Electrical Injury is a topic covered in the 5-Minute Emergency Consult.

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Basics

Description

  • Electricity is the flow of electrons through a conductor, across a gradient, from high to low concentration
  • Nature and severity of electrical injuries depend on the voltage, current strength and type, resistance to flow, and duration of contact
  • Ohm law: Voltage (V) = current (I) × resistance (R):
    • Voltage is directly proportional to current and is inversely proportional to resistance.
    • High-voltage (>600 V) and low-voltage sources:
      • Telephone lines: 65 V
      • Household general circuit: 110 V
      • Electrical range or dryer: 220 V
      • Household power lines: 220 V
      • Subway 3rd rail: 600 V
      • Residential trunk line: 7,620 V
      • Industrial electrical power line: 100,000 V
    • Household devices can contain a transformer stepping up a seemingly low-voltage source to high voltage:
      • Microwave, television, computer
    • Resistance (R) is determined by the current's pathway through the body:
      • Nerves, muscles, blood vessels have low resistance and are better electrical conductors than are bone, tendon, fat
      • Water and sweat on skin decrease resistance; calloused skin increases resistance
      • More resistance means less flow, and more conversion to heat
    • Current is measured in amperes (I) and is a measure of the amount of energy flowing through an object:
      • “Let go” current is the max. current a person can grasp and release before muscle tetany inhibits letting go
      • Household general circuit: 15–30 A
      • Tingling sensation/perception: 0.2–2 mA
      • Pain: 1–4 mA
      • Average child “let go” current: 3–5 mA
      • Adult “let go” current: 6–9 mA; higher for men than women
      • Skeletal muscle tetany current: 16–20 mA
      • Respiratory muscle paralysis: 20–50 mA
      • Ventricular fibrillation: 50–120 mA
  • Alternating current (AC):
    • Electron flow rhythmically reverses direction:
      • Homes and offices in US use standard 60 Hz
    • Can produce continuous tetanic muscle contraction, loss of voluntary control of muscles, prolonged contact
    • More dangerous than direct current (DC)
    • More likely to result in ventricular fibrillation at household current level:
      • Stimulation can continue through T-wave period of cardiac cycle
  • DC:
    • Continuous electron flow in 1 direction
      • Defibrillators and pacemakers, industrial sources
    • Large, single muscle spasm tends to throw victim from source:
      • Increased risk of traumatic blunt injuries
      • Shorter duration of exposure
    • More likely to result in asystole
  • Trimodal distribution of electrical injuries:
    • Toddlers (household outlets and cords)
    • Teenagers (risk-taking behavior)
    • Adults (work-related injuries)

Etiology

Types of electrical injury:
  • Direct contact causing tissue destruction:
    • Electrothermal burn may cause skin or deep tissue coagulation necrosis
    • Minor visible injuries may be misleading for extensive deep tissue injury
    • Location of damage is point of contact with source and point of contact with ground
  • Flame:
    • Burns from burning clothing or other substances
  • Electrical arc indirect contact:
    • Burns from the heat of a high-voltage arc (a flash burn) that passes electricity through air
    • May cause thermal and flame burns
    • Flash burns usually result in superficial partial-thickness burns
  • Primary electrical phenomena:
    • Cardiac arrhythmias
    • Muscle contractions and tetany
  • Secondary injury from trauma:
    • Supraphysiologic muscle contraction
    • Fall or being thrown

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Citation

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TY - ELEC T1 - Electrical Injury ID - 307057 Y1 - 2016 PB - 5-Minute Emergency Consult UR - https://emergency.unboundmedicine.com/emergency/view/5-Minute_Emergency_Consult/307057/all/Electrical_Injury ER -