Incision and Drainage

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Chapter 37

Incision and Drainage

Incision and drainage (I&D) procedures in the emergency department (ED) are most commonly performed for soft tissue abscesses (Fig. 37-1).1,2 The total number of ED visits increased from 90 million to 115 million over a 10-year period, with visits for abscess-related complaints increasing faster than overall ED visits.3

The emergence and predominance of methicillin-resistant Staphylococcus aureus (MRSA) as the cause of cutaneous abscesses during the past several decades have necessitated major revisions in long-standing guidelines for antibiotic administration. In light of this significant etiologic change, MRSA should be considered as a probable cause in most skin and soft tissue infections.

Abscess Etiology and Pathogenesis

Localized pyogenic infections may develop in any region of the body. Abscesses generally begin as a localized superficial cellulitis. Some organisms cause necrosis and liquefaction, as well as the accumulation of leukocytes and cellular debris. This is followed by loculation and subsequent walling off of these products, all of which results in the formation of one or more abscesses. Any process or event that causes a breach in the skin’s defensive epithelial barrier increases risk for the development of an abscess. The lymph tissues may be involved in this form of lymphangitis. Systemic signs of toxicity or fever suggest deeper tissue involvement, bacteremia, or both. As the process progresses, the area of liquefaction increases until it “points” and eventually ruptures into the area of least resistance. This may be toward the skin or the mucous membrane, into the surrounding tissues, or into a body cavity. If the abscess is particularly deep seated, spontaneous drainage may occur. In some cases a fistulous tract can arise and lead to the formation of a chronic draining sinus. This development—or the recurrence of an abscess that was previously drained—should broaden the etiologic differential. For example, recurrent abscesses in the perineal or lower abdominal area should raise suspicion for inflammatory bowel disease as the trigger, and recurring abscesses in the axilla or groin should raise the possibility of hidradenitis suppurativa. Chronic abscesses may also be associated with an immunocompromised state. Recurrent abscesses may suggest the possibility of a retained foreign body, underlying osteomyelitis, or the presence of an atypical or drug-resistant organism.

An abscess typically starts as a local superficial cellulitis. Various organisms that colonize normal skin can cause necrosis and liquefaction with subsequent accumulation of leukocytes and cellular debris. Loculation and subsequent walling off of these products lead to abscess formation. The cause of localized abscesses depends on the anatomic location, and they are usually caused by the flora indigenous to that area. Different organisms cause disease based on environmental exposure. For example, direct inoculation of extraneous organisms may occur during a mammalian bite (e.g., Eikenella, Pasteurella), exposure to saltwater (e.g., various Vibrio strains) or freshwater (e.g., Aeromonas), or meat or fish exposure (e.g., Erysipelothrix rhusiopathiae). Pseudomonas folliculitis has been associated with the use of whirlpools.4

Staphylococcal strains, which are normally found on the skin, produce rapid necrosis, early suppuration, and localized infections with large amounts of creamy yellow pus—the typical manifestation of an abscess. Conversely, group A β-hemolytic streptococcal infections tend to spread through tissues and cause a more generalized infection characterized by erythema, edema, a serous exudate, and little or no necrosis—typical manifestations of cellulitis. Anaerobic bacteria, which proliferate in the oral and perineal regions, produce necrosis with profuse brownish, malodorous pus5 and may cause both abscesses and cellulitis.

Normal skin is extremely resistant to bacterial invasion, and few organisms are capable of penetrating intact epidermis. In a normal healthy host with intact skin, the topical application of even very high concentrations of pathogenic bacteria does not result in infection. The requirements for infection usually include a high concentration of pathogenic organisms, such as in hair follicles in the adnexa; occlusion of glands or other structures that prevent desquamation and normal drainage; a moist environment; adequate nutrients; and trauma to the corneal layer, which allows organisms to penetrate into deeper tissues.6 Tissue perfusion may also play a role in the ability to prevent infection. Trauma may be the result of abrasions, shaving, insect bites, hematoma, injection of chemical irritants, incision, or occlusive dressings that macerate the skin. The presence of a foreign body can potentiate skin infections by enabling a lower number of bacteria to establish an infection. For example, abscesses occasionally develop at suture sites in otherwise clean wounds. In addition, abscesses can develop at any site used for body piercing. “High” ear piercings (through the cartilage of the pinna) seem to be at particular risk for infection because of the avascularity of auricular cartilage.7

