出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/01/17 22:38:05」(JST)
| Burn | |
|---|---|
| Classification and external resources | |
Second-degree burn of the hand |
|
| ICD-10 | T20–T31 |
| ICD-9 | 940–949 |
| MedlinePlus | 000030 |
| MeSH | D002056 |
A burn is a type of injury to flesh or skin caused by heat, electricity, chemicals, light, radiation or friction.[1][2][3] Most burns affect only the skin (epidermal tissue). Rarely, deeper tissues, such as muscle, bone, and blood vessels can also be injured. Burns may be treated with first aid, in an out-of-hospital setting, or may require more specialized treatment such as those available at specialized burn centers.
Managing burn injuries properly is important because they are common, painful and can result in disfiguring and disabling scarring, amputation of affected parts or death in severe cases. Complications such as shock, infection, multiple organ dysfunction syndrome, electrolyte imbalance and respiratory distress may occur. The treatment of burns may include the removal of dead tissue (debridement), applying dressings to the wound, fluid resuscitation, administering antibiotics, and skin grafting.
While large burns can be fatal, modern treatments developed in the last 60 years have significantly improved the prognosis of such burns, especially in children and young adults.[4][5] In the United States, approximately 1 out of every 25 people with intense, extensive burns will die from their injuries. The majority of these fatalities occur either at the scene or on the way to hospital.[6]
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Burns can be classified by mechanism of injury, depth, extent and associated injuries and comorbidities.
Currently, burns are described according to the depth of injury to the dermis and are loosely classified into first, second, third, and fourth degrees. This system was devised by the French barber-surgeon Ambroise Paré and remains in use today.[7]
It is often difficult to accurately determine the depth of a burn. This is especially so in the case of second degree burns, which can continue to evolve over time. As such, a second-degree partial-thickness burn can progress to a third-degree burn over time even after initial treatment. Distinguishing between the superficial-thickness burn and the partial-thickness burn is important, as the former may heal spontaneously, whereas the latter often requires surgical excision and skin grafting.
The following tables describe degrees of burn injury under this system as well as provide pictorial examples.
| Names | Layers involved | Appearance | Texture | Sensation | Time to healing | Complications | Example |
|---|---|---|---|---|---|---|---|
| First degree | Epidermis | Redness (erythema) | Dry | Painful | 1wk or less | Increased risk to develop skin cancer later in life | |
| Second degree (superficial partial thickness) | Extends into superficial (papillary) dermis | Red with clear blister. Blanches with pressure | Moist | Painful | 2-3wks | Local infection/cellulitis | |
| Second degree (deep partial thickness) | Extends into deep (reticular) dermis | Red-and-white with bloody blisters. Less blanching. | Moist | Painful | Weeks - may progress to third degree | Scarring, contractures (may require excision and skin grafting) | |
| Third degree (full thickness) | Extends through entire dermis | Stiff and white/brown | Dry, leathery | Painless | Requires excision | Scarring, contractures, amputation | |
| Fourth degree | Extends through skin, subcutaneous tissue and into underlying muscle and bone | Black; charred with eschar | Dry | Painless | Requires excision | Amputation, significant functional impairment, possible gangrene, and in some cases death. |
Burns are caused by a wide variety of substances and external sources such as exposure to chemicals, friction, electricity, radiation, and heat.
Most chemicals that cause chemical burns are strong acids or bases.[8] Chemical burns can be caused by corrosive chemical compounds such as sulfuric acid and sodium hydroxide.[9] Hydrofluoric acid can cause damage down to the bone and its burns are sometimes not immediately evident.[10] Chemical burns can be either first, second, or third degree burns, depending on duration of contact, strength of the substance, and other factors.
Electrical burns are caused by either an electric shock or an uncontrolled short circuit (a burn from a hot, electrified heating element is not considered an electrical burn). Common occurrences of electrical burns include workplace injuries, taser wounds, or being defibrillated or cardioverted without a conductive gel. Lightning is also a rare cause of electrical burns.
