Evaluation (Validation and Verification) - Medical Device Design: Innovation from Concept to Market - page 215

Table 9.5: A Typical Risk Evaluation Table

S Negligible: 1 Minor: 2 Serious: 3 Critical: 4 Catastrophic: 5

L
Frequent: 5 5 10 15 20 25

Probable: 4 4 8 12 16 20

Occasional: 3 3 6 9 12 15

Remote: 2 2 4 6 8 10

Improbable:1 1 2 3 4 5

Key:
Dark: Unacceptable ( > 10) - Risk must be controlled and RPN reduced.
Gray: Significant ( > 4) - Risk controls to be investigated to reduce RPN.
White: Insignificant ( < 5) - RPN need not be investigated further.

We, once again, refer back to our original PDS. Within this document you will have written
down your acceptance criteria: what the device must do to be acceptable. Quite often the first
stage is to meet the requirements of a specific standard. Whatever the reason, you will have
formulated some criteria by which to measure success. This section is, therefore, concerned
with the introduction of testing methods aimed at proving success.

Almost certain is the fact that you will need to prove that your device does what it is supposed
to; this is called verification. . In medical device terms…does your output meet the demands
set by your input? By and large this is conducted in a laboratory and is hence in vitro .
Sometimes, but rarely nowadays, some animal experiments are required. But they are all
concerned with verifying that the device performs as expected.

9.3.1 In Vitro/In Vivo
In vitro literally means “in glass” - this comes from the historical concept of all experiments
being conducted using glass test tubes, beakers, and jars. It now covers any experiment
that is not, literally, how it is to be used in real life (in our case on a living human being).
Experiments on human subjects are called an in vivo experiment.

There are two reasons to conduct an in vitro evaluation. The first is to confirm that the
performance characteristics of your device are as designed. The second is to experimentally
evaluate a failure mode in order to reduce the RPN in a risk analysis.

9.3.2 Accelerated Life Tests
One of the most common in vitro evaluations is an accelerated life test. The actual conditions
for the test will come from your PDS and may well be defined by national or international
standards. Those of you with sterile packaged items have a mandatory obligation to conduct
these, but it is just as important for everyone else. Some common environmental parameters
that you may wish to consider are listed in the sections below.