Electric shock
Electric
shock is an injury caused by an electrical current passing through the body.
The source of the current may be
atmospheric (lightning) or man-made, as in high and low voltage lines.
Injuries
include burns, muscle contractions and seizures, fractures, tissue death, kidney
failure and respiratory and heart failure.
Treatment involves separating the
victim from the current source, re-establishing vital functions and providing
supportive care as required.
Electrical
injury can be avoided by education about electricity and its dangers, and
correct wiring of appliances and houses, including the use of circuit breakers
to prevent short circuits.
What is
electric shock?
Electric shock is injury caused by an electrical current passing
through the body. The electricity may be atmospheric (lightning) or man-made
(high-voltage transmission and low-voltage lines).
Possible
injuries include burns and physiological disturbances, which may range from a
minor burn to death in severe cases.
What
causes electric shock?
Factors that determine the form and severity of injury include:
the
type and magnitude of current,
the
resistance of the body at the point of contact – different tissues in the body
will offer different electrical resistance,
the
current pathway through the body and the
duration
of current flow.
AC,
particularly of the common 50-60 Hz (cycles/second) variety, is three to five
times more dangerous than DC (direct current) of the same voltage and amperage
(current strength).
DC tends
to cause a convulsive contraction of the muscles, often forcing the victim away
from further current exposure.
The
effects of AC on the body depend to a great extent on the frequency:
low-frequency currents (50 – 60 Hz) are usually more dangerous than
high-frequency currents. AC causes muscle spasm, often 'freezing' the hand (the
most common part of the body to make contact) to the circuit. The fist clenches
around the current source resulting in prolonged exposure with severe burns.
Burns from electricity are the result of extremely high temperatures (up to 5000
degrees C) generated at the point of skin contact with the conductor. They
usually involve the skin and the tissues beneath and may be of almost any size
and depth. Generally the higher the voltage and the amperage, the greater the
damage from either type of current.
What
happens to a body subjected to electric shock?
In general, the amount of injury to the body is directly proportional
to the duration of exposure. This is because tissue breakdown occurs with longer
exposure, which allows internal current flow.
Heat is
produced by current flow through tissues, causing:
severe burns
protein coagulation – the proteins in
the cells clump together, destroying the function of the cells
vascular thrombosis – clotting of
blood
tissue
necrosis (tissue death)
Physiologic changes include:
involuntary muscular contractions and
seizures
ventricular fibrillation – a severely
disordered rhythm of the heart which is fatal if not corrected
respiratory
arrest due to central nervous system injury or muscle paralysis
decreased
blood clotting
dehydration
skeletal fractures
Who is
at risk of electric shock?
Anyone who is either ignorant of the potential dangers of electricity
or who doesn’t respect these is at risk.
Symptoms
and signs of electric shock
The effects and clinical signs and symptoms of electrical injuries
depend on a complex interaction of the factors discussed above, and may include
the following:
An
electric shock can startle you and cause you to fall down or be thrown down.
It
may cause severe, rigid contractions of the muscles which in turn may result in
fractures, dislocations and loss of consciousness.
The
respiratory system may be paralysed and the heart may beat irregularly or even
stop beating altogether.
Sharply demarcated electrical burns
may be present on the skin and extend into deeper tissue.
High voltage may cause death of
tissues between the entry and exit point of the current. Massive swelling of the
tissues (oedema) may follow as the blood in the veins coagulates and the muscles
swell.
Low
blood pressure (hypotension), fluid and electrolyte disturbances and the release
of myoglobin (an iron-containing protein present in the muscles) into the
circulation can cause kidney failure.
Bathtub
accident victims, who suffer electric shock while in the water, may show no
burns but suffer cardiac arrest.
Lightning
rarely leaves entry or exit wounds and seldom causes muscle damage or the
release of myoglobin. Coma or other evidence of damage to the nervous system may
occur, but usually resolves within hours or days. Death is usually due to
failure of both the respiratory and cardiac systems.
Can
electric shock be prevented?
Prevention of electrical injuries entails proper design, installation
and maintenance of all electrical devices. Education and compliance with
instructions as to the use of electric appliances, as well as common sense and
respect in dealing with electricity are essential. Any electrical device that
touches or may be touched by the body and has life-threatening potential should
be properly earthed and incorporated in circuits containing fail-safe equipment.
Ground-fault circuit breakers, which trip at current leakage to ground levels of
as low as 5mA, are excellent safety devices and are readily available.
How is
electric shock treated?
Immediate treatment consists of:
separating the victim from the current source,
re-establishing
vital functions and
providing supportive care as required.
Breaking
contact between the victim and the current source can be done either by shutting
off the current or by removing the person from contact with it. Shutting off the
current source, if this can be done rapidly, is the best method (e.g. throwing a
circuit breaker or switch). Disconnecting the device from its electrical outlet
or cutting the wires using insulated tools are other methods.
For low
voltage, the rescuer should use an insulating material (cloth, dry wood, rubber,
leather belt) to pull the victim free.
Once it
has been established that it is safe to touch the victim, a rapid examination
for vital functions (pulse, breathing and level of consciousness) should be
performed. If spontaneous breathing is not observed, or cardiac arrest has
occurred, immediate cardiopulmonary resuscitation (CPR) is required. The victim
should also be treated for shock and taken to hospital for further treatment.
A
tetanus injection is required for any burn. An ECG, cardiac enzymes, full blood
count and a urinalysis are baseline investigations required for all electrical
injuries. Other tests may be indicated when necessary.
Any
suggestion of damage to the heart, abnormal rhythms or chest pain requires
monitoring for at least 24 hours.
Any
deterioration in level of consciousness requires a CT scan to rule out bleeding
into the brain.
What is
the outcome of electrical shock?
The outcome depends on the severity of the incident.
Progressive damage is usually much more severe than the original lesion would
indicate, since the underlying tissues are damaged along the path of the electic
shock through the body.
Extensive burns require long-term hospitalisation and often plastic surgery.
When to
call the doctor
In any case of electrical accident where burns or loss of
conciousness occur you should seek medical attention as soon as possible.
