Transcript Hazard of Medical Instrument 2

HAZARD OF MEDICAL INSTRUMENT II
by
Mohd Yusof Baharuddin
Three-Wire Microshock
Situations

A microshock affects the patient when
leakage from the H wire gets to the P
line, either from a stray capacity, dirt,
fluids, or bad insulation.

This leakage current goes directly to the
heart through an insulated catheter (C).
 In
this case, the circuit is completed because the
patient is contacting the chassis.

In part (b), the leakage current flows through
the patient and back to ground through a
second instrument.

In part (c), the H wire opens on one
instrument, and the N wire opens on the
other instrument.

Microshock does not occur because the power
is simply removed by these faults and no
excessive leakage current is generated.

In part (d), an open G- wire in the instrument
on the left causes an increase in P lead
leakage and causes a microshock.
 The
three-wire power cord gives
considerable protection against
macroshock, but it is not so effective
against microshock.
Two-Wire Microshock
Situations
 In
figure (a), the patient coming in
contact with the two grounded chassis
with the two-wire plug receives a
microshock because of voltage
elevation due to high current in the N
wire.
 That
voltage elevation does not exist in
the three-wire case illustrated in figure
(b) because the G wire does not
normally carry a significant current.
 Thus,
the patient does not receive a
microshock due to the protection of the
three-wire power cord.
Attendant-Mediated
Microshock

Microshock is insidious because it cannot
be felt and leaves no tract in the affected
tissue.

It is not large enough to stimulate a perceptible
number of pain cells to give warning.
 Therefore,
an attendant can pass a microshock to a
patient without being aware, except by observing
the symptoms of cardiac arrhythmia in the patient.

In figure (a), the attendant completes the
circuit to a leaky patient lead by holding it
while touching the patient’s catheter.

In part (b), the attendant completes the
circuit by touching a piece of equipment with
a voltage elevation due to a faulty power
cord.

In both cases, the microshock current would
pass through the attendant without his or her
awareness.

Figure (c) illustrates the case where the
attendant provides the path for the leakage
current by touching the patient’s body at a
place other than the catheter.

In this case, the attendant grounds the patient to
complete the path for the leakage.

The basic defense of the patient against attendantmediated microshock is to have the attendant wear
insulating gloves whenever touching a patient with a
CVC (central vessel catheter), including an external
pacemaker.

Also, the attendant should touch a water pipe or a
known grounding point before touching a patient with a
CVC.

The attendant should also touch the patient skin-to-skin
at a site away from the catheter, in order to neutralize
any electrostatic charge on either of them.

This action dissipates any electrostatic
charge that may have accumulated.

This precaution is made in addition to the use of
 antistatic
 bed
garments,
sheets,
 blankets,
 sterile
and
drapes.
Microshock for Ground Wire
Currents

The three-wire plug on equipment protects
patients against certain kinds of
macroshock.

However, it is not as effective in protecting
against microshock.

The figure illustrates a case where the faulty
equipment on the top causes a large current
to flow in the G wire.

That equipment may not even be in the same
room.
 An
air conditioner on the roof.

The large ground currents from that
equipment may cause enough voltage
elevation between the two devices
connected to the patient to result in a
microshock.

The defense against such microshock is to
use a grounding strap between all pieces of
equipment grounded to the patient.

As an added precaution, the room may have
its own electrical circuit to the service entrance
of the power line.
 Any
ground currents would be generated in the
room only.
Summary
Electrical Shocks
Produced by current, not voltage
 Amount of current dependant on body
resistance
 Human body resistance can range between
1000 ohms and 1,000,000 ohms, depending
on body mass, moisture content, and area of
contact

Macroshock vs Microshock
Macroshock current is distributed somewhat
evenly through body parts
 Microshock current path is through a single
point, usually the heart
 Microshock can be fatal at levels that would
be imperceptible if applied to skin

Macroshock
Electrical current that leaks from a broken
cord or piece of equipment
 When passing from hand to hand, only about
5% of the current passes through the heart
 When passing from leg to leg, no current
passes through the heart

Microshock
Term used to describe the very low level
shocks that go undetected
 Dangerous to an “electrically sensitive” patient
– patient with breaks in skin like abrasions,
wet dressings, pacemakers, or monitoring
lines connected to a transducer
 Path of current with an intra-cardiac electrode
