This application note discusses the findings of the
root cause analysis for NBP hardware failures, the
role that cuff cleaning and disinfection plays in the
failures, and what users can do to maximize the
lifetime of their instruments and cuffs.
Root cause analysis of failures
Triggered by customer feedback about early and
frequent failures of the NBP measurement
hardware in the X1 (M3001A) and X2 (M3002A)
multi measurement modules, and MP2 (M8102A)
and MP5/5T/5SC (M8105A/AT/AS) monitors, a
root cause analysis was performed on returned
The majority of reports indicated that the NBP
pump fails to run when a blood pressure
measurement is started. Some customers reported
that the failure was intermittent and that they were
able to start the pump by tapping on the device
housing, or disconnecting and reconnecting the X1/
X2 module. Other failures included leakage.
Analysis using visual inspection, electron
microscopy, and energy dispersive X-ray
spectroscopy (an analytical tool used for chemical
characterization) showed that the vast majority of
failures were caused by contamination of the
pneumatic system with residuals from:
Figure 1: Example of a contaminated pneumatic
system that clearly shows liquids, white crystals
(that is, residuals from cleaners or disinfectants),
and corrosion at the pump.
• cleaners and disinfectants, and their fumes which
in turn oxidized the copper contact of the motor
• cotton fibers and particles from the inside of the
cuff bladder, and other non-conductive deposits
on the commutator contacts.
How is the pneumatic system infiltrated?
The only plausible explanation is that liquids entered the cuff bladder
and/or hose during cleaning, disinfection or sterilization and were
subsequently flushed into the pneumatic system of the instrument
during cuff deflation.
As neither Philips cuffs and hoses nor the instrument itself contain
cotton, we suspect either that third party cuffs were used on these
instruments, or the cuffs were washed in a washing machine.
Figure 2: Picture from
an electron microscope
showing cotton fibers in
front of the deflation
The particles found in the pneumatic system are most likely to
originate from the inside of the cuffs that were used.
Figure 3: Picture from
an optical microscope
showing a particle at the
valve seat which caused
How does corrosion affect the start-up behavior
of the pump?
In additional investigations the motor current was measured over time
and showed spikes and a strong flashing arc at the commutator gap,
both an indication for high contact resistance.
If the motor stops at this specific position (with high resistance) it may
not be able to be restarted. As some customers already observed,
tapping the device (or disconnecting and reconnecting the X1/X2
module) may move the motor slightly from this position and as a result
the contacts are moved from the area with the high resistance, and the
motor can be restarted.
Figure 4: Example of a
showing oxidation and
on the commutator
contacts and extensive
Figure 5: Motor current
over time showing spikes
which indicate a high
How does infiltration and corrosion occur?
Several factors influence oxidation and/or the deposit of nonconductive material at the commutator contacts. The air inside the
cuff is flushed through the NBP assembly and is so brought into
contact with the motor. Oxidation and deposit of non-conductive
material can be increased by special chemicals/gases/particles which
may come from disinfectants, cuffs or hoses used (when using nonPhilips accessories), or from the environment. The likelihood of this
condition occurring is increased by seldom usage of the pumps.
What can be done when the issue appears?
1. Set the patient category to adult/pediatric.
2. Start an NBP measurement with no cuff attached. This will let the
pump run for 120 sec. and will then stop with an INOP message.
3. Repeat this step for five to ten times.
The start behavior of the pump usually improves.
If this procedure shows no improvement, the NBP pump needs to be
Figure 6: Motor current
over time after
consecutive starts in
adult mode (spikes
Please do not perform this step more than 10 times in succession as
this can overheat the pump motor.
How can these failures be prevented?
Unfortunately, there is no practical solution to prevent ingress of
liquid into the instrument once it has entered the bladder or hose.
Filters suitable for the flow rates required to inflate and deflate cuffs
within an acceptable time are much too large. They would dampen the
measured signals and thus compromise the ability to derive readings
for critically ill patients. Water traps would not only be too large, but
also orientation dependent.
Consequently, the only way to prevent these failures is to prevent the
ingress of liquid and any other substances and particles into the
bladders and hoses.
To maximize the lifetime of your instruments and cuffs:
- Never immerse cuffs, bladders, hoses or connectors in liquid.
- Do not wash cuffs. Closely follow the instructions supplied with
the cuff, that is wipe cuffs with a lint-free cloth dampened with
one of the recommended cleaners or disinfectants.
- If you suspect that liquid has entered the cuff or hose, do not use
this cuff or hose anymore and dispose of it. It will never dry out
completely again because there is very little venting. Use Philips
cuffs and accessories only. Other cuffs and accessories may
contain particles, substances or chemicals that may interact with
components of the pneumatic system to cause failure of the
For Comfort Cuffs only (M157xA):
- Put the protective cap over connector whenever the cuff is not in
use, especially during cleaning, disinfection and sterilization.
- If the outer cover requires more rigorous cleaning, remove the
air bladder first.
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4522 962 85561 MAY 2012