Transcript Chapter 20: Product Issues

Chapter 21: Product
Issues
Design of Biomedical Devices and Systems
By:
Paul H. King
Richard C. Fries
Product Safety & Legal Issues
 Risk


Assessment
What failure could cause harm to the patient
or user?
What misuse of the device could cause harm?
 Liability


Assessment
Have all possible failure modes been explored
and designed out?
Have all possible misuse situations been
addressed?
Safety
 Freedom
from accidents or losses
 A function of the situation in which it is
measured

A
Drinking water & kidney failure
measure of the degree of freedom from
risk in any environment
Safety
– unwanted or unexpected
release of energy (old definition, see
history of gunpowder, TNT manufacture,
etc.)
 Mishap – unplanned event or series of
events that result in death, injury,
occupational illness, damage to or loss of
equipment or property, or environmental
harm
 Accident
Mishap
 Multiple
factors that flow in series until the
system is out of control and a loss is
produced


Anticipation of simpler problems needed!
Opportunities for interruption –study!
How Do Engineers Deal With
Safety Problems?
 Operational


or Industrial Safety
Examination during operational life
Correcting unacceptable hazards
Examine
Accidents
 Goal:
Determine
Causes
Correct
design an acceptable safety level
into the system before actual production or
operation
Safety and Reliability
– only concerns itself with failures
that introduce hazards
 Reliability – probability of failure of a
device to meet its requirements
 Safety
Safe System


One in which damage to persons or property doesn’t
happen often or, when it does, the damage is minor
Small damage potential



Large damage potential



Able to occur more often
Still considered Safe
Chance for mishap small
System that fails all the time can still be safe
System can be up and running all the time and
consistently put people at risk

Reliable system, but not Safe
Example: Pacemaker
 Pacemaker
that paces at 110 beats per
minute continuously no matter what is very
RELIABLE
 If patient is in cardiac failure, high pacing
rate is medically inappropriate. UNSAFE
 Reliable but Unsafe device
MTTF & MTBF
 Mathematical
laws of probability used to
estimate reliability
 Published values for reliability measures:


Mean Time To Failure
Mean Time Between Failure
Legal Aspects of Safety
3



Most Common Theories of Liability:
Negligence
Strict liability
Breach of warranty
Negligence

One should pay for injuries that he causes when
acting below the standard of care of a
reasonable, prudent person participating in the
activity of the action in question
 People have the right to be protected from
unreasonable risks of harm
 A manufacturer that does not exercise
reasonable care or fails to meet a reasonable
standard of care in the manufacture, handling, or
distribution of a product may be liable for any
damages caused.
Strict Liability

Focus on product
 One who sells any product in a defective
condition unreasonably dangerous to the user or
consumer or to his property is subject to liability
for physical harm thereby caused to the ultimate
user or consumer or to his property if the seller
is engaged in the business of selling such a
product, and it is expected to and does reach the
user or consumer without substantial change to
the condition in which it is sold.
 Risk/benefit analysis
Breach of Warranty
3



Types
Breach of implied warranty of merchantability
Breach of the implied warranty of fitness for a
particular purpose
Breach of an express warranty
System Safety
– designed to fail into a safe and
harmless state
 Enter safe states by terminating or
preventing hazardous conditions (lockouts
or shutdown systems)
 Should be able to work despite failure of
other functions
 Fail-safe
Hardware Safety
 Techniques
for reducing failure of
component:



Component derating
Safety margin
Load protection
Software Safety
 Safety
is a concern when used to control
potentially unsafe systems
 Safety needs to be considered in the
design of software packages, especially
when considering the “crash” of a system
 Software failures are a major source of
recalls…
Verification & Validation of Safety
of Safety –fault cannot occure or if a
fault occurs it is not unsafe…
 Verification – capture the semantics of the
hardware, software code, and the system
behavior
 Fault-tree analysis
 Proof
Effective Safety Program
 Implementation
of internal hazard analysis
procedures, a firm grasp of regulatory and
other standards, and an awareness of the
current industry practice regarding safety
controls
 Figure 21-1 Safety Analysis Checklist
Accident Reconstruction &
Forensics
 Biomedical
Engineers may be used to
analyze accidents
 Analysis of Medical Device accidents
 Discussion on biomechanics and accident
investigation
Medical Device Accidents
 Process
for a medical device accident
investigation: accident/contact/data
collection(MAUDE, DHF,
other)/hypothesis/report/court or settle
 Examples follow:
Medical Cases:
 Enteral
feeding tube complication
 Pressure limited respiration system
 IM Nail accident
 Penile implant
 Blood oxygenator
 Failure to monitor
 Failure to perform (car/ventilator/child)
Biomechanics & Traffic Accident
Investigations




Data Collection
 National Highway Transportation Safety
Administration (NHTSA)
Injury Estimation
 Abbreviated Injury Scale (AIS)
Impact Analyses
 Accident report, crush patterns, etc to estimate
probable outcome
Generally collaborate with Orthopedics…
Safety or lawsuit!