Final thoughts
There is more to a ventilator than just blowing air… Were we naïve when
taking this initiative ? Probably yes, but you need to be an expert to know
that and we were not… but we were surely confident that we are
surrounded by enthusiastic colleagues and collaborators with all the right
skills and knowledge to make a ventilator of high quality at very modest
cost ! And not least, we are very grateful to the medical experts that
believe in our initiative and spent considerable time, effort and dedication
to this project ! Many thanks !
The real success will be when these units will be deployed and help save
lives, possibly even beyond COVID19 pandemic. We believe that we can
try to take on this challenge as well !
5/19/2020HEV project.( CERN ESE seminar)43
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