Electrical Injury, Emergency Medicine

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) Ś 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 currents 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"Ł 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"Ł current: 3-5 mA
  - Adult "let go"Ł 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: á

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

Diagnosis

Signs and Symptoms

Head/neck/ENT:
- Common entry site for high-voltage injuries:
  - Facial and corneal burns
  - Perforated tympanic membranes
  - Cataracts and optic nerve atrophy may present initially, or delayed 4-6 mo
  - Intraocular hemorrhage, uveitis
  - Cervical spine injury
Cardiovascular:
- Cardiac arrest, asystole, and ventricular fibrillation are leading causes of death
- Other arrhythmias and EKG findings: Sinus tachycardia, atrial fibrillation, premature ventricular contractions, transient ST-elevation, reversible QT-prolongation:
  - Sometimes delayed up to 12 hr
  - Usually resolve spontaneously
- Myocardial damage occurs rarely:
  - Generally epicardial, not transmural
  - Damage does not follow distribution of coronary arteries
  - EKG will not show standard injury patterns
Respiratory:
- Brain injury causing respiratory center inhibition
- Tetanic contraction/paralysis of chest wall/diaphragm muscles:
  - May cause respiratory arrest
- Postcardiac arrest, respiratory arrest
- Traumatic lung injury
- Lung tissue itself appears resistant to electrical injury, probably owing to air content.
Neurologic:
- Respiratory arrest
- Amnesia, transient confusion
- Loss of consciousness, altered mental status, seizures, coma
- Spinal cord injury:
  - May result from blunt trauma or DC effects (hand-to-hand flow)
  - Localized paresis up to/including quadriplegia
- Long-term neurologic complications:
  - Seizures, peripheral nerve damage, spinal cord syndromes, psychiatric problems
Vascular:
- Muscle necrosis and compartment syndromes
- Thrombosis in slow-moving venous system owing to coagulation
- Intimal injury in fast-moving arterial system may lead to acute or delayed arterial malfunction.
Renal failure secondary to myoglobinuria
Skeletal system/orthopedics:
- Supraphysiologic tetanic muscle contractions from electrostimulation
- Classically described injuries:
  - Vertebral column fracture
  - Posterior shoulder dislocation
  - Femoral neck fracture
Dermatologic:
- Contact/ground wounds: Hands, feet, and head most common and most severe sites
- "Kissing"Ł burns from current exit and re-entry on flexor surfaces

Mouth burn most common <4 yr; sucking/biting on household electrical cord: á

Cosmetic deformity risk if commissure involved
Delayed bleeding (3-5 days) from labial artery when eschar separates
Risk of damage to developing dentition

Fetus much less resistant to electrical shock than mother: á

Obstetric consult or referral for all pregnant patients regardless of symptoms:
- Risk of placental abruption or threatened miscarriage
- Fetal monitoring if >20 wk gestation

History

Determine whether exposure was high or low voltage, the duration and location of contact, or concomitant trauma
If unwitnessed respiratory arrest or ventricular fibrillation in patient, consider electrical injury

Physical Exam
Search the skin for entry/exit wounds and kiss/arch wounds at flexor surfaces á

Essential Workup

Urinalysis for myoglobin
EKG and cardiac enzymes for high-voltage victims, and low-voltage victims with cardiorespiratory complaints
Cardiac monitoring indications:
- Cardiac arrest
- Loss of consciousness
- Chest pain
- Hypoxia
- Abnormal EKG
- Dysrhythmia in pre-hospital or ED setting
- History of cardiac disease
- Significant risk factors for coronary artery disease
- Suspicion of conductive injury
- Concomitant injury severe enough to warrant admission
Prolonged monitoring is probably unnecessary in asymptomatic patients with normal EKG, no dysrhythmias, and exposure to <240 V

Diagnosis Tests & Interpretation

Lab

For most exposures to household current, no testing is indicated:
- Low-voltage burns can still cause dysrhythmias, seizures, and other complications if contact is near the chest or head
Urinalysis for myoglobinuria
Creatinine kinase, electrolytes, BUN, creatinine:
- Positive urine myoglobin and/or high-voltage exposure
- Provides baseline renal function, possible presence of hyperkalemia and metabolic acidosis
Cardiac markers in:
- Abnormal EKG or dysrhythmia
- High-voltage exposures or low-voltage victims with cardiorespiratory complaints

