Pathophysiology

Electricity induced injury can be divided into:

• direct tissue damage
  • results from direct effects of electrical energy
  • can affect cell membranes, abruptly altering their electrical properties (cellular depolarisation) and causing direct cell injury by forming pores in cell membranes (electroporation)
• indirect tissue damage
  • thermal injury
    • caused by conversion of electrical energy into thermal energy as current passes through body tissues.
  • secondary mechanical trauma
    • results from falls or violent muscle contraction (1,2)

Following factors determine the extent of electrical injury:

• magnitude of energy delivered – voltage
  • is the main factor which determine the degree of tissue damage
  • the greater the voltage, the greater the damage
• resistance encountered
  • is the ability to impede the flow of current
  • more resistant tissue generates more heat than less resistant tissue
    • least resistant - nerves, blood, mucous membranes, muscles
    • intermediate resistant - dry skin, tendon, fat tissue
    • most resistant - bone
• type of current
  • alternating current is three times more dangerous than direct current of the same voltage
    • direct current which flows in one direction constantly causes a single muscle contraction often strong enough to force the person away from the current source
    • alternating current, which changes direction periodically, causes a continuing muscle contraction. This will prevent people from releasing their grip from the current source
• current pathway through the body
  • this determines
    • the tissue which are at risk of injury
    • type of injury
    • degree of conversion of electrical injury to thermal energy (irrespective of whether high, low, or lightning voltages are involved)
• duration of contact (2)

Notes:

• an electrical burn predominantly causes damage by the generation of heat. Heat production is proportionate to the electrical energy as determined by the Joule Effect. Also, the rise in temperature of tissue is dependent upon the rate at which heat is conveyed away from the site of injury by conduction, convection and radiation. Consequently, electricity reaching bone tends to heat up this tissue to a greater extent than the surrounding tissue. The greater difficulty of heat dissipation from this site also increases damage
• entry and exit points of electricity to the body are generally the sites where skin has touched the source. Typically the hands or feet, these have a greater skin thickness than other sites. Consequently, the higher resistance makes them prone to greater heat generation with subsequent charring and 'blowout' injuries.
• electricity may arc across the flexion surfaces of the body. The main sites for this phenomenon are the wrist, antecubital fossa and the popliteal fossa
  
  
• electrical injury associated with prolonged skeletal muscle spasm that maintains contact with the source is associated with greater injury due to prolonged exposure. Similarly, muscular spasm can trigger violent body movement with associated trauma. Cardiac arrhythmias are likely if the current is alternating and near the frequency of natural conducting pathways - 40 to 200 cycles per second. Finally, electricity converted to heat may ignite clothing causing a cutaneous burn.

Reference:

• (1) Waldmann V et al. Electrical injury. BMJ. 2017;357:j1418
• (2) Ungureanu M. Electrocutions--treatment strategy (case presentation). J Med Life. 2014;7(4):623-6.