Electric shock

Electric shock from artificial sources occurs as a result of its passage through the human body. Symptoms may include skin burns, damage to internal organs and soft tissues, cardiac arrhythmias and respiratory arrest. Diagnosis is established in accordance with clinical criteria and laboratory test data. The treatment of electric shock is supportive, aggressive - with severe injuries.

Although accidents with electricity at home (for example, touching electrical outlets or electric shock by a small device) rarely lead to significant damage or consequences, in the US every year, approximately 400 accidents involving high-voltage current end fatal.

[1], [2], [3]

Pathophysiology of electric shock

Traditionally, the severity of electrical injury depends on six factors Covenhoven:

• type of current (constant or variable);
• voltage and power (both values describe the current strength);
• duration of exposure (the longer the contact, the heavier the damage);
• body resistance and current direction (depends on the type of damaged tissue).

However, the electric field stress, a newer concept, seems to predict the severity of the injury more accurately.

Factors of the Covenhoven. Alternating current often changes direction. This type of current usually supplies electrical outlets in the US and Europe. The constant current flows constantly in the same direction. This is the current produced by the batteries. Defibrillators and cardioverters usually deliver a direct current. The way in which an alternating current affects the body depends to a large extent on its frequency. Alternating current low frequency (50-60 Hz) is used in home networks of the USA (60 Hz) and Europe (50 Hz). This can be more dangerous than a high frequency AC and 3-5 times more dangerous than a direct current of the same voltage and force. Low-frequency alternating current causes a prolonged contraction of the muscles (tetany), which can "freeze" the hand to the current source, thus prolonging the electrical effect. Constant current, as a rule, causes a single convulsive contraction of the muscles, which, usually, discards the victim from a current source.

Usually both for alternating current and for constant current is typical: the higher the voltage (V) and the current strength, the greater the resulting electric injury (for the same duration of exposure). The domestic current in the USA is from 110 V (standard electrical output) to 220 V (large device, such as a dryer). High voltage current (> 500 V), as a rule, leads to deep burns, and a low-voltage current (110-220 V) usually causes a muscle spasm - tetany, freezing the victim to a current source. The threshold of perception of the DC current entering the hand is approximately 5-10 mA; for an alternating current of 60 Hz, the threshold is on the average 1-10 mA. The maximum current that can not only cause the flexors of the hand to contract, but also allows the brush to release the current source, is called "release current". The magnitude of the release current varies depending on the body weight and muscle mass. For a medium-sized person with a body weight of 70 kg, the release current is approximately 75 mA for the forward and approximately 15 mA for alternating currents.

A low-voltage alternating current with a frequency of 60 Hz, passing through the chest for a second, can cause ventricular fibrillation at such low current intensity as 60-100 mA; for a constant current, approximately 300-500 mA is required. If current flows directly into the heart (for example, through a cardiac catheter or pacemaker electrodes), a current of <1 mA (alternating or constant) can cause ventricular fibrillation.

The amount of dispersed heat energy of high temperature equals the current strength of the resistance time. Thus, with a current of any force and duration of exposure, the tissue even with the highest degree of stability can be damaged. The electrical resistance of the tissue, measured in Ohm / cm2, is determined primarily by skin resistance. The thickness and dryness of the skin increase resistance; dry, well keratinized, intact skin has an average resistance value of 20 000-30 000 Ohm / cm2. For a calloused palm or foot, the resistance can reach 2-3 million Ohm / cm2. For a damp, thin skin, the resistance averages 500 ohm / cm2. Resistance to damaged skin (for example, a cut, abrasion, needle puncture) or moist mucous membranes (for example, the mouth, rectum, vagina) may not be more than 200-300 ohm / cm2. If the skin resistance is high, it can scatter a lot of electrical energy, which results in large burns at the entry and exit points of the current with minimal internal damage. If the skin resistance is low, skin burns are less extensive or absent, but more electrical energy can dissipate in the internal organs. Thus, the absence of external burns does not exclude the absence of electrotrauma, and the severity of external burns does not determine its severity.

Damage to internal tissues also depends on their resistance and in addition to the density of the electric current (current per unit area, the energy is more concentrated when the same flow passes through a smaller area). So, if the electrical energy enters through the arm (primarily through lower-resistance tissues, for example, muscle, vessel, nerves), the density of the electric current increases in the joints, because of the significant proportion of the cross-sectional area of the joint consisting of higher resistance tissues for example, bone, tendon), in which the volume of tissues of lower resistance is reduced. Thus, damage to tissues with less resistance (ligaments, tendons) is more pronounced in the limb joints.

The direction of the current (loop) passing through the victim determines which structures of the body are damaged. Since the alternating current continuously and completely reverses the direction, the commonly used terms "input" and "output" in this case are not entirely acceptable. The terms "source" and "earth" can be considered the most accurate. A typical "source" is a hand, followed by a head. The foot refers to the "earth". The current passing along the path "hand-arm" or "arm-leg", as a rule, passes through the heart and can cause arrhythmia. This current path is more dangerous than passing from one leg to the other. The current passing through the head can damage the central nervous system.

