Transcript Medical Device Electrical safety - Safety

Maybe everything you wanted to know but were afraid
to ask.
Patrick Maw
Medical Physics & Bioengineering
UCLH NHS Foundation Trust
June 2014
Outline
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What does a Medical Device Look Like
Regulations
Standards
Effect of Electricity on the body
Electrical Hazards from Medical Equipment
Construction of Medical Equipment
Medical Equipment Safety Testing and Inspection
Other equipment in the patient environment
Medical Electrical Systems
Networked Medical Devices
Questions?????
What does a Medical Device look
like?
Regulations
 Medical Device Directives 93/42/EEC
 Any instrument, apparatus, appliance, software, material or other article,
whether used alone or in combination, together with any accessories, including
the software intended by its manufacturer to be used specifically for diagnostic
and/or therapeutic purposes and necessary for its proper application, intended
by the manufacturer to be used for human beings for the purpose of:
 Diagnosis, prevention, monitoring, treatment, or alleviation of disease
 Diagnosis, monitoring, treatment, alleviation of, or compensation for an injury
or handicap
 Investigation, replacement, or modification of the anatomy or of a
physiological process
 Control of conception
 This includes devices that do not achieve their principal intended action in or
on the human body by pharmacological, immunological, or metabolic
means—but may be assisted in their function by such means.
Regulations
 Medicines and Healthcare products Regulatory
Agency (MHRA) – Competent Authority for UK
 Application through law of the MDD
 Recent revisions now recognise software as a Medical
Device.
Standards
 Main series of standards – IEC 60601 – 3rd edition
 IEC 60601-1-1 General requirements for basic safety
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and essential performance.
IEC 60601-1-2-x Particular requirements for CT, MR,
Defibrillators …………
ISO 13485 – Quality Management in Medical Device
design and manufacture
IEC 61010 – Laboratory equipment. Formerly covered
by ESCHLE.
ISO 14971 – Risk management for medical device
safety
Effect of Electricity on the
body
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Neuro-Muscular
Dependent on current density, frequency, duration and the
particular neuro-muscular system.
For 50Hz current passing between the hands the following
ascending scale of effects are:
1 mA – Perception
10 mA – Can’t let go
100 mA – Severe pain and interference to the Heart and
chest function
1 A – Sustained heart contraction
However effects start to diminish at frequencies above
100KHz
Effect of Electricity on the
body
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Tissue Heating
Exceptionally high currents passing through the body
cause tissue heating.
Extent of heating depends on the local current and
resistance because of:
Power = Voltage (V) X Current (I) but
Voltage = Resistance (R) X Current (I) so
Power = R x I x I or R x I 2
Cutting, Coagulation and Physiotherapy Ultrasound
are controlled uses of this effect.
Effect of Electricity on the
body
Electrolysis
 Direct or very low frequency currents (Less than
0.1Hz) are conducted as IONIC currents
 This can cause ulcerations of the skin that are slow to
heal
 Effect used deliberately in hair removal
Electrical Hazards from
Medical Equipment
 UK mains supply 230V 50Hz
 Main hazard is that the line connection is seeking a route
to earth by any means
 Main protection against electrocution is dry skin and the
ability to pull away. Hospital patients have both of these
removed due to low impedance skin connections and
sedatives
 Protective Earthing (PE) is a common method to reduce
electrical hazards by providing a low resistance path in the
case of a fault. Double insulated equipment does not
require a safety earth because no mains parts are accessible.
 Leakage currents are present even when equipment is
operating normally. Reduced by use of a PE.
Construction of Medical Equipment
 There are 3 main classifications for Medical
Equipment to indicate protection against Electric
Shock
 Class 1 equipment relies on a protective earth.
 Class 2 equipment relies on double layers of
insulation.
 Class 3 equipment is internally powered below the
Safety Extra Low (SELV) level of 50 Vac
Construction of Medical Equipment
 This is further subdivided by the degree of protection
for patient applied parts:
 Type B equipment patient part may have a low
impedance path to earth
 Type BF equipment has a floating type patient part
that has a high impedance path to earth using devices
such as a transformer.
 Type CF equipment is similar but has much lower
allowed levels of leakage that are deemed safe even
when connected directly to the heart.
Construction of Medical Equipment
Leakage Current
(mA)
Type B
NC
Type BF
Type CF
SFC
NC
SFC
NC
SFC
1
Earth
0.5
1
0.5
1
0.5
Enclosure
0.1
0.5
0.1
0.5
0.1
0.5
Patient
0.1
0.5
0.1
0.5
0.01
0.05
NC = Normal
Condition
SFC = Single
Fault Condition
Medical Equipment Safety Testing
and Inspection
 MHRA Device Bulletin 2006 (05) November 2006
Managing Medical Devices covers:
 Systems of management for Medical Equipment
 Acquisition of Medical Equipment
 Maintenance and repair
 Decontamination
 Removal from service
Medical Equipment Safety Testing
and Inspection
 All re-useable Medical Equipment is subject to regular
preventative maintenance to comply with
manufacturer guidelines as a minimum
 This can be carried out by either the local hospital
team or manufacturers.
 Appropriate training should be given to the local team.
The availability of this is checked during procurement
by use of a Pre Purchase Questionnaire (PPQ) during
the procurement.
