Electric Shock

Causes thermal injury and/or arrhythmias. The amount of current is the most important determinant of injury (V = IR — current depends on voltage and resistance; wet skin has much lower resistance than dry skin).

Voltage and current

• High voltage injury: >1000 V. Low voltage: <1000 V.
• Current thresholds: 1–3 mA = tingling/pain; 10 mA = muscle contractions; 100 mA is likely to produce VF.

DC current produces a single muscle contraction (high voltage → asystole). AC current produces repeated tetanic contractions — the “can’t let go” phenomenon (high voltage → VF).

The path of current through the body determines injury sites, but this cannot be reliably predicted from entry/exit wound locations alone.

Demographics

Most injuries occur in young males; ~20 deaths/year in Australia. Young children are at particular risk of accidental low-voltage injuries (e.g. chewing cords).

Clinical manifestations

Electrical injuries range from trivial to fatal, whether from lightning or domestic/occupational electric shock.

• Arrhythmias — high-voltage DC causes asystole; high-voltage AC causes VF
• Respiratory arrest — from respiratory muscle paralysis/tetanic contraction
• Neurological — peripheral nerve injury is common; also LOC, weakness, paralysis, respiratory depression, autonomic dysfunction, memory disturbance
• Skin burns — superficial to full-thickness, mainly at the contact and ground sites; entry/exit points are often charred black (all electrical burns are referred to a burn unit — see Burns)
• Deep injury — damage below the skin can be far more severe than surface appearance suggests: muscle necrosis, periosteal burns, compartment syndrome, rhabdomyolysis ± AKI
• Oral injuries — common in children who chew cords; watch for delayed haemorrhage as the eschar separates days later

Examination

Initial assessment follows ALS/BLS: ensure the danger is removed (power off), then response/airway/breathing/circulation.

• Prolonged CPR is warranted — good outcomes are reported even in patients found in initial asystole.
• Examine specifically for skin burns, deep tissue injury (painful), and peripheral neuropathy.

Investigations

• Low-voltage exposure with a normal examination: no further testing needed.
• Higher-voltage exposure, or any abnormal finding: needs ED assessment (risk of compartment syndrome/rhabdomyolysis) — FBC, UEC, CK, ECG (delayed lethal arrhythmias have not been reported in patients without an initial arrhythmia).

Management

• CPR/ALS for patients found down.
• Otherwise: either reassurance/no further management, or ED assessment for deep tissue injury/rhabdomyolysis, fluid resuscitation, and cardiac monitoring as indicated.

From the Emergency Care Institute NSW electrical injuries clinical tool: https://www.aci.health.nsw.gov.au/networks/eci/clinical/clinical-resources/clinical-tools/environmental-health/electrical-injuries