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Table 5. Critical care ventilators (illustrative hypothetical example)

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Contents

Summary Proof Table - for one particular PM-critical device type

Commentary

This table illustrates (with hypothetical data) the acceptability of the reliability and safety of several (hypothetical) manufacturer-model versions of this type of device. According to the illustrative findings shown, it appears that the Velour model of the Carefashion company’s critical care ventilators (whose test results are shown in rows R1 and R2) is demonstrating an unacceptable level of device restoration-related failures when the devices are maintained at a 12 month interval (row R3) – showing an MTBF of only 13 years. This level of poor reliability is not seen when the same devices are maintained at the recommended 6-month interval. In contrast to this, the Coyote company’s Model 300 ventilator (test results shown in rows R3 and R4) still shows an acceptable level of reliability when it is maintained at the longer 12 month interval.

A different and more concerning pattern is seen with the Matelot company’s Model 500 ventilator (rows R7 and R8). It demonstrates an unacceptable level of reliability and safety at both maintenance intervals - apparently related to the poor reliability of the device’s non-durable parts. Based on this evidence this particular model should be characterized as a high-risk (PM Priority 1) device when maintained at either 6 or 12-month intervals.

Yet another pattern is seen with the Herman company’s Uno model ventilator (rows R5 and R6). While it shows acceptable reliability and safety when it is maintained at a 6-month interval, it appears to demonstrate an unacceptable level of performance or safety problems when it is maintained at the longer 12-month interval. Based on this empirical evidence, this particular model should also be characterized as a high-risk (PM Priority 1) device when it is maintained at the 12-month interval. It seems that these particular PM-critical devices - all of which have potentially life-threatening outcomes - show a tendency to become unreliable if the maintenance interval is not carefully controlled.

Clicking on the (active) link in the first field of the table (row R1 column C1) will take you to a Detailed Proof Table (Critical care ventilator/ Carefashion-Velour/ 6 months), which shows all of the separate batches of data that are aggregated into the summary data shown in each row of the Summary Proof Table shown below. This is only an illustration and the other links have not yet been activated.

This table was last updated on 12-10-15

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11
Critical care ventilators Experience base
(# of
device-yrs)
Is size of experience base acceptable?
(See Table 5.2
below)
MTBF
for
DR-related reliability
Level of
Severity of
DR-related
failure modes
Is level of DR-related reliability/safety
acceptable?
(See Table 5.3 below)
PM Priority Level
(DR)
(Table 5.4)
MTBF
for
ST-related reliability
Level of
Severity of
ST-related
failure modes
Is level of ST-related reliability/safety
acceptable?
(See Table 5.3 below)
PM Priority Level
(ST)
(Table 5.4)
R1 Critical care ventilator/ Carefashion-Velour/ 6 months

C.VEN/C1-V1/ 06
1492
dev-yrs
Yes
>500
dev-yrs
=
Substantial
107
years
LOS 3
(Life-
threatening)
Yes
>75-150 yrs
=
Acceptable
- good
PM
Priority
4*
249
years
LOS 3
(Life-
threatening)
Yes
>150 yrs
=
Acceptable
- excellent
PM
Priority
7
R2 Critical care ventilator/ Carefashion-Velour/ 12 months

C.VEN/C1-V1/ 12
80
dev-yrs
Yes
>50-200
dev-yrs
=
Acceptable
13
years
LOS 3
(Life-
threatening)
No
<75 yrs
=
Unacceptable
(= high-risk device)
PM
Priority
1*
80
years
LOS 3
(Life-
threatening)
Yes
75-150 yrs
=
Acceptable
- good
PM
Priority
4
R3 Critical care ventilator/ Coyote-300/ 6 months

C.VEN/C2-N1/ 06
600
dev-yrs
Yes
>500
dev-yrs
=
Substantial
100
years
LOS 3
(Life-
threatening)
Yes
>75-150 yrs
=
Acceptable
- good
PM
Priority
4*
200
years
LOS 3
(Life-
threatening)
Yes
>150 yrs
=
Acceptable
- excellent
PM
Priority
7
R4 Critical care ventilator/ Coyote-300/ 12 months

C.VEN/C2-N1/ 12
150
dev-yrs
Yes
>50-200
dev-yrs
=
Acceptable
75
years
LOS 3
(Life-
threatening)
Yes
>75-150 yrs
=
Acceptable
- good
PM
Priority
4*
150
years
LOS 3
(Life-
threatening)
Yes
75-150 yrs
=
Acceptable
- good
PM
Priority
7
R5 Critical care ventilator/ Hermano-Uno/ 6 months

C.VEN/H1-U1/ 06
800
dev-yrs
Yes
>500
dev-yrs
=
Substantial
90
years
LOS 3
(Life-
threatening)
Yes
>75-150 yrs
=
Acceptable
- good
PM
Priority
4*
267
years
LOS 3
(Life-
threatening)
Yes
>150 yrs
=
Acceptable
- excellent
PM
Priority
7
R6 Critical care ventilator/ Hermano-Uno/ 12 months

