Page 113 - Safety Risk Management for Medical Devices

92 Safety Risk Management for Medical Devices

Figure 12.10 Relationship between Use-Misuse Failure Modes and Effects Analysis (UMFMEA) and
the Risk Assessment and Control Table (RACT).

realized due to a use Failure Mode. Fig. 12.10 is applicable to both integral and
distributed Systems.
P 1 , the probability of occurrence of the Hazardous Situation is influenced by the
Occ rating in the System FMEAs. “Influenced” means that P 1 is estimated based on
the contributions from all aspects of the System design, and not any single FMEA.
For example, imagine an infusion pump. A nurse could erroneously enter a wrong
dose on the pump’s UI. But the pump could be linked to the hospital database, which
has the prescription for the patient. The pump could cross-check the entered dose
against the patient’s prescription, and if there is a large enough variation, the pump
could alert the nurse to a possible error. In this scenario, Occ 5 the probability of the
use-error, is not the same as P 1 the probability of patient exposure to an over/under
dose. Also, P 1 is the probability of the occurrence of the Hazardous Situation. Occ
rating from System FMEAs can only indicate the probability of occurrence of the
Hazard, not the exposure to the Hazard(s).

12.6 DESIGN FAILURE MODES AND EFFECTS ANALYSIS
DFMEA is performed to assess the weaknesses that are present in the product and can
be controlled by design. As with other FMEAs, DFMEA is a team activity. A sug-
gested composition for the DFMEA team is:
• Design engineering
• System engineering
• Quality
• Clinical/Medical
• Risk management

It is best if DFMEA is done early in the design and development phase.
Preliminary DFMEAs can and should be done on high-level designs, before all the
details are known.