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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

- 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

- Large, single muscle spasm tends to throw victim from source: - Increased risk of traumatic blunt injuries - Shorter duration of exposure

- 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

- 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

- 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

- 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

  • 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 VHousehold general circuit: 110 VElectrical range or dryer: 220 VHousehold power lines: 220 VSubway 3rd rail: 600 VResidential trunk line: 7,620 VIndustrial electrical power line: 100,000 VHousehold devices can contain a transformer stepping up a seemingly low-voltage source to high voltage:Microwave, television, computerResistance (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, fatWater and sweat on skin decrease resistance; calloused skin increases resistanceMore resistance means less flow, and more conversion to heatCurrent 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 goHousehold general circuit: 15-30 ATingling sensation/perception: 0.2-2 mAPain: 1-4 mAAverage child "let go"Ł current: 3-5 mAAdult "let go"Ł current: 6-9 mA; higher for men than womenSkeletal muscle tetany current: 16-20 mARespiratory muscle paralysis: 20-50 mAVentricular fibrillation: 50-120 mA
  • Alternating current (AC):Electron flow rhythmically reverses direction:Homes and offices in US use standard 60 HzCan produce continuous tetanic muscle contraction, loss of voluntary control of muscles, prolonged contactMore 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 directionDefibrillators and pacemakers, industrial sourcesLarge, single muscle spasm tends to throw victim from source:Increased risk of traumatic blunt injuriesShorter duration of exposureMore 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 necrosisMinor visible injuries may be misleading for extensive deep tissue injuryLocation 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 airMay cause thermal and flame burnsFlash burns usually result in superficial partial-thickness burns
  • Primary electrical phenomena:Cardiac arrhythmiasMuscle contractions and tetany
  • Secondary injury from trauma:Supraphysiologic muscle contractionFall or being thrown

Diagnosis

Signs and Symptoms

  • Head/neck/ENT:Common entry site for high-voltage injuries:Facial and corneal burnsPerforated tympanic membranesCataracts and optic nerve atrophy may present initially, or delayed 4-6 moIntraocular hemorrhage, uveitisCervical spine injury
  • Cardiovascular:Cardiac arrest, asystole, and ventricular fibrillation are leading causes of deathOther arrhythmias and EKG findings: Sinus tachycardia, atrial fibrillation, premature ventricular contractions, transient ST-elevation, reversible QT-prolongation:Sometimes delayed up to 12 hrUsually resolve spontaneouslyMyocardial damage occurs rarely:Generally epicardial, not transmuralDamage does not follow distribution of coronary arteriesEKG will not show standard injury patterns
  • Respiratory:Brain injury causing respiratory center inhibitionTetanic contraction/paralysis of chest wall/diaphragm muscles:May cause respiratory arrestPostcardiac arrest, respiratory arrestTraumatic lung injuryLung tissue itself appears resistant to electrical injury, probably owing to air content.
  • Neurologic:Respiratory arrestAmnesia, transient confusionLoss of consciousness, altered mental status, seizures, comaSpinal cord injury:May result from blunt trauma or DC effects (hand-to-hand flow)Localized paresis up to/including quadriplegiaLong-term neurologic complications:Seizures, peripheral nerve damage, spinal cord syndromes, psychiatric problems
  • Vascular:Muscle necrosis and compartment syndromesThrombosis in slow-moving venous system owing to coagulationIntimal 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 electrostimulationClassically described injuries:Vertebral column fracturePosterior shoulder dislocationFemoral 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 miscarriageFetal 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 arrestLoss of consciousnessChest painHypoxiaAbnormal EKGDysrhythmia in pre-hospital or ED settingHistory of cardiac diseaseSignificant risk factors for coronary artery diseaseSuspicion of conductive injuryConcomitant 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 exposureProvides baseline renal function, possible presence of hyperkalemia and metabolic acidosis
  • Cardiac markers in:Abnormal EKG or dysrhythmiaHigh-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:
  • 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/hrFoley catheter
  • Evaluate for myoglobinuria and prevent renal failure:Maintain good urine outputIV sodium bicarbonate increases solubility of myoglobin in urineConsider furosemide/mannitolMonitor 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.

See Also (Topic, Algorithm, Electronic Media Element)

  • Burns
  • Lightning Injury
  • Rhabdomyolysis

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)