C.VEN/H1-U1/ 12
300
dev-yrs
Yes
200-500
dev-yrs
=
Adequate
23
years
LOS 3
(Life-
threatening)
No
<75 yrs
=
Unacceptable
(= high-risk device)
PM
Priority
1*
43
years
LOS 3
(Life-
threatening)
No
<75 yrs
=
Unacceptable
(= high-risk device)
PM
Priority
1*
R7 Critical care ventilator/ Matelot-500/ 6 months

C.VEN/M1-N2/ 06
400
dev-yrs
Yes
200-500
dev-yrs
=
Adequate
40
years
LOS 3
(Life-
threatening)
No
<75 yrs
=
Unacceptable
(= high-risk device)
PM
Priority
1*
200
years
LOS 3
(Life-
threatening)
Yes
>150 yrs
=
Acceptable
- excellent
PM
Priority
7
R8 Critical care ventilator/ Matelot-500/ 12 months

C.VEN/M1-N2/ 12
60
dev-yrs
Yes
50-200
dev-yrs
=
Acceptable
50
years
LOS 3
(Life-
threatening)
No
<75 yrs
=
Unacceptable
(= high-risk device)
PM
Priority
1*
160
years
LOS 3
(Life-
threatening)
Yes
>150 yrs
=
Acceptable
- excellent
PM
Priority
7
  • DR-related failure = device restoration-related failure. A device failure is considered to be a DR-related failure when it can be attributed to inadequate restoration of the device's non-durable parts.
  • ST-related failure = safety testing-related failure. A device failure is considered to be an ST-related failure when it can be attributed to a hidden performance or safety deterioration that was not discovered and repaired during the device's last PM.

Table 5.2 Thresholds for acceptability of the size of the experience base (Still tentative)


Experience base thresholds
(tentative)
Amount of data
(device-yrs)
Inadequate <50
Adequate 50-200
Good 200-500
Substantial >500


Table 5.3 Thresholds for acceptability of the MTBF (mean time between failures) levels for both DR-related reliability and ST-related reliability - for device failures with different Levels of Severity (Still tentative)


Level of reliability
(expressed as an MTBF)
with respect to both
DR-related and ST-related
device failures
LOS 1
(Disruption
of patient
care)
LOS 2
(Possible
patient
injury)
LOS 3
(Life-
threatening
injury)
Unacceptable <25 yrs <50 yrs <75 yrs
Acceptable -
good
25-50 yrs 50-100 yrs 75-150 yrs
Acceptable -
excellent
>50 yrs >100 yrs >150 yrs


Table 5.4 Definitions of the nine different levels of PM Priority and four different levels of device risk (copied from Table 11.)


LOS 3
(Life-
threatening
injury)
LOS 2
(Possible
patient
injury)
LOS 1
(Disruption
of patient
care)
High risk
device
PM Priority 1
(MTBF <75 yrs)
PM Priority 2
(MTBF <50 yrs)
Moderate risk
device
PM Priority 3
(MTBF 75-150 yrs)
PM Priority 4
(MTBF 50-100 yrs)
PM Priority 5
(MTBF <25 yrs)
Low risk
device
PM Priority 6
(MTBF >150 yrs)
PM Priority 7
(MTBF >100 yrs)
PM Priority 8
(MTBF 25-50 yrs)
Very low risk
device
PM Priority 9
(MTBF >50 yrs)


The level of risk associated with a device failing because the PM was not completed in a timely and competent manner is determined by both the level of severity of the possible adverse outcome of the device failing and the device's demonstrated reliability (demonstrated probability of the device failing).

So a device that has at least one high severity failure mode (LOS 3 or LOS 2) combined with a poor demonstrated reliability (MTBF less than 75 yrs for LOS 3, or 50 yrs for LOS 2) should be considered a high-risk device. These two slightly different levels of high-risk devices should also be given corresponding high priorities (PM Priority 1 and PM Priority 2) for completing their PMs in a timely manner.

Devices with better levels of reliability (represented by longer MTBFs) and/or lower severity outcomes should be considered lower risk devices and they should be given correspondingly lower priorities for completing their PMs on time. The full hierarchy of different combinations of the worst-case severity of the result of the device failing and the device's demonstrated reliability is shown in Table 5.4 above.

Note that - if a device has both device restoration-related (DR-R) failure modes and safety testing-related (ST-R) failure modes, and they have different levels of severity and/or reliability, resulting in different levels of risk and PM priority, the overall risk level and PM priority for the device should be set to the more stringent of the two. This preference is shown in the Summary Proof Table (Table 5) above as an asterisked entry in either column C7 or C11.


Abbreviations
DR Device restoration, as in the device restoration-related tasks listed in a device's recommended PM procedure.
ST Safety testing, as in the safety testing-related tasks listed in a device's recommended PM procedure.
Level of Severity (LOS) 1 A device whose failure could be life-threatening i.e. that could cause the patient (or the user) to lose his or her life.
Level of Severity (LOS) 2 A device whose failure could cause a patient injury.
Level of Severity (LOS) 3 A device whose failure could cause a disruption of care, such as, delaying treatment or diagnosis, or requiring one or more patients to be rescheduled.
MTBF Mean Time Between Failures - is the inverse of the device's failure rate. For example, a device that failed twice in nine years has an MTPF of 4.5 years.


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