When favorable factors are present, the normal flora that colonize cutaneous areas flourish and infect the skin and deeper structures. In persons performing manual labor, the arms and the hands are infected most frequently. In women, the axilla and submammary regions are frequently infected because of minor trauma from shaving, contact with garments, a moist environment, and an abundance of bacteria in these areas. Infections may develop anywhere on the body in intravenous (IV) drug users, although the upper extremities are most commonly affected.8,9 Deep soft tissue abscesses can be caused by an addict’s attempts to access deep venous structures when peripheral venous access sites are exhausted.10 In addition, areas with compromised blood supply are more prone to infection because normal host defenses, including cell-mediated immunity, are less available.7

Bacteriology of Cutaneous Abscesses

Although most abscesses contain bacteria, 5% of abscesses are sterile, especially those associated with IV drug use. Clinically, sterile abscesses cannot be differentiated from those caused by bacteria. Somewhat atypical abscesses develop in parenteral drug users. Injection of a cocaine-heroin mixture (“speedball”) may predispose users to abscesses by inducing soft tissue ischemia.11 Bergstein and coworkers9 found anaerobes in 143 of 243 isolates from 57 drug-abusing patients. Abscesses at the site of injection tend to contain predominantly staphylococcal and streptococcal species. However, some drug users lubricate their hypodermic needles with saliva, which potentially explains the isolation of oral pathogens such as Eikenella corrodens from injection site abscesses.

The microbiology and the underlying cause of skin and soft tissue abscesses are related to their location. Abscesses involving the extremities are generally the result of a breach in the skin’s integrity from trauma such as cuts, abrasions, or needle punctures. Abscesses involving the head, neck, and perineal region are usually associated with obstruction of the apocrine sweat glands. These types of abscesses increase in frequency after puberty because of the increased apocrine and sebaceous gland activity. Perirectal abscesses are typically the result of bacterial spread from adjacent anal glands. Vulvovaginal abscesses usually result from obstruction of a Bartholin gland, which then causes duct and gland edema and subsequent infection. Pilonidal abscesses are hypothesized to be caused by sacrococcygeal infections from ingrown hairs in the intergluteal cleft.

In 2002, Brook12 compiled the findings from more than 15 bacteriologic studies of 676 polymicrobial abscesses. S. aureus and group A β-hemolytic streptococci were the most prevalent aerobes in skin and soft tissue abscesses and were isolated in specimens from all body sites. Gastrointestinal and cervical flora (enteric gram-negative bacilli and Bacteroides fragilis) were found most often in intraabdominal, buttock, and leg lesions. Group A β-hemolytic streptococci, pigmented Prevotella, Porphyromonas species, and Fusobacterium species—all normal residents of the oral cavity—were most commonly found in lesions of the mouth, head, neck, and fingers.

In a study of the bacteriology of cutaneous abscesses in children, Brook and Finegold13 found aerobes (staphylococci and group A β-hemolytic streptococci) to be the most common isolates from abscesses of the head, neck, extremities, and trunk, with anaerobes predominating in abscesses of the buttocks and perirectal sites. Mixed aerobic and anaerobic flora was found in the perirectal area, head, fingers, and nail bed. This study noted an unexpectedly high incidence of anaerobes in nonperineal abscesses. Anaerobes were found primarily in areas adjacent to mucosal membranes (e.g., the mouth), where these organisms tend to thrive, and in areas that are easily contaminated (e.g., by sucking fingers, which causes nail bed and finger infections or bite injuries).

If an unexpected or atypical organism is found in an abscess culture, the clinician should consider an underlying process not readily apparent from the history or physical examination. For example, tuberculosis or fungal isolates are sometimes found in immunocompromised patients (e.g., those with diabetes or acquired immunodeficiency syndrome). Finding Escherichia coli suggests an enteric fistula or even self-inoculation of feces in some patients with a psychiatric illness such as Munchausen’s syndrome. Recurrent abscesses without an obvious underlying cause could indicate clandestine drug use. What appears to be a typical recurrent abscess may be a manifestation of an underlying septic joint, osteomyelitis, or rarely, metastatic or primary cancer (Fig. 37-2).

