The use of sophisticated medical devices
now more than ever helps medical practitioners
diagnose with ease and accuracy. Their level
of dependency on devices, however, has raised
concerns about ensuring the safety and quality
of the devices. Notably, medical devices rely
heavily on third-party and legacy software,
often referred to as software of unknown pedi-
gree (SOUP). This SOUP forms the basis of
new developments, which may now be subject
to new medical device requirements or modern
coding standards imposed by government,
client demands or simply a policy of continuous
improvement within the developer organiza-
tion. The need to leverage the value of SOUP,
while meeting new standards and further de-
veloping functionality, presents its own set of
unique challenges.
An analysis of 3140 medical device recalls con-
ducted between 1992 and 1998 by FDA reveals
that 242 of them (7.7%) are attributable to
software failures. Of the software recalls, 192
(or 79%) were caused by software defects in-
troduced after software upgrades. The high
percentage of errors introduced during product
upgrade has caused government agencies for
medical devices to focus not only on develop-
ment, but on subsequent maintenance and
the impact of software change on the existing
system. Because of this, many companies are
changing their approach to improve their soft-
ware processes as well as to adopt IEC 62304,
a standard for design of medical products re-
cently endorsed by the European Union and
the United States. IEC 62304 introduces a risk-
based compliance structure - Class A through
C where the failure of Class C software could
result in death or serious injury - that ensures
medical applications comply with the standards
suitable for their risk assessment.
IEC 62304 focuses on the software development
process, defining the majority of the software
development and verification activities. This
process includes activities like software devel-
opment planning, requirement analysis, archi-
tectural design, software design, unit imple-
mentation and verification, software integration
and integration testing, system testing and fi-
nally software release. This standard not only
outlines requirements for each stage of the de-
velopment lifecycle, but also takes care of the
maintenance process, the impact of software
change to the existing system, and the risk in-
volved in implementing the software change.
IEC 62304 also discusses in detail the effect of
the SOUP items from planning, requirement
analysis, architectural design, maintenance,
through to the management phases. The IEC
62304 standard provides a framework of soft-
ware development lifecycle processes with ac-
tivities and tasks necessary for the safe design
and maintenance of medical device software.
This standard basically identifies five main
processes. The software development process
defines the majority of the software develop-
ment and verification activities. The software
maintenance process oversees the released
product, monitoring for future problems in
order to correct them and to ensure that cor-
rections will not cause a hazard or a risk to the
existing system. The software risk management
process identifies the software items that con-
tribute to hazardous situations. Their causes
are identified, documented, and appropriate
risk control measures are implemented and
verified. The software configuration manage-
ment process identifies and documents the
history of changes made to the software system.
Finally the software problem resolution process
analyzes and resolves any problems, whatever
their nature or source, discovered during the
development, maintenance or other processes.
SOUP software that can be reused in the de-
velopment of new devices has become prevalent
since medical devices now tend to be built on
general-purpose embedded hardware, such as
an operating system, device drivers for USB,
Ethernet, or graphics, file systems, network
stacks, etc. The use of SOUP in medical devices
has its advantage in that the manufacturer can
concentrate on the application software. How-
ever, since the applications need to run device-
specific functions, SOUP in medical devices
Certifying medical devices: easing
IEC 62304 compliance for developers
S
OFTWARE
D
EVELOPMENT
By Anil Kumar,
LDRA
This article focuses on
how to bring the so-called
SOUP legacy (software
of unknown pedigree) and
third-party products into
compliance with IEC 62304,
and how to upgrade SOUP
without introducing errors
that adversely affect the
safety of medical devices.
October 2013
20
