Medicina

Burns, Electrical
Introduction

Since its inception in 1849, commercial use of electricity has been one of the most potentially dangerous commodities in our society. According to statistical data, 0.8-1% of accidental deaths are caused by an electric injury, with approximately one quarter caused by natural lightning. Electric injury accounts for 1000 deaths each year in the United States, witha mortality rate of 3-15%.1,2

As the widespread use of electricity and injuries from it increase, all health professionals involved in burn care must appreciate the physiologic and pathologic effects and management of electric current injury. As either the current or its arc causes these injuries, an understanding of some fundamental laws of physics is an essential prerequisite of propermanagement. This article describes the consequences of accidental contact with commercial electric current and delineates principles involved in burn care.

For excellent patient education resources, visit eMedicine's Burns Center. Also, see eMedicine's patient education articles Electric Shock and Thermal (Heat or Fire) Burns.

Physics of Electricity

Electricity is the flow of electrons fromatom to atom.3,4 Movement of electrons is comparable to the way water is passed along in a bucket brigade. Electrons, which comprise the current, are passed along from atom to atom. Amperage is the term used for the rate of flow of electrons. Every time 6.242 x 1015 electrons pass a given point in 1 second, 1 ampere of current has passed. The current is what can kill or hurt a victim of an electricinjury. One ampere is roughly equivalent to the amount of current flowing through a lighted 100-watt light bulb.

In most materials, a number of electrons are free to move about at random until a driving force termed voltage propels them to move in one direction. A large voltage exerts a greater force, which moves more electrons through the wire at a given rate of time. Electric voltage of 380volts or less is considered low voltage and above 380 volts, high voltage. High voltage is generated at the power plant and is transformed down to approximately 120 volts for most wall outlets in homes.

Resistance

Resistance of the human body has been likened to that of a leather bag filled with an electrolyte fluid, with high resistance on the outside and lower inside.5 Skin resistance alsovaries depending on moisture content, thickness, and cleanliness. Resistance offered by the callused palm may reach 1,000,000 ohms/cm2, while the average resistance of dry normal skin is 5000 ohms/cm2. This resistance may decrease to 1000 ohms/cm2 if hands are wet. Skin resistance is encountered primarily in the stratum corneum that serves as an insulator for the body. The voltage gradient in skincannot be increased indefinitely and breaks down at low voltages. Exposure of the skin to 50 volts for 6-7 seconds results in blisters that have a considerably diminished resistance.

The dermis offers low resistance, as do almost all internal tissues except bone, which is a poor conductor of electricity. Other factors that affect the flow of electrons are the nature and size of the substancethrough which it passes. If the atomic structure of the material is such that the force of attraction between its nucleus and outer electrons is small, little force is required to cause electron loss. These substances (eg, copper, silver) in which electrons are loosely bound are termed conductors, because they readily permit the flow of electrons. Materials such as porcelain and glass are composedof atoms that have powerful bonds between their nuclei and the outer electrons. These materials are termed insulators because electron flow is restricted.

Resistance is a measure of how difficult it is for electrons to pass through a material and is expressed in a unit of measurement termed an ohm. The resistance offered to the flow of electricity by any material is directly proportional to...