“High Energy” Ventilator...Battery Manage ment System DC/DC 24/24 24V BATTERY 230VAC 24VDC Ground Remote ON/OFF 18 - 26VDC BAT Monitoring 230VAC 24VDC 5A UPS autonomy >45 minutes

“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.


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.


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


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.


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


https://arxiv.org/pdf/2004.00534.pdf

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


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.


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.


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


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


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)


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.


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 !


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.


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.


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.


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.


Native GUI (on touch screen)

Multiple language capability (localisation)

Robust data entry/modification procedure.


Web GUI.

Allows control/monitoring

from a remote nursing

station.


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


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)


Compressed air with turbine or

compressor. (EPFL)


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.


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.


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


Variable pressure risetime.

Variable risetime


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


Performance benchmarking with lung

simulator


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.


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.


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.

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/879382/RMVS001_v4.pdf

https://apps.who.int/iris/handle/10665/331792

https://www.aami.org/docs/default-source/standardslibrary/200410_cr501-2020_rev1-2.pdf?sfvrsn=699e62b7_2

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).


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.


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”:


https://hev.web.cern.ch/

https://indico.cern.ch/event/916953/

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 !


Documents

“High Energy” Ventilator...Battery Manage ment System DC/DC 24/24 24V BATTERY 230VAC 24VDC Ground Remote ON/OFF 18 - 26VDC BAT Monitoring 230VAC 24VDC 5A UPS autonomy >45 minutes