Effects of electric current on human body
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
...
What is the resistance of moist thin skin?
0,5 kOhms/cm2
What is the threshold of perception for current entering the hand for AC?
1-5 mA (at 60 Hz)
What is the resistance of dry well-keratinized intact skin?
20-30 kOhms/cm2
How many times more dangerous are AC than DC of the same voltage and amperage?
3-5 times
What is the threshold of perception for current entering the hand for DC?
5-10 mA
What is the household current?
50-60 Hz AC
How much is high-voltage?
>500 to 1000 V
What do DC tends to cause?
A convulsive contraction, often forcing the victim away from the current´s source
What is electric voltage?
A difference of electrical potentials
What is electric current?
A flow of particles having an electric charge (electrons, positive and negative ions)
What is an electrolyte?
A good conductor
What can induce ventricular fibrillation?
A low-voltage AC current (110-220 V, 50-60 Hz) traveling through the chest, at amperage as low as 60-100 mA, for DC 300-500 mA is required
What is the "let-go current" for AC?
About 15 mA, varying with muscle mass
What is the "let-go current" for DC?
About 75 mA for a 70 kg man
What is AC?
Alternating current The voltage is changing (electrical outlet)
What is electric current measured in?
Ampere
What is an electrical potential?
An electrical characteristic of certain place
Why s the duration of current flow through the body directly proportional to the extent of injury
Because longer exposure breaks down tissues and allowing internal current flow
How is electrical voltage measured?
Between two electrical potentials (places)
How to treat people with electrical damage?
Break contact of victim and current source by shutting off the current or move the victim
What does any deterioration in the level of consciousness mandates?
CT or MRI scan to rule out intracranial hemorrhage
What can occur during "bathtub accidents"?
Cardiac arrest without burns
What is the most common cause of death of lightening?
Cardiopulmoary arrest
What does electric current flowing through muscles cause?
Contractions
What do high-voltage currents tend to cause?
Deep burns
What is DC?
Direct current The voltage does not change (battery)
What can powerful muscle contractions, or falls secondary to the electric shock, result in?
Dislocations, vertebral or other fractures, blunt injuries, and loss of consciousness
What is the resistance of punctured skin or skin with moist mucous membranes?
Down to 0,2-0,3 kOhms/cm2
What is the baseline assessment for all electric injuries?
ECG, cardiac enzymes and urinalysis, especially for myoglobin
What does lightening cause?
Entry and exit wounds, and seldom muscle damage or myoglobulinuria because the duration of current is too short to break down the skin and tissues
What should you do if the victim can be safely touched?
Examinate for vital functions (pulse, respiratory function, consciousness) Airway stabilization
What can happen if the skin resistance is low?
Extensive burns, cardiac arrest may occur
70 mA can be ..
Fatal
1 mA can be ..
Felt
What does electric current flowing through the heart cause?
Fibrillation of the heart
How to rescue people with electrical damage from low voltage (110-220 V) currents?
First well insulate yourself from ground and then use an insulating material to pull the victim free
How do you treat myoglobinuria?
Fluid replacement and alkalinization therapy is essential to reduce the risk of renal tubular mypglobin precipitation
What are the reason of charged particles movement?
Free charged particles move from places with high concentration to places with low concentration
What do low-voltage currents tend to cause?
Freezing to the circuit
What are the number of cycles in 1 second in AC called?
Frequency, measured in Hertz
Higher voltage and amperage leads to ...
Greater damage
What other damages can occur of lightening ?
Heart asystole, brain confusion, loss of consciousness, neuropsychologic sequelae
What do current flow produce?
Heat, damaging internal tissue
High resistance equals to ..
High production of heat
What can result in acute renal failure?
Hypotension, fluid and electrolye disturbances and severe myoglobinuria
Explain the equation I = U/R
I - electric current U - voltage R - resistace The higher the voltage (U), the higher is the value of I (amperage) On the other hand, the higher the resistance (R) is, the lower is the value of electric current
Equation of electric current
I = Q/t (A)
Which equation express the current flowing through any circuit?
I = U/R
When is a substance able to conduct the electrical current?
If it contains free charged particles
When is cardiac monitoring used?
If there is any suspicion of cardiac damage, arrhythmias or chest pain
Where can electric current be present?
In solid substances (metals), liquids (electrolytes) and gases (ionized gases)
What are the cell membranes?
Isolants
What does the effects of AC on the body depend on?
Largely on the frequency
>15 mA causes ..
Loss of muscle control
Which internal tissues are preferentially damaged by electric current?
Low density tissues that conduct electricity easy, like nerves, blood vessels and muscles
What can occur when the veins coagulate and muscles swell?
Massive edema
What happens if the 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
What do household current (50-60 Hz) cause?
Muscle tetany, often freezing the hand to the current´s source; prolonged exposure may result, with severe burns if the voltage is high
What are the most common long-term consequences of lightening?
Neuropsychologic damage, pain syndromes, and sympathetic nervous system damage
Can DC pass through the cell membranes and flow intracellular?
No
How to rescue people with electrical damage from high voltage currents?
No attempt to disengage the victim before the power is shut off
What is electric current?
Number of charged particles, which flow through a cross-section conductor in the defined time
What is body resistance measured in?
Ohms/cm2
5 mA is ...
Painful
Where is the body resistance concentrated?
Primarly in the skin and varies directly with the skin´s condition
What injuries can current to the head cause?
Seizures, intraventricular hemorrhage, respiratory arrest, ventricular fibrillation or asystole, and as a late effect cataracts
What can altered physiologic functions after electrical current result in?
Severe involuntary muscular contractions, seizures, ventricular fibrillation or resperatory arrest (apnea) due to CNS injury or muscle paralysis
What happens when a electrical potential is present?
The charged particles start to move in the direction from the place of the highest potential to the place of the lowest potential
Wat does the clinical manifestations of electrical injuries depend on?
The complex interaction of the factors
What does the damage caused by electric shock depend on?
The current flowing through the body
What is the most common exit point for electricity?
The foot
What is the most common entry point for electricity?
The hand, followed by the head
What does electric current flowing through the brain cause?
The loss of conciseness and seizures
What is "let-go current"?
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
Which type of current traveling through the body is most dangerous?
The ones that is likely to transverse the heart, like from arm to arm, arm to foot
What happens with the free charged particles when the electric voltage is present?
The particles start to move in the direction from the place of the highest electric potential to the place of the lowest electric potential
What does free charged particles perform until the electric voltage is present?
The thermal motion
What other damage can occur after electrical current?
Thermal, electrchemical, hemolysis, protein coagulation, vascular thrombosis, dehydration, muscle and tendin avulsion
What are "bathtub accidents"?
Typically, when a wet (grounded) person contacts a 110-220 V circuit (from a hairdryer or radio)
When can a current lower than mA (AC or DC) cause fibrillation of the heart?
When the current has a direct pathway to the heart (e.g. via a cardiac catheter or pacemaker electrodes)
Are human tissues sensitive to the flow of electric current?
Yes
Can AC pass through the cell membranes and flow intracellular?
Yes
Is DC (zero frequency) less dangerous than AC?
Yes
Is low-frequency currents of 50-60 Hz (cycles/s) more dangerous than high-frequency currents ?
Yes
Is the duration of current flow through the body directly proportional to the extent of injury?
Yes
Is the extracellular fluid an electrolyte?
Yes
Is the intracellular fluid an electrolyte?
Yes
