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 arrhythmia, and respiratory arrest. Diagnosis is established according to clinical criteria and laboratory data. Treatment for electric shock is supportive, aggressive - for severe injuries.

Although electrical accidents in the home (such as touching electrical outlets or being shocked by a small appliance) rarely result in significant injury or consequences, approximately 400 high-voltage accidents result in death each year in the United States.

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Pathophysiology of electrical injury

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

• type of current (direct or alternating);
• voltage and power (both quantities describe current strength);
• duration of exposure (the longer the contact, the more severe the damage);
• body resistance and direction of current (depending on the type of damaged tissue).

However, electric field voltage, a newer concept, appears to be a more accurate predictor of injury severity.

Cowenhoven factors. Alternating current (AC) often changes direction. This is the type of current that typically powers electrical outlets in the United States and Europe. Direct current (DC) flows in the same direction continuously. This is the current produced by batteries. Defibrillators and cardioverters typically deliver DC current. The effect of AC on the body depends largely on its frequency. Low frequency AC (50-60 Hz) is used in household electrical outlets in the United States (60 Hz) and Europe (50 Hz). It can be more dangerous than high frequency AC and 3-5 times more dangerous than direct current of the same voltage and amperage. Low frequency AC causes prolonged muscle contraction (tetany), which can freeze the hand to the current source, thus prolonging the electrical effects. Direct current (DC) usually causes a single convulsive muscle contraction, which usually throws the victim away from the current source.

Generally, for both AC and DC current, the higher the voltage (V) and current, the greater the electrical injury that occurs (for the same duration of exposure). Household current in the United States ranges from 110 V (a standard electrical outlet) to 220 V (a large appliance such as a dryer). High-voltage current (>500 V) typically causes deep burns, while low-voltage current (110-220 V) typically causes muscle spasm, or tetany, freezing the victim to the current source. The threshold for perception of direct current entering the hand is approximately 5-10 mA; for alternating current at 60 Hz, the threshold is on average 1-10 mA. The maximum current that can not only cause the flexors of the hand to contract, but also allow the hand to release the current source is called the "let-go current." The magnitude of the let-go current varies depending on body weight and muscle mass. For an average sized person weighing 70 kg, the release current is approximately 75 mA for direct current and approximately 15 mA for alternating current.

Low-voltage alternating current at 60 Hz passed through the chest for one second can induce ventricular fibrillation with currents as low as 60-100 mA; for direct current, approximately 300-500 mA is required. If current is applied directly to the heart (e.g., via a cardiac catheter or pacemaker leads), currents <1 mA (AC or DC) can induce ventricular fibrillation.

The amount of dispersed thermal energy of high temperature is equal to the current strength and resistance time. Thus, at any current strength and duration of exposure, even the most resistant tissue can be damaged. The electrical resistance of tissue, measured in Ohm/cm2, is determined primarily by the resistance of the skin. The thickness and dryness of the skin increase the resistance; dry, well-keratinized, intact skin has an average resistance value of 20,000-30,000 Ohm/cm2. For a callused palm or foot, the resistance can reach 2-3 million Ohm/cm2. For moist, thin skin, the resistance is on average 500 Ohm/cm2. The resistance of damaged skin (e.g., a cut, abrasion, needle puncture) or moist mucous membranes (e.g., mouth, rectum, vagina) may not be higher than 200-300 Ohm/cm2. If the skin resistance is high, a lot of electrical energy can be dissipated in it, resulting 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 be dissipated in the internal organs. Thus, the absence of external burns does not exclude the absence of electrical trauma, and the severity of external burns does not determine its severity.

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

The direction of the current (loop) passing through the victim determines which body structures are damaged. Since alternating current continuously and completely changes direction, the commonly used terms "input" and "output" are not entirely appropriate. The terms "source" and "ground" are considered the most accurate. A typical "source" is the hand, followed by the head. The foot is related to "ground". Current passing through the "hand-to-hand" or "hand-to-foot" path usually passes through the heart and can cause arrhythmia. This current path is more dangerous than passing from one foot to the other. Current passing through the head can damage the central nervous system.

Electric field strength. The electric field strength determines the extent of tissue damage. For example, passing a current of 20,000 volts (20 kV) through the head and entire body of a person about 2 m tall creates an electric field of approximately 10 kV/m. Likewise, a current of 110 volts passing through just 1 cm of tissue (for example, through a 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 just as severe damage as a high-voltage current passing through a large volume of tissue. Conversely, if voltage is considered primarily rather than the strength of the electric field, minor or insignificant electrical injuries can be classified as high-voltage injuries. For example, the electric shock a person receives from rubbing their foot on a carpet in winter corresponds to a voltage of thousands of volts.