image

Figure 37-2 An abscess that appears in an atypical place or recurs after successful initial treatment should raise the possibility of rare or underlying conditions. A, This patient had a large “abscess” on the lateral chest wall that initially drained unusual gelatinous material, not frank pus. B, At follow-up 3 days later, the abscess was much improved. The contents of the abscess had been sent for pathologic analysis because it had an unusual consistency, and a highly undifferentiated soft tissue malignancy was demonstrated. The fluid was sterile. Normally, analyzing or culturing the contents of an abscess will not yield helpful information, but in this case, the unusual consistency of the collection prompted further analysis. C, This intravenous drug user had an “abscess” of the chest wall drained in various emergency departments several times over a 2-month period, and it seemed to initially respond to drainage and antibiotics. He still had an area of cellulitis, minor fluctuance, and continued drainage near the center of the chest. This is an atypical place for a simple cutaneous abscess. Magnetic resonance imaging demonstrated osteomyelitis and an abscess of the sternoclavicular joint that was draining to the skin and simulating a recurrent cutaneous abscess. He required extensive surgical débridement and prolonged antibiotics. The etiologic organism was never ascertained, but Pseudomonas is often present. D, This patient underwent a sternotomy for bypass surgery a few months ago. She had been treated sporadically for a minor wound infection, but then a draining fluctuant mass developed at the inferior border of the sternum. This is the external manifestation of extensive sternal osteomyelitis.

Special Considerations

Parenteral drug users, insulin-dependent diabetics, hemodialysis patients, cancer patients, transplant recipients, and individuals with acute leukemia have an increased frequency of abscess formation when compared with the general population. At initial evaluation the patient may emphasize an exacerbation of the underlying disease process or an unexplained fever, with symptoms of an abscess being a secondary complaint. In this situation, abscesses tend to have exotic or uncommon bacteriologic or fungal causes and typically respond poorly to therapy.14–17 Patients with diabetes-induced ketoacidosis (DKA) should be evaluated extensively for an infectious process; a rectal examination should be included with the physical examination to rule out a perirectal abscess as the infectious trigger of DKA. This is also true for patients who are immunocompromised. There are several reasons why patients with diabetes and parenteral drug users are at increased risk for abscess formation: intrinsic immune deficiency, an increased incidence of staphylococcal carriage, potentially compromised tissue perfusion, and frequent needle punctures, which allow a mode of entry for pathogenic bacteria.18

Drug users frequently use veins in the neck and in the femoral areas, which can produce abscesses and other infectious complications at these sites.19 Any abscess near a vein of the antecubital fossa or dorsum of the hand should alert the clinician to possible IV drug use; however, substance users may also inject directly into the skin (“skin popping”), which can cause cutaneous abscesses distant from veins (Fig. 37-3).

A foreign body may serve as a nidus for abscess formation. IV drug users frequently break needles off in skin that has been toughened by multiple injections, so the clinician should maintain a high index of suspicion for retained needle fragments. If an abscess is recurrent or if the patient is a known or suspected IV drug user, consider radiographs or other techniques to search for foreign bodies, an underlying septic joint, or osteomyelitis.20 Ultrasound is also a useful adjunct to evaluate for foreign bodies that are not radiopaque.

MRSA

First acknowledged in the 1960s as a cause of infection in patients in health care settings, MRSA has now become the most common identifiable cause of community-acquired skin and soft tissue infections in many metropolitan areas in the United States. The spread of this organism is considered an epidemic, and it is a very virulent and aggressive.21,22

Virulent community-acquired MRSA (CA-MRSA) causes rapid and destructive soft tissue infection because of the presence of two bacterial toxins elaborated by the omnipresent VSA-300 and VSA-400 strains. Panton-Valentine leukocidin enhances tissue necrosis, and phenol-soluble modulin is toxic to neutrophils. A small pustule can become a large abscess in 24 to 48 hours (Fig. 37-4). Such lesions are often mistaken for a spider bite or drug use because of their rapid progression and seemingly spontaneous onset in an otherwise healthy person. Methicillin resistance is mediated by PBP-2a, a penicillin-binding protein encoded by the mecA gene that permits the organism to grow and divide in the presence of methicillin and other β-lactam antibiotics. S. aureus acquires methicillin resistance through a mobile staphylococcal cassette chromosome (SCC) that contains the mecA gene complex (SCCmec). MRSA probably arose as a result of antibiotic selective pressure.23,24