Medical Equipment Safety Testing
and Inspection
 Custom made safety testers are available that will carry
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out the required measurements for:
Earth Continuity
Insulation Resistance
Earth Leakage
Enclosure Leakage
Patient Leakage
 However these testers are only suitable for non PC
based Medical Equipment
Medical Equipment Safety Testing
and Inspection
 Equipment such as CT, MR, Ultrasound are now based
on Windows Operating Systems – 2000, XP, 7 ?
 All Safety Testers interrupt the mains supply to give a
Single Fault Condition (SFC) which can damage a PC
hard disk and therefore the Medical Equipment.
Requiring the system to be re-installed.
 Solution is to make sure the Medical Equipment is
powered down between tests and most testers have a
manual mode.
 New generation of testers that will correctly handle PC
based systems are available.
Medical Equipment Safety Testing
and Inspection
 Testers are only suitable for equipment with a mains
plug up to a maximum rating for current.
Unfortunately one of these
 Can’t test
Medical Equipment Safety Testing
and Inspection
 One of these:
Finding Medical Devices for
Maintenance and Testing
 How do we find Medical Devices?
 Wander around and hope for the best?
 Don’t carry out maintenance?
 NO – We use technology.
 Systems that use WI-FI to track a tag attached to
Medical Devices.
 This can give a real-time display of the location of
tagged devices overlaid onto building floor plans.
Other equipment in the patient
environment
 The patient environment is defined:
Other equipment in the patient
environment
 All equipment within this area must comply with the
requirements for safety of Medical Equipment.
 However not all equipment is built to comply with IEC
60601-1
 An example is a standard PC used for data gathering
from Medical Equipment.
 Would this be allowed?
 Yes providing that adequate precautions are taken to
ensure that the PC is made to meet the safety
standards.
Other equipment in the patient
environment
 How is this done?
 1) Connect the PC mains supply via a Medical grade
isolation transformer.
 If the PC is networked then a Medical Grade LAN
isolator is required as well. All this has the effect of
reducing the Earth, Enclosure and Patient leakage to
safe levels as defined in IEC60601-1.
Other equipment in the patient
environment
 2) Medical grade isolators on the signal connections. A
whole range of these are now available:
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RS232 – Serial
Video
Ethernet
Other equipment in the patient
environment
 3) Use a Medical Grade PC. These are now widely
available from a number of suppliers
Medical Electrical Systems
 What is a Medical Electrical System (MES)
 It is a collection of equipment both Medical and non-
Medical that interconnect via signal connections.
Medical Electrical Systems
 It is not different Medical Electrical Equipment
connected at the same time to a Patient but not to
each other.
Medical Electrical Systems
 What are the potential dangers of equipment
connected in this way?
 Even when it is all Medical Electrical Equipment there
is a possibility that dangerous levels of Enclosure
Leakage may be present.
 It is common to connect all the parts using a Multiple
Power Socket Outlet (MPSO). If precautions are not
taken other equipment can be connected into this
MPSO and compromise safety.
Medical Electrical Systems
 How do we ensure that the system is safe:
 1) All parts of the system must pass a full Medical
Electrical Safety Test.
 2) Measure the combined Earth Leakage under
Normal Conditions. Value not to exceed 0.5mA
 3) Break the Protective Earth to each element of the
system one at a time and measure Enclosure Leakage
on each part of the system. Value not to exceed 0.5mA
 4) Measure Earth resistance for each system element
back to the MPSO plug. Value not to exceed 0.4Ω
Medical Electrical Systems
 NOTE:
 Earth Resistance – Single Item under Normal
Conditions is 0.1Ω, MES is 0.4Ω
 Earth Leakage – Single Item under Normal Conditions
is 0.5mA, MES is 0.5mA
 MPSO must either be covered to prevent the
connection of unwanted items without the aid of a
tool or
 Use a non-standard connector.
Networked Medical Devices
 Requirement for an Electronic Patient Record (EPR).
 What we had:
Networked Medical Devices
 However there are:
 Admission, Discharge and Transfer (ADT) systems.
 Picture Archive and Communication System (PACS)
for Medical Images.
 Clinical Information Systems (CIS) for Patient Charts.
 Variety of Archiving systems.
 All of these require Medical Devices to be networked.
Networked Medical Devices
 As previously mentioned current Medical Devices are
based on Windows Operating Systems.
 More importantly older Windows OS’s – 2000, XP.
 Due to the extensive validation of a Medical Device
patches and Security updates cannot be installed in
real time.
 In the majority of cases Anti-Virus is not present and
cannot be installed.
 This therefore presents a real security issue.
Networked Medical Devices
 How do we deal with this???
 Cross our fingers and hope we don’t have a problem?
 Remove all devices from the network and go back to
paper\film records?
 NO – We implement measures to mitigate the risk.
 Internal Firewalls to segregate Medical Devices.
Networked Medical Devices
 80001 series of standards are now available to guide on
the division of responsibilities.
 Medical-IT-Network – Defined as:
 A network that includes at least one Medical Device.
 Medical-IT-Network Risk Manager.
 Recognises that involvement is required by the local
Medical Device experts such as Medical Physics.
 Not just an IT problem.
Networked Medical Devices
 Advantages;
 Better record keeping through central archiving.
 Greater Patient Safety through central admin of
critical systems such as Drug Libraries for Infusion
devices.
 Disadvantages;
 If security is not handled effectively major parts of the
Hospital can close such as A&E. Not good for patients.
Questions??????