Electric shock: how to evaluate and how to do it | emergency live

2021-11-26 07:02:51 By : Mr. Xinchao He

Emergency live broadcast-pre-hospital care, ambulance service, fire safety and civil defense magazine

In the United States, there are more than 30,000 non-fatal electrical accidents each year, and electrical burns account for approximately 5% of the number of hospital admissions to burn units in the United States.

Traditionally, the severity of electric shock injuries depends on Kouwenhoven factors:

However, the electric field strength, a quantity that has recently been taken into account, seems to more accurately predict the severity of the injury.

Alternating current changes direction frequently; it is the type of electrical current usually supplied to households in the United States and Europe.

Direct current flows continuously in the same direction; it is the type of current provided by a battery.

Defibrillators and cardioversion devices usually provide direct current.

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The way that alternating current harms the body depends largely on the frequency.

Home systems in the United States (60 Hz) and Europe (50 Hz) use low-frequency alternating current (50-60 Hz).

Because low-frequency alternating current can cause violent muscle contraction (hands and feet twitches), you can lock your hands on the power source to extend the exposure time, so it is more dangerous than high-frequency alternating current and 3 to 5 times more dangerous than direct current. The same voltage and current.

Exposure to direct current is more likely to cause a single spastic contraction, which usually removes the subject from the current source.

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For AC and DC, the higher the voltage (V) and amperage (A), the greater the electrical damage (for the same exposure).

Household current in the United States ranges from 110 V (standard power outlet) to 220 V (used for large appliances such as refrigerators and dryers).

High voltage current (> 500 V) tends to cause deep burns, while low voltage current (110 to 220 V) tends to cause muscle twitching and immobility at the current source.

The maximum current that can cause the flexor muscles of the arm to contract but still allow the subject to release the hand from the current source is called the release current.

The relaxation current varies according to body weight and muscle mass.

For an average person weighing 70 kg, the direct current is about 75 milliamps (mA) and the alternating current is about 15 milliamps.

Even when the current is as low as 60-100 mA, the 60 Hz low-voltage alternating current passing through the chest can cause ventricular fibrillation even within a fraction of a second; using direct current, approximately 300-500 mA is required.

If the current reaches the heart directly (for example, through the electrodes of a cardiac catheter or pacemaker), even an amperage of less than 1 mA can cause tremor (AC and DC).

The tissue damage caused by electrical contact is mainly the conversion of electrical energy into heat, causing thermal damage.

The amount of heat dissipation is equal to amperage 2 × resistance × time; therefore, for a given current and duration, the tissue with the highest resistance tends to suffer the most damage. The body's electrical resistance (in ohms/square centimeter) is mainly provided by the skin, because the electrical resistance of all internal tissues (except bones) is negligible.

Skin thickness and dryness increase resistance; dry, well-keratinized and intact skin has an average value of 20 000-30 000 ohm/cm2.

Calluses, thickened palms or plants have a resistance of 2-3 million ohms/cm2; in contrast, thin, moist skin has a resistance of about 500 ohms/cm2.

The resistance of injured skin (such as cuts, abrasions, needle stick wounds) or moist mucous membranes (such as mouth, rectum, vagina) can be as low as 200-300 ohms/cm2.

If the skin resistance is high, more electrical energy can be dissipated through the skin, causing extensive skin burns, but less internal injuries.

If the skin resistance is low, the burn area of ​​the skin is smaller or non-existent, and more electrical energy is transmitted to the internal structure.

Therefore, the absence of external burns does not mean that there is no electrical damage, and the severity of external burns does not indicate the severity of electrical damage.

The damage to internal tissues depends on their resistance and current density (current per unit area; when the same current intensity passes through a smaller area, the energy is more concentrated).

For example, when electrical energy passes through the arm (mainly through low-resistance tissues, such as muscles, blood vessels, and nerves), the current density in the joints increases because a large part of the joint cross-sectional area is composed of high-resistance tissues (such as bones, bones, and nerves). Tendons), reduce the low resistance area of ​​the tissue; therefore, the damage to the low resistance tissue is often more serious in the joint.

The path of current through the body determines which structures are damaged.

Since alternating current constantly reverses direction, the commonly used terms "input" and "output" are inappropriate;'source' and'ground' are more accurate.

The hand is the most common source, followed by the head.

The foot is the most common grounding point. Electric current flowing between the arms or between the arms and feet may pass through the heart, which may cause arrhythmia.

This current is often more dangerous than the current flowing from one foot to the other.

The current flowing to the head can damage the central nervous system.

The electric field strength is the current strength in the area to which it is applied.

Together with the Kouwenhoven factor, it also determines the degree of tissue damage.

For example, distributing a voltage of 20,000 volts (20 kV) on the body of a person about 2 m high will produce a field strength of about 10 kV/m.