Since normal physiology involves a vast number of applications of electrical forces, ranging from neuromuscular signaling to coordination of wound healing, biological systems are very vulnerable to application of supraphysiologic electric fields. Some electrocutions produce no external burns at all, as very little current is required to cause fibrillation of the heart muscle. Therefore, even when the injury does not involve any visible tissue damage, electrical shock survivors may experience significant internal injury.[11] The internal injuries sustained may be disproportionate to the size of the burns seen (if any), and the extent of the damage is not always obvious. Such injuries may lead to cardiac arrhythmias, cardiac arrest, and unexpected falls with resultant fractures or dislocations.[12]
The true incidence of electrical burn injury is unknown. In one study of 220 deaths due to electrical injury, 40% of those associated with low-voltage (<500 AC volts) injury demonstrated no skin burns or marks whatsoever. This is sufficient to cause cardiac arrest and ventricular fibrillation but generates relatively low heat energy deposit into skin, thus producing few or no burn marks at all.[13] High voltage electricity, on the other hand, is a common cause of third and fourth degree burns due to the extreme heat yielded by high temperature arcs and flashover associated with voltages over 1000v.
Explosions caused by electrical faults produce high intensity ultraviolet radiation which can also cause radiation burns.
Radiation burns are caused by protracted exposure to UV light (as from the sun), tanning booths, radiation therapy (in people undergoing cancer therapy), sunlamps, radioactive fallout, and X-rays. By far the most common burn associated with radiation is sun exposure, specifically two wavelength ranges of light UVA, and UVB, the latter being more dangerous. Tanning booths also emit these wavelengths and may cause similar damage to the skin such as irritation, redness, swelling, and inflammation. More severe cases of sun burn result in what is known as sun poisoning or "heatstroke". Microwave burns are caused by the thermal effects of microwave radiation.
Scalding (from the Latin word calidus, meaning hot[14]) is caused by hot liquids (water or oil) or gases (steam), most commonly occurring from exposure to high temperature tap water in baths or showers or spilled hot drinks.[15] A so-called immersion scald is created when an extremity is held under the surface of hot water, and is a common form of burn seen in child abuse.[16] A blister is a "bubble" in the skin filled with serous fluid as part of the body's reaction to the heat and the subsequent inflammatory reaction. The blister "roof" is dead and the blister fluid contains toxic inflammatory mediators. Scald burns are more common in children, especially "spill scalds" from hot drinks and bath water scalds.
Generally scald burns are first or second degree burns, but third degree burns can result, especially with prolonged contact.
Steam, smoke, and high temperatures can cause inhalational injury to the airway and/or lungs.[citation needed]
Burn injury results in a local inflammatory response. In larger burns there is a systemic inflammatory response. The lungs may be doubly compromised by smoke inhalation and the venous affluent returning from circulation through the burned skin. Following a major burn injury, heart rate and peripheral vascular resistance increase. This is due to the release of catecholamines from injured tissues, and the relative hypovolemia that occurs from fluid volume shifts. Initially cardiac output decreases. At approximately 24 hours after burn injuries, cardiac output returns to normal if adequate fluid resuscitation has been given. Following this, cardiac output increases to meet the hypermetabolic needs of the body.
The effects of high temperature on tissue include speeding chemical reactions and unfolding (denaturing) proteins. [17]
Heat stimulates pain fibers and alters protein structure in the burn area. Stimulated pain fibers release neuropeptides. Altered proteins activate complements. Complements in turn coat these altered proteins and degranulate mast cells. Complement-coated proteins attract neutrophils which also degranulate to release free radicals and proteases causing further damage. Mast cells upon degranulation release tumor necrosis factor – α (TNF – α, primary cytokine). TNF – α is chemotactic to other inflammatory cells (TNF – α acts as a chemokine in this way) which release secondary cytokines.[18] These secondary cytokines increase permeability of blood vessels in the burn area. This causes exudation of proteins and fluid into the adjacent interstitial tissue. Red cells are not extravasated. This results in increase in the oncotic pressure in the interstitium. The volume of fluid loss is directly proportional to the burn area. If burn area is 10% to 15% of the total body surface area (TBSA), then the consequent fluid loss may cause circulatory shock. If it is more than 25% of TBSA, then inflammation occurs even in the blood vessels remote to the burn, causing greater fluid loss.[18]
In order to determine the need for referral to a specialised burn unit, the American Burn Association devised a classification system to aid in the decision-making process. Under this system, burns can be classified as major, moderate and minor. This is assessed based on a number of factors, including total body surface area (TBSA) burnt, the involvement of specific anatomical zones, age of the person and associated injuries.[6]
Minor burns are:
These burns usually do not require hospitalization.
