Electrical injuries

Published on 14/03/2015 by admin

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Chapter 31 Electrical injuries

Gordian W.O. Fulde, Christopher J. Mobbs

In a two-year period from 2002, 1493 people in Australia were hospitalised as a result of an electrical injury, including 77 from lightning strikes. Of the 1493, 209 were aged 0–14 years, with 18 of those sustaining injury from high voltage lines.

In a four-year period (2001–2004), there were 162 deaths attributable to electrical injury (93% male), with seven from lightning strikes (all male).

Electrical injuries are more common among males, and mostly occur in the young adult and adult years. The most common locations for injury were, in order, the home and the workplace.

Despite the relative infrequency of these injuries, it is important that health providers be familiar with the types of presentation seen and aware of optimum management techniques.

The sources of electrical injury may be divided into three broad subgroups, with important differences in assessment and management of patients relevant to each. For example, cardiac arrest, as provoked by an electrical current, will more commonly be asystole from a lightning strike and ventricular fibrillation (VF) from a household AC current. The three subgroups, therefore, are:

1. lightning injury
2. high voltage (> 1000 V) electrical injury
3. low voltage (< 1000 V) electrical injury.
Low voltage electrical injury may be further subdivided into patients with or without cardiac and/or respiratory arrest.

PATHOPHYSIOLOGY

Electricity may cause injury via three broad mechanisms:

1. causing direct tissue damage, altering cell membrane resting potential and eliciting muscle tetany
2. conversion of electrical energy into thermal energy, causing tissue destruction and coagulative necrosis
3. traumatic injury resulting from falls or violent muscle contractions.

The site of either direct tissue or thermal energy damage depends on the pathway of current flow.

PHYSICS

Electricity is the flow of electrons from higher to lower potential. Direct current (DC), from sources such as car batteries or defibrillators, flows in one direction. Domestic alternating current (AC) switches to and fro at 50–60 cycles per second (hertz) as this confers advantages in terms of current generation and transmission. Ironically, human muscular tissue is sensitive to frequencies in this range, with tetany of peripheral and VF arrest of cardiac muscles a risk during contact with household electricity. Domestic voltage in Australia is 240 V.

Lightning contains around 10 × 106 V and a current of 10,000–200,000 amperes. However, as a result of the incredibly brief duration (microseconds to milliseconds) of a lightning strike, the final amount of current delivered is much less than expected. It is the electrical current that is important in terms of human morbidity and mortality, and this basic electrical injury potential rests with two laws:

Ohm’s law

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Joule’s law

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So, while dry, thick calloused skin may be more resistant to injury by virtue of its very high resistance (up to 100,000 ohms), the resistance of moist skin is only 1000 ohms. It is therefore of vital importance to preach good electrical safety, especially in the home and workplace, and especially relating to moisture and electrical appliances and the installation of circuit breakers.

Similarly, it is the role of all health professionals to educate the public about safety during electrical storms. Those who enjoy outdoor recreation, such as golfers and hikers, are the major group of people affected by lightning strike. Solo people who are struck make up 70% of the recorded mortality. Most fatalities (about 70%) are recorded between midday and 6 pm.

Deaths occur five times more frequently in the country than in urban areas. The summer storm season is associated with the highest mortality. The annual mortality is decreasing in all recording countries.

Three major predictors of mortality are: cardiac arrest at the time of injury, cranial burns (5-fold increase) and leg burns.

In order to avoid lightning there are some simple measures which should be followed:

• Stay indoors during a storm, or seek shelter in a building or car (not a convertible).
• Avoid contact with any metal such as golf clubs, umbrellas, tent poles, gates, roofs or hair clips.
• Do not stand next to or under the tallest object in sight, such as a tree, pole or haystack.
• Avoid being in a group—split up so that someone can call for help if necessary; give CPR.
• Do not stand with your feet apart, as this increases your stride potential and can result in major burns.
• If caught alone, the correct procedure is to curl up on the ground, preferably in a ditch, well away from higher objects.

It is important to note that, contrary to popular belief, lightning does strike twice or more in the same spot.

Wide-band magnetic direction finders are increasingly used to warn of incoming lightning storms.

Lightning injuries can be markedly decreased by taking measures to avoid becoming a conductor, and by not being near an obvious conductor. Piloerection during an electrical storm can mean that a lightning strike is imminent, and immediate evasive measures along the lines of those described above should be taken.

LOW AND HIGH VOLTAGE ELECTRICAL INJURY

The type and amount of current can be inferred from the nature of the source. Electricians and other tradespeople may be able to give accurate information as to strength of power source and current type. However, within appliances conversions from the more dangerous AC to DC, and to a different voltage, are possible. Entry and exit wounds may be visible, but their absence does not rule out serious injury and they may give no indication as to severity of underlying organ damage. The current between any such wounds does not necessarily travel in straight lines.

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