Imaging
Dictated by clinical indications á

Differential Diagnosis

Thermal burns from electrical arcing flash burn vs. deep electrothermal injury
Instability owing to traumatic injuries vs. electrical burns

Treatment

Pre-Hospital

Secure scene; turn off power source for high-voltage incident
Assume traumatic injury in unstable or unconscious patient:
- Spinal immobilization
Standard basic life support/advanced cardiac life support care
Early CPR in postelectric shock arrest may allow time for heart to restart
Splint fractures and dislocations
Cover burns with clean, dry dressings

Care must be exercised at scene to ensure that rescuers do not contact live electrical sources á

Initial Stabilization/Therapy

ABCs
Local wound care for thermal burns
Immobilize/reduce fractures and dislocations

Ed Treatment/Procedures

IV fluid resuscitation:
- Larger fluid volumes may be required owing to extensive 3rd spacing in injured muscle.
- Rapid administration to reach urine output of 1 mL/kg/hr
- Foley catheter
Evaluate for myoglobinuria and prevent renal failure:
- Maintain good urine output
- IV sodium bicarbonate increases solubility of myoglobin in urine
- Consider furosemide/mannitol
- Monitor renal function
Tetanus prophylaxis
Pain control as required

Medication

Bicarbonate: 1 ampule (50 mEq) IV, then add 2 ampules to 1 L of D5W to maintain urine pH >7.45
Furosemide: 0.5 mg/kg IV
Mannitol: 25 g (peds: 0.25-0.5 mg/kg) IV bolus, then 12.5 mg/kg/h IV titrated to urine flow >1 mL/kg/h

Follow-Up

Disposition

Admission Criteria

Documented loss of consciousness
Dysrhythmias, abnormal EKG, or evidence of myocardial damage
Suspicion of deep tissue damage
Myoglobinuria or acidosis
Burn criteria for admit or transfer to burn center
Traumatic injuries requiring admission
Pregnant patients >20 wk gestation

Discharge Criteria

Minor, low-voltage injury (<240 V) with no associated injuries, normal physical exam, and asymptomatic
Cutaneous burns or mild persistent symptoms with normal EKG and no urinary heme pigment
Stable in ED after period of observation
Discharge 1st-trimester patient with threatened miscarriage instructions
Pediatric patients with isolated oral burns and close adult care

Issues for Referral

Burn wound care
Persistence of current symptoms or new delayed symptoms:
- Neurology for delayed weakness, paresthesias
Obstetrics for pregnant patients
Dental or reconstructive surgery for pediatric oral burns

Followup Recommendations

Ophthalmology for delayed cataracts in significant electrical current injuries á

Pearls and Pitfalls

Prolonged cardiac monitoring is probably unnecessary in asymptomatic patients with normal EKG, no dysrhythmias, and exposure to <240 V
With significant electrical burn injuries, administer enough IV fluid to maintain adequate urine output and to stabilize the vital signs:
- Extensive 3rd spacing may occur

Additional Reading

Bailey áB, Gaudreault áP, Thivierge áRL. Cardiac monitoring of high-risk patients after an electrical injury: A prospective multicentre study. Emerg Med J. 2007;24(5):348-352.
Fish áJS, Theman áK, Gomez áM. Diagnosis of long-term sequelae after low-voltage electrical injury. J Burn Care Res. 2012;33(2):199-205.
Spies áC, Trohman áRG. Narrative review: Electrocution and life-threatening electrical injuries. Ann Intern Med. 2006;145(7):531-537.

Codes

ICD9

994.8 Electrocution and nonfatal effects of electric current á

ICD10

T75.4XXA Electrocution, initial encounter á

SNOMED

371708003 Injury due to electrical exposure (disorder)
269431000 Non-fatal electric shock (disorder)
405571006 electrical burn (disorder)
269281006 Nonfatal effect of electric current (disorder)

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