Similarly, 110 volts will produce a similar field strength of 11 kV/m when applied to only 1 cm (for example, a child’s lips); this ratio explains why this low-voltage damage can cause some high-voltage Damage to tissues of the same severity.

Conversely, when considering voltage rather than electric field strength, technically speaking, slight or insignificant electrical damage can be classified as high voltage.

For example, when you crawl on the carpet in winter, the electric shock you receive can reach thousands of volts, but the damage caused is completely negligible.

Even if the energy is not enough to cause thermal damage, the action of the electric field can cause damage to the cell membrane (electroporation).

The application of a low-strength electric field can immediately cause an unpleasant sensation ("electric shock"), but rarely causes serious or permanent damage.

The application of high-strength electric fields can cause thermal or electrochemical damage to internal tissues.

High-intensity electric field damage can cause severe edema, and as blood clots in veins and muscles swell, it can lead to compartment syndrome.

Significant edema can also cause hypovolemia and hypotension.

Muscle destruction can lead to rhabdomyolysis and myoglobinuria, as well as electrolyte imbalances.

Myoglobinuria, hypovolemia, and hypotension increase the risk of acute kidney injury.

The consequences of organ dysfunction are not always related to the amount of tissue destroyed (for example, ventricular fibrillation may occur with relatively little tissue destruction).

Even if the current penetrates irregularly into deeper tissues, the burn may be clearly demarcated on the skin.

Due to damage to the central nervous system or muscles, severe involuntary muscle contractions, convulsions, ventricular fibrillation, or respiratory arrest may occur.

Damage to the brain, spinal cord, or peripheral nerves can cause various neurological dysfunctions.

Cardiac arrest may occur without burns, for example when an accident occurs in the bathroom (when a wet person [touching the floor] receives 110 V, such as from a hair dryer or radio).

Children who bit or suck on the power cord may burn their mouth and lips.

This burn can cause cosmetic deformities and affect the growth of teeth, jaws, and jaws.

As many as 10% of children experience bleeding from the labial artery 5-10 days after trauma due to eschar shedding.

Electric shocks can cause violent muscle contractions or falls (such as from a ladder or roof), resulting in dislocations (electric shocks are one of the few causes of posterior shoulder dislocations), spine or other fractures, visceral injuries, and other injuries.

Mild or ambiguous physical, psychological, and neurological sequelae can appear within 1-5 years after injury and cause severe morbidity.

Once the patient is removed from the current, cardiac arrest and respiratory arrest are evaluated.

Perform the necessary resuscitation.

After the initial resuscitation, check the patient from head to toe for trauma, especially if the patient falls or is thrown.

Asymptomatic patients who are not pregnant, have no known heart disease, and are only briefly exposed to household electrical current usually do not have severe acute internal or traumatic injuries and do not require further testing or monitoring.

For other patients, ECG, CBC and formula, myocardial enzyme titration and urinalysis (check myoglobin) should be considered. Patients with loss of consciousness may need a CT scan or MRI.

The first task is to disconnect the patient from the power supply by turning off the power (for example, by tripping or turning off a switch, or disconnecting the device from the power outlet).

High-voltage lines and low-voltage lines are not always easy to distinguish, especially when outdoors.

Note: If you suspect that there is a high-voltage line, to avoid electric shock to rescuers, you should not try to release the patient before disconnecting the power source.

The patient was resuscitated and evaluated at the same time.

Treat shock that may be caused by trauma or very extensive burns.

The formulas used to calculate the fluid required for classic burn resuscitation may underestimate the fluid requirements for electrical burns based on the degree of skin burn; therefore, these formulas are not used.

Instead, titrate the fluid to maintain adequate diuresis (approximately 100 mL/h for adults and 1.5 mL/kg/h for children).

In the case of myoglobinuria, maintaining adequate diuresis is particularly important, and alkalization of urine helps reduce the risk of kidney failure.

Surgical debridement of large amounts of muscle tissue can also help reduce myoglobinuria renal failure.

EV opioids should be used with caution to treat severe pain caused by electric burns.

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Asymptomatic patients who are not pregnant, have no known heart disease, and have only brief exposure to household electricity, usually do not have severe acute internal injuries or trauma that require hospitalization and can be discharged.

Patients with the following conditions need 6-12 hours of cardiac monitoring:

Appropriate tetanus prevention and local treatment of burn wounds are needed.

Treat pain with non-steroidal anti-inflammatory drugs or other analgesics.

All patients with severe burns should be referred to a specialist burn center.

Children with lip burns should be referred to a pediatric orthodontist or maxillofacial surgeon who has experience with these injuries.

Electrical equipment that touches or may come into contact with the body must be properly insulated, grounded, and inserted into a circuit containing a protective circuit breaker.

The life-saving circuit breaker that will trip if even a 5 milliampere (mA) current leak is detected is effective and readily available.

The safety cover can reduce the risk for families with children.

In order to avoid jumping current damage (arc damage), poles and ladders should not be used near high-voltage power lines.

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