Biomedical Engineering Reference
In-Depth Information
Table 7.13: Example FMEA
Rating
Remedial
1
Display shows insulin
is being infused but no
insulin is entering the body.
Patient can
suffer diabetes
related episode.
There is a leak
in the infusion
line.
4
3
1
12
Occurrence
Detect
=
1
1
2
3
4
5
1
1
2
3
4
5
2
2
4
6
8
10
3
3
6
9
12
15
4
4
8
12
16
20
5
5
10
15
20
25
Rating
Rem
edial
1
Display shows
insulin is being
infused but no
insulin is entering
the body.
Patient
can suffer
diabetes
related
episode.
There is a
leak in the
infusion line.
4
3
1
12
Infusion line
redesigned
to be robust;
fittings to be
tamperproof.
4
2
1
8
CASE STUDY 7.3
Consider a similar insulin pump but one where the display can become “stuck” due to low battery
level. Here the failure is the battery supplies enough power to drive the display, but not enough
the power the pump. Hence the system thinks an infusion has been made, whereas nothing has
happened. Now the detection is impossible for any but a highly skilled engineer, therefore the value
of D has risen to 5. The occurrence of a flat battery is quite commonplace (you should be able
to determine the occurrence from the battery rating), so O is 4. The overall RPN is 80, and
Table
7.14
shows that this is heavily in the “intervention required” zone and as a consequence must have
remedial action. The system was redesigned to incorporate a “buzzer” when the battery is getting low
(note not flat). An emergency battery pack was included so that in cases where the charger could not
be used the system would still work for 8 hours. This meant that the occurrence has dropped to 2, as
it is now rare, and the detection has dropped to 1. The new RPN is 8 and hence acceptable.
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