Moderate burns are defined as:
Persons suffering these burns often need to be hospitalised for burn care.
Major burns are defined as:
These burns typically require referral to a specialised burn treatment center.
Burns can also be assessed in terms of total body surface area (TBSA), which is the percentage affected by partial thickness or full thickness burns. First degree (erythema only, no blisters) burns are not included in this estimation. The rule of nines is used as a quick and useful way to estimate the affected TBSA. More accurate estimation can be made using Lund & Browder charts, which take into account the different proportions of body parts in adults and children.[20] The size of a person's hand print (palm and fingers) is approximately 0.8% of their TBSA, but for quick estimates, medical personnel round this to 1%, slightly overestimating the size of the affected area.[21]
Burns of 10% in children or 15% in adults (or greater) are potentially life threatening injuries (because of the risk of hypovolaemic shock) and should have formal fluid resuscitation and monitoring in a burns unit. Burns units will use surface area to predict severity and mortality, using a methodology such as the Baux score.
The resuscitation and stabilization phase begins with the reassessment of the injured person's airway, breathing and circulatory state. Appropriate interventions should be initiated to stabilize these. This may involve targeted (using specific resuscitation formula to guide fluid administration) fluid resuscitation and, if inhalation injury is suspected, intubation and ventilation or serial assessment using a laryngoscope or similar[citation needed]. Once the injured person is stabilized, attention is turned to the care of the burn wound itself. Until then, it is advisable to cover the burn wound with a clean and dry sheet or dressing (such as cling film).
Early cooling reduces burn depth and pain, but care must be taken as uncontrolled cooling can result in hypothermia.[22]
Children with >10% total body surface area burns, and adults with >15% total body surface area burns need formal fluid resuscitation and monitoring (blood pressure, pulse rate, temperature and urine output).[23] Once the burning process has been stopped, the injured person should be volume resuscitated according to the Parkland formula. This formula calculates the amount of Ringer's lactate required to be administered over the first 24 hours post-burn. Parkland formula: 4mL x (percentage of total body-surface-area sustaining non-superficial burns) x (person's weight in kgs).
Half of this total volume should be administered over the first eight hours, with the remainder given over the following 16 hours. This time frame is calculated from the time at which the burn is sustained, and not the time at which fluid resuscitation is begun. Children also require the addition of maintenance fluid volume. Such injuries can disturb a person's osmotic balance.[24] Inhalation injuries in conjunction with thermal burns initially require up to 40–50% more fluid. The formula is a guide only and infusions must be tailored to the urine output and central venous pressure. Inadequate fluid resuscitation may cause renal failure and death, but over-resuscitation also causes morbidity. Crystalloid fluids appear just as good as colloid fluids and as colloids are more expensive they are not recommended.[25]
Debridement cleaning and then dressings are important aspects of wound care. The wound should then be regularly re-evaluated until it is healed.[3] In the management of first and second degree burns little quality evidence exists to determine which type of dressing should be used.[26] Silver sulfadiazine (Flamazine) is not recommended as it potentially prolongs healing time[26] while biosynthetic dressings may speed healing.[27] There is insufficient evidence to support the use of silver containing dressings.[28]
Intravenous antibiotics may improve survival in those with large and severe burns.[29] However due to the poor quality of the evidence, routine use is not currently recommended.[29]
A number of different options are used for pain management. These include simple analgesics (such as ibuprofen and acetaminophen) and narcotics. A local anesthetic may help in managing pain of minor first-degree and second-degree burns.[30]
Wounds requiring surgical closure with skin grafts or flaps should be dealt with as early as possible.[3] Circumferential burns of digits, limbs or the chest may need urgent surgical release of the burnt skin (escharotomy) to prevent problems with distal circulation or ventilation.[3]
Hyperbaric oxygenation may be useful in adjunct to traditional treatments to speed up healing time; however, more research is needed to confirm or deny this.[31] Honey has been used since ancient times to aid wound healing and may be beneficial in first and second degree burns, but may cause infection.[32]
There are a number of methods to reduce procedural pain and anxiety for people with burns include the use of virtual reality therapy, relaxation techniques, sensory focusing, distraction, and education.[33]
Infection is a major complication of burns. Infection is linked to impaired resistance from disruption of the skin's mechanical integrity and generalized immune suppression. The skin barrier is replaced by eschar. This moist, protein rich avascular environment encourages microbial growth. Migration of immune cells is hampered, and there is a release of intermediaries that impede the immune response. Eschar also restricts distribution of systemically administered antibiotics because of its avascularity.
