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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.