Atlas of pathophysiology, 2 Edition

Part II - Disorders

Skin Disorders

Burns

Burns are the third leading cause of accidental death in the United States.

Causes

·   Thermal: residential fires, automobile accidents, playing with matches, improper handling of firecrackers, scalds caused by kitchen or bathroom accidents

·   Chemical: contact, ingestion, inhalation, or injection of acids, alkalis, or vesicants

·   Electrical: contact with faulty electrical wiring, electrical cords, or high-voltage power lines

·   Friction or abrasion

·   Ultraviolet radiation: sunburn

Pathophysiology

The injuring agent denatures all cellular proteins. Some cells die because of traumatic or ischemic necrosis. Denaturation disrupts collagen cross-links in connective tissue. The consequent abnormal osmotic and hydrostatic pressure gradients force intravascular fluid into interstitial spaces. Cellular injury triggers the release of mediators of inflammation, further contributing to local or systemic increases in capillary permeability.

First-degree burns. Localized injury to or destruction of epidermis by direct (such as chemical spill) or indirect (such as sunlight) contact. This type of burn isn't life-threatening. The barrier function of the skin remains intact.

Second-degree superficial partial-thickness burns. Destruction of epidermis and some of the upper area of the dermis. The barrier function of the skin is lost.

Second-degree deep partial-thickness burns. Destruction of epidermis and more of the dermis.

Third- and fourth-degree burns. Affect every body system and organ. A third-degree burn extends through the epidermis and dermis and into the subcutaneous tissue layer; a fourth-degree burn damages muscle, bone, and interstitial tissues. Within hours, fluids and protein shift from capillary to interstitial spaces, causing edema. An immediate immunologic response to injury makes wound sepsis a potential threat.

Signs and symptoms

·   First-degree burn: localized pain and erythema, usually without blisters in the first 24 hours

·   More severe first-degree burn: chills, headache, localized edema, nausea, vomiting

·   Second-degree superficial partial-thickness burn: thin-walled, fluid-filled blisters that appear within minutes of injury; mild to moderate edema; pain

·   Second-degree deep partial-thickness burn: white, waxy appearance of damaged area, edema, pain (or may be nonpainful)

·   Third- and fourth-degree burns: white, brown, or black leathery tissue; visible thrombosed vessels; no blisters

·   Electrical burn: silver-colored, raised area, usually at the site of electrical contact (damage to underlying tissue can occur even with intact epidermis)

·   Smoke inhalation and pulmonary damage: singed nasal hairs, mucosal burns, voice changes, coughing, wheezing, soot in mouth or nose, darkened sputum

Total burn surface area (BSA) may be estimated quickly using the Rule of Nines, in which an adult patient's body parts are assigned percentages based on the number 9. The Lund-Browder classification allows more precise assessment by assigning specific percentages to an infant or child's body parts and accounts for burn thickness and age differences.

Minor burns

·   Third-degree burns on less than 2% of BSA

·   Second-degree burns on less than 15% of adult BSA (less than 10% in children)

·   All first-degree burns

Moderate burns

·   Third-degree burns on 2% to 10% of BSA

·   Second-degree burns on 15% to 25% of adult BSA (10% to 20% in children)

Major burns

·   Third-degree burns on more than 10% of BSA

·   Second-degree burns on more than 25% of adult BSA (more than 20% in children)

·   Burns of hands, face, feet, or genitalia

·   Burns complicated by fractures or respiratory damage

·   Electrical burns

·   All burns in poor-risk patients

Diagnostic test results

·   Arterial blood gas levels show evidence of smoke inhalation; they may also show decreased alveolar function and hypoxia.

·   Complete blood count reveals decreased hemoglobin level and hematocrit if blood loss occurs.

·   Blood chemistries show abnormal electrolytes caused by fluid losses and shifts, increased blood urea nitrogen with fluid losses, and decreased glucose in children due to limited glycogen storage.

·   Urinalysis shows myoglobinuria and hemoglobinuria.

·   Other blood tests detect increased carboxyhemoglobin.

·   Electrocardiogram shows ischemia, injury, or arrhythmias, especially in electrical burns.

·   Fiber-optic bronchoscopy reveals edema of the airways.

Treatment

·   Minor burns: immersion of burned area in cool water (55 F [12.8 C]) or application of cool compresses

·   Immediate treatment for moderate and major burns: maintain an open airway, endotracheal intubation, 100% oxygen

·   Immediate I.V. therapy to prevent hypovolemic shock and maintain cardiac output (lactated Ringer's solution or a fluid replacement formula; additional I.V. lines may be needed)

·   Partial-thickness burns over 30% of BSA or full-thickness burns over 5% of BSA: cover patient with a clean, dry, sterile bed sheet to help preserve body temperature; don't cover large burns with saline-soaked dressings

·   Debridement followed by application of antimicrobial and nonstick bulky dressing; tetanus prophylaxis if needed

·   Pain or anti-inflammatory medication as needed

·   Major burns: systemic antimicrobial therapy

·   Tetanus toxoid prophylaxis

P.377

CLASSIFICATION OF BURNS BY DEPTH OF INJURY

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Clinical Tip

Estimating the Extent of Burns

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