Epidermis

The outermost layer of the skin is called the stratum corneum. It is composed of dead keratinocytes that are continually sloughing as new ones replace them. In addition to dead cells, the corneum also contains keratin, surface lipids, and dirt. The epidermis does not have any blood vessels.

Dead cells are shed at a fairly constant rate with a process called desquamation. The epidermis also has keratinizing and glandular appendages. Keratinizing appendages develop into hair and nails; glandular appendages include the sweat, scent, and sebaceous glands. The pigment that determines skin color (i.e., melanin) is also found in the epidermis in structures called melanosomes. Manufactured by melanocytes, melanosomes are transported to the keratinocytes and surround them. When skin is exposed to the sun or ultraviolet radiation, the quantity of melanosomes increases, causing a change in skin color.

The innermost layer of epidermis is the stratum basale/germinativum, which contains squamous cells, and is the site of origin for squamous cell carcinoma. Squamous cell cancer is more aggressive than basal cell carcinoma, and often invades surrounding tissues and lymph glands. It is often found on surfaces of the skin which have the most exposure to the sun.

The cells of the lowest, or basal, layer of the epidermis are constantly dividing and producing epidermal cells. Basal cell cancer develops from this layer. It tends to be slow growing, is the most common skin cancer (8 out of 10 cases are basal cell cancer), and has a high rate of recurrence. It is usually found in areas of the body with the most sun exposure.

The granular layer, or stratum granulosum, contains three or four layers of cells. It is composed of cells called keratinocytes, which undergo a maturation process called keratinization. This process produces lipid granules that form waterproof structures and helps in preventing fluid loss and evaporation through the skin into the environment.

Dermis

The dermis, or corium, lies below the epidermis and consists of collagen, elastic, and reticular fibers. It also contains blood vessels, nerves, lymphatics, and smooth muscle.

Hypodermis

The hypodermis functions as a shock absorber and heat insulator. Located under the dermis, it comprises fat, smooth muscle, and adipocytes. These cells store and accumulate necessary fats. The hypodermis acts as a site of energy production, and insulation. This area of the body stores fat in characteristic locations: hips on women, abdomen in men.²

Thermoregulation

Skin, subcutaneous tissue, and fat in the subcutaneous tissue provide heat insulation for the body. Heat is lost from the body to the surroundings by radiation, conduction, convection, and evaporation (Fig. 17-2). Radiation of heat from the body accounts for approximately 60% of the total heat loss. In this mechanism, heat is lost in the form of infrared heat waves. Conduction of heat to objects represents approximately 3% of the total heat loss, whereas conduction of heat to the air represents approximately 15% of the total heat loss. When water is carried away from the skin by air currents, convection of heat occurs. Evaporation constitutes approximately 22% of the heat loss. Even without sweating, water still evaporates from the skin and the lungs; this is called insensible loss and totals approximately 600 mL/day.

FIG. 17-2 Major mechanisms of heat loss from body.

(From Hall JE: Guyton and Hall textbook of medical physiology, ed 12, St. Louis, 2011, Saunders.)

The skin regulates body temperature by conserving heat in a cold environment. Sweating can lower the body temperature in hot environments. The sweat glands are innervated by the sympathetic and parasympathetic nervous systems. When the anterior hypothalamus, in the preoptic area of the brain, is stimulated by excess heat, impulses are sent from this area by way of the autonomic pathways to the spinal cord. From the spinal cord through the sympathetic outflow tracts, the impulses go to the skin all over the body. The sweat glands are innervated by sympathetic nerve fibers. However, in these specific fibers, the neurotransmitter is acetylcholine. Consequently, these fibers are actually sympathetic cholinergic nerve fibers and are stimulated by epinephrine or norepinephrine. Norepinephrine is a catecholamine that is a hormone and neurotransmitter that assists with the fight-or-flight response. It is responsible for cutaneous vasoconstriction and has been associated with the pain of fibromyalgia.³

The sweat gland consists of two portions: a deep subdermal coiled portion that secretes the sweat and a duct portion that conducts the sweat to the skin. Sweat has a pH of 3.8 to 6.5 and contains sodium, chloride, potassium, calcium, lactic acid, and urea; therefore sweating is an act of excretion and secretion.

Protection

The skin protects the body from injurious physical, chemical, electric, thermal, or biologic stimuli. Of particular importance to the perianesthesia nurse is the presence of bacteria on the skin that can cause infection when a patient’s skin barrier is broken. Normal florae of the skin include Staphylococcus, Streptococcus, and Corynebacterium organisms. Diphtheroids are also widely distributed on the skin, especially in moist areas. The normal pH of the skin is 4 to 6.5, resulting from production of lactic acid and residues of amino acids. This slightly acid environment serves a protective mechanism by inhibiting bacterial growth. Diabetic, cardiac, and renal patients tend to have more alkaline skin surfaces, thus being at higher risk for skin infections.⁴

When intact, the skin stops unwanted organisms from entering the body and at the same time prevents the loss of water, electrolytes, and proteins to the external environment. When the skin is broken (e.g., surgical incision, ulceration, abrasion, rash, venipuncture), the barrier between the internal and external environments is broken, which is why aseptic technique is important whenever a break of the skin is anticipated or has occurred.