Pathology of electric shock

Exposure to low-voltage electric fields causes an immediate unpleasant sensation (similar to a shock), but rarely results in serious or irreversible damage. Exposure to high-voltage electric fields can cause thermal or electrochemical damage to internal tissues, which may include hemolysis, protein coagulation, coagulative necrosis of muscle and other tissues, vascular thrombosis, dehydration, and ruptures of muscles and tendons. Exposure to high-voltage electric fields can result in massive edema, which occurs as a result of venous coagulation, muscle edema, and the development of compartment syndrome. Massive edema can also cause hypovolemia and arterial hypotension. Muscle destruction can cause rhabdomyolysis and myoglobinuria. Myoglobinuria, hypovolemia, and arterial hypotension increase the risk of acute renal failure. Electrolyte imbalances are also possible. The consequences of organ dysfunction do not always correlate with the amount of tissue destroyed (for example, ventricular fibrillation can occur against the background of relatively minor destruction of the heart muscle).

Symptoms of Electric Shock

Burns may be sharply demarcated on the skin, even when the current penetrates irregularly into deeper tissue. Severe involuntary muscle contractions, seizures, ventricular fibrillation, or respiratory arrest may occur due to CNS damage or muscle paralysis. Brain or peripheral nerve damage may cause various neurological deficits. Cardiac arrest is possible without burns in a bathroom accident [when a wet (grounded) person comes into contact with 110 V mains current (e.g., from a hair dryer or radio)].

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

Electric shock can cause violent muscle contractions or falls (such as from a ladder or roof) resulting in dislocations (electric shock is one of the few causes of posterior shoulder dislocation), fractures of the spine and other bones, damage to internal organs, and loss of consciousness.

Diagnosis and treatment of electric shock

First of all, it is necessary to interrupt the victim's contact with the current source. It is best to disconnect the source from the network (turn the switch or pull the plug from the network). If it is impossible to quickly turn off the current, the victim must be pulled away from the current source. With low-voltage current, rescuers must first isolate themselves well, and then, using any insulating material (for example, fabric, a dry stick, rubber, a leather belt), push the victim away from the current by hitting or pulling.

Caution: If the line may be under high voltage, do not attempt to free the victim until the line has been de-energized. Distinguishing high-voltage from low-voltage lines is not always easy, especially outdoors.

The victim, freed from the current, is examined for signs of cardiac and/or respiratory arrest. Treatment is then started for shock, which may result from trauma or massive burns. After the initial resuscitation is completed, the patient is examined completely (from head to toe).

In patients without symptoms, in the absence of pregnancy, concomitant heart disease, and in cases of short-term exposure to household current, in most cases there is no significant internal or external damage and they can be sent home.

In other patients, it is necessary to determine the appropriateness of performing an ECG, CBC, determination of the concentration of cardiac muscle enzymes, general urine analysis (in particular to detect myoglobinuria). For 6-12 hours, cardiac monitoring is performed in patients with arrhythmias, chest pain, other clinical signs indicating possible cardiac disorders; and, possibly, in pregnant women and patients with a cardiac history. In cases of impaired consciousness, CT or MRI is performed.

Pain from an electrical burn is treated with intravenous opioid analgesics, titrating the dose with caution. In myoglobinuria, alkalinization of the urine and maintenance of adequate diuresis (about 100 ml/h in adults and 1.5 ml/kg per hour in children) reduces the risk of renal failure. Standard volumetric fluid replacement formulas based on burn area underestimate the fluid deficit in electrical burns, making their use inappropriate. Surgical debridement of a large volume of damaged muscle tissue can reduce the risk of renal failure due to myoglobinuria.

Adequate tetanus prophylaxis and burn wound care are essential. All patients with significant electrical burns should be referred to a specialized burn unit. Children with lip burns should be evaluated by a pediatric dentist or oral surgeon experienced in treating such injuries.

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Prevention of electric shock

Electrical devices that may come into contact with the body must be insulated, grounded, and connected to a network equipped with special devices for instantly disconnecting the electrical device from the power source. The use of switches that disconnect the circuit when a current leaks by only 5 mA is most effective in preventing electric shock and electrical injury, and therefore they must be used in practice.