Wilderness Medicine

Electrical Injury: High-Voltage AC

Background

1. Physics
   • High voltage alternating current (AC): > 600 V
   • Amps = volts/ohm
     • Amperage (current)
     • Directly related to the extent of injury
     • AC is worse than direct current (DC)
     • AC causes tetany with flexors stronger than extensors, so victim grabs wire, causing more injury
   • Resistance
     • Average skin = 5-30 KOhms
     • Moist skin = 1-2 KOhms
     • Body tissue resistance (least to most): nerve, blood, muscle, skin, tendon, fat, bone
2. Risk factors
   • Construction workers working around open power lines, conductors, transformers
   • High voltage without LOC and/or arrest, most common high-voltage injury
3. Morbidity/mortality
   • In US 500-1000 deaths/year due to lightning or electrical burn
   • 3-5% of burn unit admissions are from electrical burns

Pathophysiology

1. Electrons flow abnormally through body causing cell death: leads to: myonecrosis, myoglobinemia, myoglobinuria
2. Produces injury and/or death by depolarizing muscles and nerves; abnormal electrical rhythms in the heart (Vfib) and brain; interferes with respiratory muscles; leads to ischemic brain injury
3. Thermal burns can occur directly from tissue heating or indirectly from burning clothing, etc.
4. Systemic effects
   • Cardiac (10-40%): asystole (esp from lightning), VFib , AFib , SVT
   • Neuro: seizures , coma , amnesia , motor deficits, spinal cord transection
   • Orthopedic: spine and/or scapular fractures, amputation
   • Metabolic: micronecrosis, hyperphosphatemia , acidosis , myoglobinuria, hyperkalemia
   • Vascular: intravascular thrombosis, vasomotor instability

Diagnostics

1. High-voltage AC: > 600 V
   • Duration of exposure can be prolonged
     • Less often than low-voltage AC injuries
   • May be associated with blunt trauma (i.e., fall from power lines)
     • Commonly occur when a conductive object touches an overhead high-voltage power line
     • Categorized identically to low voltage injuries (with or without LOC/arrest)
   • High voltage without LOC and/or arrest
     • Unless the circuit has very high resistance pathway, high voltage injury rarely causes cardiac and/or respiratory arrest
     • Extensive thermal injuries put patient at risk for acute and chronic problems from myoglobinuria
   • High voltage with LOC and/or arrest
     • More unusual presentation high-voltage injuries
     • If circuit crosses the head, LOC and amnesia for the events immediately prior to the injury occur.
2. History
   • Take detailed history from patient
   • If patient unconscious/amnestic for event
     • Take direct history from rescue personnel and/or bystanders
   • Electrical source, electrical type (lightning, low- or high-voltage AC, DC)
   • Duration of exposure to current/injury
   • Specific voltage (if available)
     • Obtain voltage details from power company
3. Symptoms
   • Skin
     • Skin burns , pain, erythema
   • Neurological
     • Seizures , numbness, tingling, weakness, headache , hearing impairment
   • Musculoskeletal
     • Muscle contraction, muscular pain, bone fractures
   • Cardiovascular
     • Heart arrhythmias , cardiac or respiratory arrest , arterial spasm
4. Physical exam
   • Flash or thermal burns
     • Indistinguishable from ordinary thermal burns
     • Do not often have internal electrical component
     • Document as would thermal burns
   • Arc burns
     • Dry parchment center (1mm-several cm diameter) and rim of congestion
     • Identifying these injuries is important in assessing extent of internal damage
   • Contact burns
     • Appearance similar to flash burn
     • Pattern from contacted item visible on skin
     • More limited in size than flash burns
   • Difference between flash and contact burn
     • Full thickness contact burn has unburned hair, flash burn always singes hair
   • Documenting types of burns
     • Arc and contact burns: associated with internal electrical injury, flash burns are not
     • Entrance and exit burns
       • Markers of where circuit traversed body
       • Seen in lightning burns, not AC burns.
       • May denote greater internal damage than is initially evident
5. Diagnostic testing
   • CBC, electrolytes, BUN/Cr, UA
   • (CPK), total (fractionated, if total elevated)
     • Elevated seen in low- and high-voltage injuries, rarely seen in lightning
   • Extensive muscle damage leads to myoglobinemia and myoglobinuria
     • Urine myoglobin if urine hemoglobin +
     • Serum myoglobin if urine hemoglobin +
   • In patient with LOC
     • Consider ABG and tox screen
   • History of chest trauma, SOB, CPR
     • Obtain CXR
   • History of severe trauma, fall from wires
     • Clear C-spine
   • ECG
     • Indicated in any person with suspected electrical injury
     • Most common arrhythmias: A-fib , V-fib , SVT
     • If documented arrhythmias or high-voltage injury: monitoring (tele) indicated
   • EEG: May be indicated in person with LOC or arrest, not critical to early care decision making

Treatment

1. Pre-hospital
   • Instruct EMS to supplement O2 and protect airway in patient with burns above the neck
     • Increased risk of respiratory tract injuries
     • Lightning: If cardiac and/or respiratory arrest, initiate prolonged CPR STAT; patient may recover
   • High voltage: these burns are generally much worse than they appear in ED
   • Treat as a crush injury , not as a burn
     • Extensive deep tissue damage can occur
2. Hospital treatment
   • IV, O2, monitor
   • ACLS and ATLS as needed
   • Hydration (no CNS involvement): IV crystalloid / LR (10 cc/kg/hr) maintain U/O at 1 cc/kg/hr
   • Central access: larger burns, LOC, arrest
   • CNS involvement: Temper hydration vs risk of cerebral edema
   • Myoglobinuria / myoglobinemia:
     • Mannitol 25g IV, THEN 12.5 g q6hr (up to 50-200 g/24hr)
     • Maintain U/O 30-50 cc/hr
     • May consider Lasix : initial dosage: 20-40 mg IV, slowly, dose to maintain U/O 30-50 cc/h
     • Bicarbonate for acidosis and enhanced myoglobin excretion
   • CT for prolonged coma
   • Tetanus prophylaxis
   • Fasciotomy: potentially limb saving
   • May be required for high-voltage burns (compartment syndrome)
   • Urgent surgical/ trauma/ burn consult

Disposition

1. Admit all patients with
   • High-voltage burns
   • Cardiac or neurologic dysfunction, arrhythmias, ECG changes
   • Acidosis, myoglobinuria/myoglobinemia, CPK > 3x normal
   • Large skin burns, or suspected deep tissue burns
   • After stabilization consider transfer to hospital with burn unit
2. Otherwise discharge with follow-up instructions