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Effects of electric current
on human body
What is electric current?
Electric current is a flow of particles having an
electric charge (electrons, positive and negative
ions)…..
What is making the particles to move?
Electric voltage  a difference of electric potentials.
Electric potential is in fact an electric characteristic
of some certain place. …..
We can compare the electric potentials to places of
some “concentration” of the electric charges and
electric voltage to the difference between these
places.
Free charged particles will be moving from highly
concentrated places to places with a low
concentration.
Origin of the lectric current
Electric current can be present in solid substances
(metals), liquids (electrolytes), and gases (ionized
gases).
The substance is able to conduct the electric current only on
condition that contains free charged particles.
Free charged particles of these substances perform only the
thermal motion until the electric voltage is present.
Thermal motion is a random and irregular motion of any
small particle (atom, molecule). The range of the motion
depends on kind of chemical bonds of the particle and
surrounding matter.
If there is an electric voltage (potential difference), free
charged particles start to move in the direction from the
place of the highest electric potential to the place of the
lowest electric potential.
The movement of free charged particles from the place of
highest electric potential to the place of lowest electric
potential is called electric current.
Free charged particles can be either negative (electrons or
negative ions) or positive (positive ions).
What are AC and DC?
• AC is an alternating current, DC is direct current. The
voltage in direct current does not change (a good
example can be a battery).
• The voltage in AC is changing (electrical outlet). Number
of cycles in 1 second is called frequency (measured in
Hertz).
What does the electric current in human
body?
Human tissues are very sensitive to the flow of electric
current.
The electric current flowing through the heart causes the
fibrillation of the heart, flowing through muscles it causes
contractions of the muscles; if the electric current is
passing through the brain it causes the loss of
conciseness and seizures.
The threshold of perception for current entering the hand
is about 5 to 10 miliamperes (mA) for DC and about 1 to
5 mA for AC at 60 Hz.
The maximum amperage that can cause the flexors of the
arm to contract but that allows a person to release his
hand from the current's source is termed the let-go
current.
For DC, the let-go current is about 75 mA for a 70-kg man;
for AC, it is about 15 mA, varying with muscle mass.
AC current traveling through the chest for a fraction of a
second may induce ventricular fibrillation at amperage
as low as 60 to 100 mA; about 300 to 500 mA of DC is
required. If the current has a direct pathway to the heart
(e.g., via a cardiac catheter or pacemaker electrodes), a
much lower amperage (< 1 mA, AC or DC) can produce
fibrillation.
Why is AC more danger than DC?
• The type of current affects the severity of the injury.
• In general, direct current (DC), which has zero frequency,
is less dangerous than alternating current (AC).
• The effects of AC on the body depend largely on the
frequency.
• Low-frequency currents of 50 to 60 Hz (cycles/sec),
which are commonly used, are usually more dangerous
than high-frequency currents and are 3 to 5 times more
dangerous than DC of the same voltage and amperage.
• DC tends to cause a convulsive contraction, often forcing
the victim away from the current's source.
• AC at 60 Hz (household current) produces muscle
tetany, often freezing the hand to the current's source;
prolonged exposure may result, with severe burns if the
voltage is high.
• The human body is in fact the mixture of cells and
extracellular fluid. Inside the cells is intracellular fluid.
The extracellular fluid is an electrolyte that means a
good conductor. The intracellular fluid is also an
electrolyte. The cell membranes are isolants.
• DC  if the voltage that is not changing is applied …the
direct current can flow through the extracellular fluids. It
can not pass through the cell membranes, so it can not
flow intracellulary (contrary to AC ).
Calculation of the current in circuit
• The value of the current flowing through any circuit is
calculated by the equation I = U/R.
Explanation:
• the higher is the voltage (U), the higher is the value of I
(amperage).
• On the other hand the higher is the resistance (R), the
lower is the value of electric current (I).
Example  lets have battery having 4.5 V, the metal wire
with resistance 1 W. What is the value of electric current
flowing through the circuit (amperage)? Result  4,5 A.
• Body resistance (measured in ohms/cm2) is concentrated
primarily in the skin and varies directly with the skin's
condition.
• The resistance of dry, well-keratinized, intact skin averages
20,000 to 30,000 ohms/cm2; for a thickly calloused palm or
sole, it may be 2 to 3 million ohms/cm2.
• The resistance of moist, thin skin is about 500 ohms/cm2.
• If the skin is punctured (e.g., from a cut or abrasion or by a
needle) or if current is applied to moist mucous membranes
(e.g., mouth, rectum, vagina), resistance may be as low as
200 to 300 ohms/cm2.
• If skin resistance is low, few, if any, extensive burns
occur, although cardiac arrest may occur if the current
reaches the heart.
