Download Electrical Burns

Electrical Burns
Physics
 Joule heating – passage of electrical current through body resulting in conversion
to heat
o Power = Voltage x Current
o Current = Voltage/Resistance
o Thus
 Heat = Current2 x Resistance x Time of contact
 Contact with high-voltage current may be associated with an arc or light flash.
 An electric arc is formed between two bodies of sufficiently different potential
(high-voltage power source and the body, which is grounded).
 Temperature of the ionized particles and immediately surrounding gases of the arc
can be as high as 4000°C (7232°F) and can melt bone and volatilize metal.
 As a general guide, arcing amounts to several centimeters for each 10,000 volts.
 Skin resistance varies depending on moisture content, thickness, and cleanliness.
Resistance offered by the callused palm may reach 1,000,000 ohms/cm2, while the
average resistance of dry normal skin is 5000 ohms/cm2. This resistance may
decrease to 1000 ohms/cm2 if hands are wet.
Pathophysiology
 Effects of electricity on the body are determined by
1) type of current,
2) amount of current
3) pathway of current
4) duration of contact
5) area of contact
6) resistance of the body
7) voltage.
 Electrical burns causes damage by
1. Direct current
i. Joule heating
 current generated heating with resultant thermal burn
 Thermal tissue damage results from heat generated as current is
conducted through the tissues.
 Although individual tissues have different resistances; bone
(highest), fat, tendon, skin, muscle, blood vessels and nerve (least),
tissues act in combination as a single, uniform resistor
 deep tissues with high resistance, such as bone retain heat and
conduct it to adjacent tissues such as muscle and periosteum,
sustaining greater damage when compared to overlying skin
ii. Electroporation
 cell membrane damage secondary to increased trans-membrane
potentials induced by strong electric fields, resulting in cell death.
 Larger cells (muscle and nerve) are most vulnerable to membrane
breakdown – explains significant skeletal muscle necrosis in the
absence of visible thermal changes.
2. Thermal burn
i. Arc/Flash burn
ii. Clothes cathing alight
3. Tetanic muscular contractions
i. lock-on phenomenon
 Alternating current is more dangerous than direct current as it
causes tetanic contraction, which accounts for the ‘lock-on’
phenomenon—contraction of the flexors preventing release of the
electric source and prolonging exposure with increased tissue
damage
ii. suffocation
iii. falls
 In high-voltage accidents, the victims usually do not continue to
grasp the conductor. Often, they are thrown away from the electric
circuit, which leads to traumatic injuries (eg, fracture, brain
hemorrhage)
 High voltage injury is defined as >1000V
 In high voltage injuries the body acts as a conductor rather than a resistor.
 Cross-sectional area is indirectly related to the tissue damage such that the smaller
the cross-sectional area across which current travels, the greater the injury.
 Limbs conduct more electricity than the thorax.
 Joints, in particular, have a small cross-sectional area and a high proportion
of high resistance bone. Therefore Ohms law would predict higher passage of
current and heat production
 High voltage injury have multisystem consequences
Cardiac
Arythmias, cardiac arrest
Respiratory
Respiratory arrest—central or due to muscle paralysis
Renal
Myoglobinuria—renal failure
Neurological
Loss of consciousness, transient paraplegia, peripheral neuropathy
Fractures
Secondary to muscle spasm/falls
Skin
Cutaneous burns
Other—long-term
Cataracts, neuropsychological problems
Management
First Aid
 Turn off power source
 If unable to do this - wearing lineman's gloves, trained electricians must separate
the victim from the circuit by a specially insulated pole. Looping a polydacron
rope around the injured patient is another method of pulling him or her from the
electric power source. Ideally, the first responder should stand on a dry surface
during the rescue.
 Commence resuscitation
o Once current is stopped, patient should breathe as medullary centers usually
not affected by current path (arm-arm or arm-leg)
o ventricular fibrillation may be induced wheb current flow increases above 3040 mA
Low Voltage injury
 Usually involves hand or mouth in children
 Treatment of oral cavity electric burns
o Clean electric burn wound of the oral cavity and then treat with a petroleum
base antibiotic ointment 4 times a day.
o apply arm splints to keep the child's hands away from his or her mouth.
o Administer feedings through a catheter bulb syringe to limit trauma to the
injured area.
o Tetanus immunoprophylaxis is mandatory for patients with a tetanus-prone
wound.
o Systemic antibiotic therapy has no apparent therapeutic benefit.
o Delayed hemorrhage from the labial artery is noted in as many as 24% of
patients. Bleeding can occur at any time from the day of injury to 221 days
later. In most cases, bleeding can be controlled easily with manual pressure;
however, ligation of the bleeding vessel is occasionally required. When these
patients are discharged from the hospital, instruct their parents on how to
manage delayed bleeding by direct application of pressure.