Electric field voltage. The voltage of the electric field determines the degree of tissue damage. For example, when a current of 20,000 V (20 kV) passes through the head and the entire human body, an electric field of about 10 kV / m is generated about 2 m in height. Similarly, a current of 110 V, which has only passed through 1 cm of tissue (for example, through the baby's lip), creates an electric field of 11 kV / m; this is why a low voltage current, passing through a small volume of tissue, can cause the same severe damage as a high voltage current that has passed through a large volume of tissues. Conversely, if we first consider the voltage, and not the strength of the electric field, small or minor electrical injuries can be classified as high voltage damage. For example, an electric shock, received by a man from rubbing his foot on a carpet in the winter, corresponds to a voltage of thousands of volts.

Pathology of electric shock

Exposure to an electric field of low voltage leads to an immediate unpleasant sensation (resembling a stroke), but rarely ends in severe or irreversible damage. Exposure to a high voltage electric field can cause thermal or electrochemical damage to internal tissues, which can include hemolysis, protein coagulation, coagulation necrosis of muscles and other tissues, vascular thrombosis, dehydration and muscle and tendon ruptures. The impact of the high-voltage electric field can result in massive edema that occurs as a result of coagulation of the veins, edema of the muscles and the development of compartmental syndrome. Massive edema can also cause hypovolemia and arterial hypotension. The destruction of muscles can cause rhabdomyolysis and myoglobinuria. Myoglobinuria, hypovolemia and arterial hypotension increase the risk of acute renal failure. Violations of the electrolyte balance are also possible. The consequences of organ dysfunction do not always correlate with the amount of tissue destroyed (for example, ventricular fibrillation may occur against a background of relatively small destruction of the heart muscle).

Symptoms of electric shock

Burns can have sharply outlined boundaries on the skin, even when the current penetrates irregularly into deeper tissues. There may be expressed involuntary muscle contractions, seizures, ventricular fibrillation, or respiratory arrest due to damage to the CNS or muscle paralysis. Damage to the brain or peripheral nerves can cause various fallouts of neurological functions. Cardiac arrest is possible without burns in case of an accident in the bathroom [when a wet (grounded) person is contacted with a 110 V network current (for example, from a hair dryer or radio)].

Small children who bite or suck out elongated wires can get a burn of the mouth and lips. Such burns can cause cosmetic deformities and worsen the growth of teeth, lower and upper jaws. Approximately 10% of such children after bleeding of the scab on the 5-10th day bleed from the buccal arteries.

Electric shocks can cause severe muscle contractions or falls (for example, from a ladder or roof) that end in dislocations (electric shock is one of the few reasons for a posterior dislocation of the shoulder), fractures in the spine and other bones, internal injuries and loss of consciousness.

Diagnosis and treatment of electric shock

First of all, it is necessary to interrupt the contact of the victim with a power source. It is best to disconnect the source from the network (turn off the switch or pull the plug from the mains). If the current can not be quickly disconnected, the victim must be removed from the power source. At a low voltage current, rescuers should first isolate themselves well, and then, using any insulating material (for example, cloth, dry stick, rubber, leather belt), impact or pulling the victim away from the current.

Caution: If the wire can be under high voltage, you can not attempt to release the victim until the line is de-energized. It is not always easy to distinguish high voltage lines from low voltage, especially in the open air.

The affected, exempted current, is examined to identify signs of cardiac arrest and / or respiration. Then they begin to treat shock, which can result from trauma or massive burns. After the end of the primary resuscitation, the patient is fully inspected (from head to toe).

In patients without symptoms, in the absence of pregnancy, concomitant heart diseases, as well as in the short-term exposure to the current of the home network, in most cases there is no significant internal or external damage. You can let them go home.

Other patients should determine the feasibility of performing ECG, OAK, determination of the concentration of the heart muscle enzymes, general urine analysis (in particular for detecting myoglobinuria). Within 6-12 hours, cardiomonitoring is performed for patients with arrhythmias, pain in the chest, other clinical signs indicating possible cardiac abnormalities; and, probably, to pregnant women and patients with a cardiologic anamnesis. In case of impaired consciousness, CT or MRI is performed.

Pain from electric burn is stopped by intravenous injection of opioid analgesics, with caution titrating the dose. When myoglobinuria alkalizing urine and maintaining adequate diuresis (about 100 ml / h in adults and 1.5 ml / kg per hour in children) reduces the risk of kidney failure. Standard formulas for calculating the volume for recovering lost fluid based on burn area underestimate the fluid deficit in burns with electricity, which makes their use impractical. Surgical reorganization of a large volume of affected muscular tissue can reduce the risk of renal failure due to myoglobinuria.

Adequate prevention of tetanus and treatment of burn wounds are necessary. All patients with significant electrical burns should be referred to a specialized burn unit. Children with burns of the lips need an examination of a children's dentist or a dental surgeon who has experience in the treatment of such injuries.

[4], [5], [6], [7]

Prevention of electric shock

Electrical devices for which contact with the body is possible must be isolated, grounded and included in a network equipped with special devices for instantaneous disconnection of the electrical device from the power source. The use of circuit breakers that disconnect the circuit with a leakage current of only 5 mA is most effective for preventing electric shock and electric injury, and therefore they must be used in practice.