• If skin resistance is high, much energy may be
dissipated at the surface as current passes through the
skin, and large surface burns can result at the entry and
exit points, with charring of tissues in between (heat =
amperage2 × resistance).
• Internal tissues are burned depending on their
resistance; nerves, blood vessels, and muscles conduct
electricity more readily than denser tissues (eg, fat,
tendon, bone) and are preferentially damaged.
• It is clear that much higher voltage must be used to
cause at least minimal effect on human body, because of
the high resistance.
Heat effects of electric current
• The higher the resistance is the higher production of the
heat is. If there is an element with high resistance in the
circuit, it is usually hot, depending on the value of electric
current (amperage) in the circuit and the resistance of the
element.
• If skin resistance is low, few, if any, extensive burns occur,
although cardiac arrest may occur if the current reaches
the heart.
• If skin resistance is high, much energy may be dissipated
at the surface as current passes through the skin, and large
surface burns can result at the entry and exit points, with
charring of tissues in between (heat = amperage2 ×
resistance  Q = I2 . R. t).
Pathogenesis
• The type of current affects the severity of the injury. In
general, direct current (DC), which has zero frequency but
may be intermittent or pulsating, is less dangerous than
alternating current (AC).
• The effects of AC on the body depend largely on the
frequency. Low-frequency currents of 50 to 60 Hz
(cycles/sec), which are commonly used, are usually more
dangerous than high-frequency currents and are 3 to 5
times more dangerous than DC of the same voltage and
amperage.
• DC tends to cause a convulsive contraction, often forcing
the victim away from the current's source. AC at 60 Hz
(household current) produces muscle tetany, often freezing
the hand to the current's source; prolonged exposure may
result, with severe burns if the voltage is high.
• Generally, the higher the voltage and amperage, the
greater the damage from either type of current.
• High-voltage (> 500 to 1000 V) currents tend to cause deep
burns, and low-voltage to cause freezing to the circuit.
• The threshold of perception for current entering the hand is
about 5 to 10 milliamperes (mA) for DC and about 1 to 10
mA for AC at 60 Hz.
• The maximum amperage that can cause the flexors of the
arm to contract but that allows a person to release his hand
from the current's source is termed the let-go current.
• For DC, the let-go current is about 75 mA for a 70-kg
man; for AC, it is about 15 mA, varying with muscle
mass.
• A low-voltage (110 to 220 V), 60-Hz AC current traveling
through the chest for a fraction of a second may induce
ventricular fibrillation at amperage as low as 60 to 100
mA; about 300 to 500 mA of DC is required.
• If the current has a direct pathway to the heart (eg, via a
cardiac catheter or pacemaker electrodes), a much lower
amperage (< 1 mA, AC or DC) can produce fibrillation.
Coffee break
• The pathway of current through the body determines
the nature of injury.
• Current traveling from arm to arm or between an arm
and a foot is likely to traverse the heart and so is much
more dangerous than current traveling between a leg
and the ground.
• Electrical injuries to the head may cause seizures,
intraventricular hemorrhage, respiratory arrest,
ventricular fibrillation or asystole, and, as a late effect,
cataracts.
• The most common entry point for electricity is the hand,
followed by the head.
• The most common exit point is the foot.
• With AC, exit and entry are misnomers, because which site
is the entry and which is the exit cannot be determined.
• More appropriate terms are "source" and "ground.“
• Generally, the duration of current flow through the body
is directly proportional to the extent of injury because
longer exposure breaks tissues down, allowing internal
current flow.
• The current flow produces heat, damaging internal tissues.
Symptoms and Signs
• The clinical manifestations of electrical injuries depend
on the complex interaction of the factors discussed
above.
• Physiologic functions may be altered, resulting in severe
involuntary muscular contractions, seizures, ventricular
fibrillation, or respiratory arrest (apnea) due to CNS
injury or muscle paralysis.
• Thermal, electrochemical, or other damage (eg,
hemolysis, protein coagulation, vascular thrombosis,
dehydration, muscle and tendon avulsion) may occur.
• Often a combination of these effects occurs.
• Burns may be sharply demarcated on the skin and
extend well into deeper tissues.
• High voltage may cause coagulation necrosis of muscle
or other internal tissues between source and ground
points of the current.
• Massive edema may follow as the veins coagulate and
the muscles swell, with resulting compartment
syndromes.
• Hypotension, fluid and electrolyte disturbances, and
severe myoglobinuria may cause acute renal failure.
• Dislocations, vertebral or other fractures, blunt injuries,
and loss of consciousness may result from powerful
muscle contractions or falls secondary to the electric
shock (eg, electricity can startle a person, causing a fall).