Standard precautions in the postanesthesia care unit

The Centers for Disease Control and Prevention developed a guideline for preventing transmission of infectious agents in health care settings.⁶ This document is discussed in Chapter 5 with more complete information on the standard precautions in the PACU.

Sterile technique for intravenous therapy

Establishment of an intravenous infusion should be accomplished via sterile technique. The site chosen for venipuncture and cannula (needle) placement should be prepared using aseptic technique according to institutional policies and guidelines. There are many good quality pre-packaged IV prep kits. In general though, all IV preparation includes thorough cleaning of the site with alcohol or Betadine-based preparation solutions, the use of sterile angiocatheters, supplies, and an occlusive dressing over the cannulated site. After the intravenous administration route is established, the cannula should be securely anchored to prevent irritating back-and-forth motion and to avoid potential transport of cutaneous bacteria into the puncture wound.

Burn injuries

A burn, no matter how small, represents a total body assault. The postoperative care of the patient with burn injury can be most challenging to the perianesthesia nurse. These patients usually have a complex array of physiologic complications, from deranged fluid and electrolyte balance to respiratory complications. These patients are also routinely suffering from psychologic problems related to pain, disfigurement, anxiety, and potential permanent lifestyle changes. With their first line of defense against external assaults disrupted, temperature regulation of the burn patient is compromised. It is difficult to maintain normothermia in these patients; the perioperative nurse must take care to prevent burn patients from experiencing hypothermia or hyperthermia. Infection is the most common complication of a burn injury. Meticulous, aseptic skin care is of primary importance. Nursing care of the patient with a burn injury is complex; the reader should refer to Chapter 55 for a discussion of specific pathophysiologic processes, assessment, and nursing interventions for the patient with a burn injury in the PACU.

The four main types of burn injuries include radiation, chemical, electrical, and thermal. A thermal injury can result from extreme cold or heat. Cold (frostbite) and burns are the causes of thermal injury. The most common type of burn injury is the thermal burn caused by excessive heat most commonly from fire, steam, and flammable or hot liquids. Metabolic disturbances and problems in maintenance of thermal control can be challenging. In hospitalized burn patients, mortality can range as high as 25%.

The terms partial thickness, deep, and full thickness are commonly used in the classification of burn injuries. The terms first degree, second degree, third degree, and sometimes fourth degree are based on the degree of destruction, depth, and surface appearance of the burn wound (Fig. 17-3). Ambroise Paré, a French surgeon from the 1500s, developed the burn classification system that is still in use today.

FIG. 17-3 Cross section of skin depicting levels contained in split-thickness and full-thickness skin grafts.

(From Townsend T, et al: The biological basis of modern surgical practice, ed 18, Philadelphia, 2008, Saunders.)

Caustic agents, which can be either acid or base, produce chemical burns. Without immediate, aggressive treatment, these agents can continue to cause further destruction of fascia, fat, muscle, and bone. Electrical burns, which result from direct contact with electric voltage, are deceiving in appearance. Although only the entrance and exit wounds may be visible, massive damage is often sustained as the high-energy sources follow conductive muscle and nerves. This damage may involve cardiac as well as skeletal structures. Arrhythmias, often fatal, can occur. Damage may necessitate amputation of extremities. Thermal injury often occurs in addition to the electric burn from the heat of arcing currents or ignited clothing.

Superficial or first-degree burns damage only the outer layer of skin (epidermis). Partial thickness or second-degree burns injure the outer layer and the layer underneath. Full-thickness or third-degree burns cause severe injury or destruction to the deepest layer of skin, tissues, hair follicles, and sweat glands. A fourth degree burn involves bone, muscle, and often organs. Full-thickness burns are often the least painful, because nerve endings have been destroyed, causing the absence of sensation.

A partial-thickness burn heals without grafting. Grafting is required when part of the skin has been damaged or destroyed, but enough epithelial cells remain in the skin to provide new epidermis. The partial-thickness burn can also be referred to as a first-degree or second-degree burn. Partial-thickness burns can be divided into three categories: (1) superficial burns, in which partial skin loss is seen but no dermal death and therefore no slough; (2) intermediate partial-thickness burn, typically characterized by healing from the level of the hair follicles; and (3) deep partial-thickness burn, which typically heals from the level of the sweat ducts. A deep dermal burn is a partial-thickness burn that can heal without grafting. However, if the burn is complicated by infection or mechanical trauma, it is likely to be converted into a full-thickness burn. Full-thickness, or third-degree, burns cause destruction of all the skin. No viable epithelial elements are present, and destruction of the subcutaneous tissue, muscles, and bones may be seen. The wound must be grafted because the skin will not regenerate.⁷

The effects of burns ranges from redness and a burning sensation to edema, blisters, excruciating pain, debilitating and devastating scarring, shock, and death. Burn patients often require frequent, numerous surgeries to remove dead tissue (debridement), release scarring, and apply split thickness skin grafts or one of the many other applications now available: artificial skin, cultured skin autografts, or collagen-based allograft membranes.⁸ As a result, the perianesthesia nurse may see these patients repeatedly in the preoperative and PACU areas.