Electrical injuries may be caused by exposure to natural lightning, or electricity in the home or workplace. Most injuries involve young males, however accidental injuries can also arise in young children due to contact with power cords.
Injuries can range from trivial to fatal, depending upon the voltage and current involved. Fatalities are just as likely to occur at home as in the workplace, with around 20 Australians dying each year due to electrocution.
Pathophysiology of electrical currents
Electrical currents may cause thermal injury or physiological effects. The amount of current that flows through the body is the most important factor in determining injury – this will depend upon the voltage and resistance (recall V = IR), and is influenced by the following factors.
- Voltage: electrical injuries are arbitrarily divided into high voltage (> 1000V) and low voltage (< 1000 V). Australian household voltage is 240V (which is AC). More severe injuries are seen with higher voltages.
- Type of current: electrical currents may be alternating current (AC) or direct current (DC), with AC being more dangerous than DC. DC results in a single muscle spasm, whilst AC may produce tetanic contractions that prevent the victim from letting go of the source, thereby increasing the duration of exposure.
- Skin resistance has a significant impact upon the severity of an electrical injury. Wet skin has a much lower resistance and hence produces a much higher current.
- Tissue resistance influences the severity and type of injury to different tissues. Nerves have the lowest resistance, then blood vessels, muscles, skin, tendon, fat and bone (ordered from lowest to highest). Tissues with a higher resistance have a tendency to heat up, resulting in thermal injury.
- Current path – for electricity to flow, there must be a completed circuit – this may be completed back to the source itself or by contact with the ground. Damage sustained to the body depends upon the pathway taken and whether the heart is involved – note that trying to predict the pathway based upon entry and exit sites can be unreliable.
Currents around 1-3mA will be felt as tingling or pain, whilst around 10mA will produce muscle contractions. 100mA is likely to cause VF, respiratory arrest and severe burns.
Clinical manifestations of injury
- Arrhythmias and direct myocardial damage – high voltage or DC usually causes asystole, whilst AC usually causes VF. VF is the most common fatal arrhythmia, occurring in up to 60% of patients where the current pathway travels from one hand to the other (i.e. the pathway is transthoracic).
- Respiratory arrest - may result from respiratory muscle paralysis or tetanic contractions.
- Neurological sequelae - may include LOC, weakness, paralysis, respiratory depression, autonomic dysfunction and memory disturbances. Peripheral nerve injuries are common.
- Skin burns may occur, ranging from superficial to full thickness burns. These are most common at the site of electrical contact and places in contact with the ground at time of injury – entry and exit sites are often charred black areas surrounded by oedema and erythema. Secondary flame burns may result if clothing or other combustibles are ignited.
- Damage below the skin may be more severe than it appears, given that bone has the highest resistance and hence produces the greatest amount of heat. This can result in deeper injuries including muscle necrosis, periosteal burns and osteonecrosis. Acute compartment syndromes may result.
- Oral burns in young children can occur from sucking or chewing on extension cords – delayed haemorrhage from the labial artery may occur days later when the eschar separates.
- Massive tissue necrosis may result in rhabdomyolysis and acute kidney injury.
- Patients with a low voltage exposure and unremarkable exam do not need any further testing.
- In other patients, an ECG and blood tests should be done - including FBC, UEC, CK.
- Other tests such as xrays and CT brain depend upon the clinical circumstance – these may be indicated if there is a history of associated trauma, LOC or focal neurological findings.
- Danger is important in this scenario – electrical supply may need to be turned off before touching the patient.
- If required, commence CPR early as VF is the most common rhythm.
- As per usual ACLS guidelines. Prolonged CPR should be undertaken following electrical injury regardless of initial rhythm as most victims are young and good outcomes have been noted even among patients found in asystole.
- Aggressive fluid replacement is often required, especially if extensive burns or signs of muscle necrosis.
- Cardiac monitoring - if abnormal ECG or symptoms such as chest pain.
- Delayed lethal arrhythmias have not been reported in pts without an initial arrhythmia.
- Analgesia - many patients have muscle pain due to tetany.
- Extensive soft tissue damage - management is similar to a crush injury. Ensure adequate fluid resuscitation and good urine output if signs of rhabdomyolysis.
- In pregnant patients, check for fetal harm post electrical shock (low likelihood).
Most patients will be able to be discharged from ED – patients with cardiac arrhythmias or signs of extensive tissue damage will require admission.
Further References and Resources
- Czuczman A, Zane RD (2009) Electrical injuries: A review for the Emergency Clinician. EB Medicine; 11(10)