• In "bathtub accidents" (typically, when a wet [grounded]
person contacts a 110-V circuit--eg, from a hairdryer or
radio), cardiac arrest may occur without burns.
• Lightning rarely, if ever, produces entry and exit wounds
and seldom causes muscle damage or myoglobulinuria,
because the duration of current is too short to break down
the skin and tissues.
• Lightning flashes over the person, producing little internal
damage other than electrical short-circuiting of systems
(eg, heart asystole, brain confusion, loss of consciousness,
neuropsychologic sequelae).
• Some form of amnesia generally results.
• Neuropsychologic damage, pain syndromes, and
sympathetic nervous system damage are the most
common long-term sequelae.
• Cardiopulmonary arrest is the most common cause of
death.
• Toddlers who suck on extension cords can burn their
mouth and lips. Such burns may cause not only cosmetic
deformities but also growth problems of the teeth,
mandible, and maxilla.
• An added danger is labial artery hemorrhage, which
results when the eschar separates 7 to 10 days after the
injury; hemorrhage occurs in up to 10% of cases.
Symptoms and Signs - CONCLUSION
• Depend on the pathway of electric current through the
body. Conduction from arm to arm or arm to foot is much
more dangerous than the conduction between legs or leg
and the ground since the current may traverse the heart.
• Electrical injuries to the head cause loss of conciseness,
seizures, respiratory arrest. In Czech republic in half of
electric injuries at home children under 5 y are insulted.
• High voltage vs. low voltage injuries (special category 
bathtub accidents) ……..
Treatment
• Contact between the victim and the current source must
be broken.
• The best method is to shut off the current, if it can be
done rapidly (eg, by throwing a circuit breaker or switch,
by disconnecting the device from its electrical outlet);
otherwise, the victim must be removed from contact with
the current.
• For low-voltage (110 to 220 V) currents, the rescuer
should first well insulate himself from ground and then
use an insulating material (eg, cloth, dry wood, rubber,
leather belt) to pull the victim free.
• If lines could be high voltage, no attempt to disengage
the victim should be made until the power is shut off.
• High- and low-voltage lines are not always easily
differentiated, particularly outdoors.
• Once the victim can be safely touched, he should be
rapidly examined for vital functions (eg, radial, femoral,
or carotid pulse; respiratory function; level of
consciousness). Airway stabilization is the first priority. If
spontaneous respiration is not observed or cardiac arrest
has occurred, immediate resuscitation is required (see
Ch. 206). Treatment of shock and other manifestations of
massive burns is discussed in Ch. 276.
• Once vital functions have been reestablished, the full
nature and extent of the injury must be evaluated and
treated. Dislocations, fractures, and cervical-spinal and
blunt injuries should be sought. If myoglobinuria is
present, fluid replacement and alkalinization therapy is
essential to reduce the risk of renal tubular myoglobin
precipitation (see Ch. 276). Mannitol or furosemide may
be indicated to increase renal flow. Tetanus prophylaxis
is required for any burn.
• Baseline assessment for all electric injuries includes an
ECG, cardiac enzymes, a CBC, and urinalysis,
especially for myoglobin. Cardiac monitoring for 12 h is
indicated if there is any suggestion of cardiac damage,
arrhythmias, or chest pain. Any deterioration in the level
of consciousness mandates a CT or MRI scan to rule out
intracranial hemorrhage.
• Victims of lightning injuries may require cardiac
resuscitation, monitoring, and supportive care. Fluid
restriction is the rule because of potential brain edema.
• Children with lip burns should be referred to a
pedodontist or oral surgeon familiar with the evaluation
and long-term care of such injuries.
Treatment – CONCLUSION
• Separating the patient from the current source  cut
off the source (circuit breaker or switch, disconnecting the
device from its electrical outlet). For low voltage (110-220
V), the rescuer should first ensure that he himself is well
insulated from ground, and then use an insulating material
to pull the person free. If it is suspected that higher voltage
lines are involved, it is best to leave the victim alone until
the power can be shut off.
• rapid cardiopulmonary resuscitation (ABC)
• care in hospital  treatment of myoglobinuria +
hyperkalemia, treatment of fractures, treatment of burns.
• Prevention
• Education about and respect for electricity as well as
common sense are essential. Any electric device that
touches or may be touched by the body and may be life
threatening should be properly grounded and
incorporated into circuits containing protective circuitbreaking equipment. Ground-fault circuit breakers, which
trip when as little as 5 mA of current leaks to ground, are
excellent and are readily available. Preventing lightning
strikes involves using common sense and proper
protection devices, knowing the weather forecast, and
having an escape route to an appropriate shelter in
storms.
• Prevention :
• respect in dealing with electricity
• proper design, installation and maintenance of all electric
devices
• education and care about children
Thank you for your attention!