 Definitive treatment of electric burns
o remains controversial.
o Four different treatment plans have been proposed either to prevent or correct
the deformity.
i. Immediate excision within 12 hours after injury has been recommended
to shorten the period of wound repair and to permit restoration with
minimal reconstructive procedures.
ii. Delayed primary reconstruction, 4-7 days after injury when the extent of
tissue necrosis is known, also has been suggested.
iii. Delayed reconstruction following complete healing of the wound is
another approach.
iv. immediate postburn splinting also has been advocated to avoid surgical
reconstruction.
o General consensus
 splinting of the mouth after acute edema resolves, often 5-12 days after
injury.
 Splinting should continue until the scar softens and loses its contractile
potential, which usually takes 6-12 months.
 perform surgical revision to correct residual deformity.
High Voltage Injury
 Low-voltage current generally follows the path of least resistance (ie, nerves, blood
vessels), yet high-voltage current takes a direct path between entrance and ground.
 The volume of soft tissue through which current flows behaves as a single uniform
conductor, thus is a more important determinant of tissue injury than the internal
resistance of the individual tissues.
 Current is concentrated at its entrance to the body, then diverges centrally, and
finally converges before exiting. Consequently, the most severe damage to the
tissue occurs at the sites of contact, which are commonly referred to as the entrance
and exit wounds.
 High-voltage electric entry wounds are charred, centrally depressed, and leathery
in appearance, while exit wounds are more likely to “explode” as the charge exits.
High-voltage electrical burns often leave a black metallic coating on the skin that is
mistaken for eschar, from vaporization of the metal contacts and electroplating of
the conductive skin surface. Cleansing of the coating usually reveals only
superficial skin injury.
 Electric current chooses the shortest path between the contact points and involves
the vital structures in its pathway.
 Fatalities are high, nearly 60% in hand-to-hand current passages, and are
considerably lower in hand-to-foot current passages (20%). Severity of damage to
the tissue is greatest around the contact sites.
 Consequently, anatomic locations of the contact sites are critical determinants of
injury. Most of this underlying tissue damage, especially muscle, occurs at the time
of initial insult and does not appear to be progressive.
 Microscopic studies of electric burns demonstrate that this initial destruction of
tissues is not uniform. Areas of total thermal destruction are mixed with apparently
viable tissue.
 Low threshold for fasciotomies - necrosis of the entire limb is the most serious
complication, necessitating amputation usually within 2-3 days after injury.
Fluid Resuscitation
 The quantity of fluid sequestered in the injured tissue usually cannot be estimated
using skin surface measurement, because the magnitude of damage to the
underlying tissue often is grossly underestimated.
 Consequently, titrate the quantity of fluid administration to maintain an adequate
urinary output.
 In contrast to flame injury, completion of fluid resuscitation can be predicted by
the patient's hematocrit and plasma volume. When extracellular fluid is restored,
the hematocrit and plasma volume will return to normal if significant
hemolysis has not occurred.
 In acute electric injuries in the adult with underlying devitalized tissue, administer
Ringer lactate solution without glucose at a rate sufficient to maintain a urinary
output of 50-100 mL/h.
 In the presence of hemochromogens in the urine, the rate of fluid infused must be
sufficient to maintain a minimum urinary output of 100 mL/h. This rate and
volume of fluid administration is continued until the urine is free of pigment.
Alkalization of the urine by adding sodium bicarbonate to the IV fluid increases
the solubility and clearance rate of myoglobin in the urine.
 Use of Dextran has been proposed as a method of sealing the pores in the damaged
membranes although is not routinely used in high voltage electrical injury
management
Assessment of extent of tissue damage
 After resuscitation and stabilisation, xenon 133 and Tc99 scans have been shown
to be accurate predictors of tissue viability
 MRI scans alone have shown poor sensitivity. Gadolinium increases sensitivity of
areas of tissue oedema
Early Operative management
Complications
1. Peripheral nerve injury
a. may be involved by direct injury at the site of entrance or exit or in
polyneuritic syndrome involving nerves far removed from the points of
contact.
b. Typical symptoms include numbness (anesthesia) and “pins and needles”
sensation (paresthesia).
c. Loss of function in a peripheral nerve is usually transient, and complete
recovery may be expected if the nerve is not involved in local tissue
injury; however, permanent damage to peripheral nerves in electric injuries is
limited to the area of local tissue contact.
d. Median, ulnar, and radial nerves have the highest incidence of persistent
dysfunction.
e. A late cause of reversible peripheral nerve injury may be secondary to
heterotopic bone formation, which most often occurs at the elbow, resulting
in ulnar nerve dysfunction.
2. Central nerve injury
a. acute and delayed spinal cord injuries have been described distal to the site of
electric contact - spinal atrophic paralysis
b. prognosis is unfavourable
3. Scalp burns
a. Classification:
i. burns without direct bone involvement
ii. burns with direct bone involvement (outer table only or both tables)
iii. burns involving dura mater
iv. burns involving the brain.
b. Devitalised bone has been left –insitu as a bone graft and skin over closed with
a flap.