Risk factors of burn wound infection include:
Burn wounds are prone to tetanus. A tetanus booster shot is required if individual has not been immunized within the last 5 years.
Circumferential burns of extremities may compromise circulation. Elevation of limb may help to prevent dependent edema. An Escharotomy may be required.
Acute Tubular Necrosis of the kidneys can be caused by myoglobin and hemoglobin released from damaged muscles and red blood cells. This is common in electrical burns or crush injuries where adequate fluid resuscitation has not been achieved.
The outcome of any injury or disease depends on three things: the nature of the injury, the nature of the injured or ill person and the treatment available. In terms of injury factors in burns, the prognosis depends primarily on total body surface area percentage burn and the age of the person. The presence of smoke inhalation injury, other significant injuries such as long bone fractures, and serious co-morbidities (heart disease, diabetes, psychiatric illness, suicidal intent etc.) will also adversely influence prognosis. Advances in resuscitation, surgical management, intensive care, control of infection, control of the hyper-metabolic response and rehabilitation have resulted in dramatic improvements in burn mortality and morbidity in the last 60 years. The modified Baux score determines the futility point for major burn injury. The Baux score is determined by adding the size of the burn (% TBSA) to the age of the patient. In most burn units a score of 140 or greater is a non-survivable injury, and comfort care should be offered. In children all burn injuries less than 100% TBSA should be considered a survivable injury.
Following a burn injury children can suffer significant psychological trauma in both the short- and long-term. A major concern of a survivor of any traumatic injury is post-traumatic stress disorder (PTSD). Another significant concern for children is coping with a disturbance in body image.[34]
Disability-adjusted life years for fires per 100,000 inhabitants in 2004.[35]
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no data
< 50
50-100
100-150
150-200
200-250
250-300
|
300-350
350-400
400-450
450-500
500-600
> 600
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As of 2004, 11 million burns requiring medical care occurred worldwide.[36] About 90% of burns occur in the developing world and 70% of these are in children. Survival of injuries greater than 40% total body surface area is rare in the developing world.[37]
An estimated 500,000 burn injuries receive medical treatment yearly in the United States.[7] The 2009 National Burn Repository reports the most common cause of burns as direct fire/flame (43%) followed by scalds (30%). Scald injuries were the predominant cause in children under the age of 5. Burns sustained at home accounted for 65.5% of all burn injuries in the United States that year, and had a mortality rate of 4% overall. This mortality rate was directly associated with advancing age, burn size, the presence of inhalational injury and the female sex.[6] It is estimated that approximately 75% of deaths from burns and fires in the United States occur either at the scene of the incident or en route to medical facilities. Demographically, people sustaining burns in the United States tended to be male (70%) and to have suffered their injuries in a residential setting (43%).[6] The highest incidence of burns occurs in the 18-35yr old age group, while the highest incidence of scalds occurs in children 1-5yrs old and adults over 65.
In India about 700,000 people a year are admitted to hospital for burns, though very few are looked after in specialist burn units.[38]
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| リンク元 | 「I度熱傷」 |
| 関連記事 | 「burning」「bur」「degree」「burn」「first」 |