A single clone probably accounted for most MRSA isolates discovered during the 1960s; by 2004, six major MRSA clones had emerged.25 The spread of resistance is thought to be mediated by horizontal transfer of the mecA gene and related regulatory sequences thereon.26

In 1980, the spread of MRSA from hospitals into communities became evident. More recently, community-acquired infections have occurred more frequently, even in people without known risk factors. These observations have led to the identification of some risk factors for CA-MRSA (Box 37-1), including skin trauma (e.g., lacerations, tattoos, IV and intradermal drug use, shaving), incarceration, shared razors or towels, and close contact with others colonized or infected with MRSA.27–35 Animals can also carry MRSA and can function as a source of transmission.36 Importantly, many patients with CA-MRSA have no identifiable risk factors for acquisition of the disease.37

Box 37-1

Risk Factors for Infection with MRSA

MRSA, methicillin-resistant Staphylococcus aureus.

Based on Cohen PR, Grossman ME. Management of cutaneous lesions associated with an emergency epidemic: community-acquired methicillin-resistant Staphylococcus aureus skin infections. J Am Acad Dermatol. 2004;51:132.

CA-MRSA tends to be more virulent than health care–associated MRSA (HA-MRSA) and is associated with more frequent serious complications such as osteomyelitis, joint infections, sepsis, and death. However, these organisms fortunately tend to be susceptible to a broader array of antibiotics.38

The prevalence of MRSA has increased in both health care and community settings. For example, the prevalence of methicillin resistance among S. aureus isolates in intensive care units in the United States was 60%,21 and more than 90,000 invasive infections by MRSA occurred in the United States in 2005.39

HA-MRSA and CA-MRSA differ with respect to their clinical epidemiology and molecular structures.

HA-MRSA is defined as MRSA infection that occurs following hospitalization (hospital onset, formerly “nosocomial”) or MRSA infection that occurs outside the hospital within 12 months of exposure to a health care setting (e.g., history of surgery, hospitalization, dialysis, or residence in a long-term care facility—community onset instead of community acquired).21

HA-MRSA is usually associated with severe, invasive disease, including skin and soft tissue infection, bloodstream infection, and pneumonia.6,40 In fact, S. aureus continues to be a significant cause of surgical site infections.39 HA-MRSA strains tend to be resistant to multiple drugs. MRSA is one of the few pathogens routinely implicated in nearly every type of hospital-acquired infection. This is probably related in part to the organism’s capacity for biofilm formation on indwelling lines and tubes in hospital settings.24

Biofilm facilitates survival and multiplication of MRSA on these surfaces, thereby prolonging the duration of exposure of the organism to antibiotics, as well as promoting the potential for the development of genetic resistance.27

CA-MRSA is defined as MRSA infection that occurs in the absence of health care exposure. It is often associated with skin and soft tissue infections in young, otherwise healthy individuals.27

Most CA-MRSA strains are sensitive to non–β-lactam antibiotics, although a multidrug-resistant isolate has been described in men who have sex with men.41,42 This strain contains the pUSA03 plasmid and carries resistance genes for β-lactams, fluoroquinolones, tetracycline, macrolides, clindamycin, and mupirocin.

The CA-MRSA and HA-MRSA classifications are no longer distinct since MRSA colonization can develop in one realm and manifestations of infection in another. In the mid-2000s in San Francisco, the annual incidence of CA-MRSA surpassed that of HA-MRSA.43

Furthermore, community-onset HA-MRSA infections have been observed with increasing frequency. This was illustrated in a study of 209 patients discharged from hospitalized care; within 18 months following hospital discharge, 49% of new MRSA infections began outside the hospital.44

In another series of 102 patients with CA-MRSA infections, 29% had molecular typing consistent with HA-MRSA.45

CA-MRSA was initially reported in injection drug users in the early 1980s and has since become the most frequent cause of skin and soft tissue infections seen in U.S. EDs and ambulatory clinics. In an assessment of the prevalence of MRSA across the United States, Moran and colleagues46 compiled data from adults who sought treatment of acute skin and soft tissue infections in EDs in 11 American cities in August 2004. S. aureus was isolated from three fourths of the 422 patients who met the study criteria. Seventy-eight percent of the S. aureus isolates were resistant to methicillin. MRSA was isolated from 59% of patients in the study. The prevalence of MRSA ranged from 15% to 74% in the participating EDs (Table 37-1). MRSA was the most common identifiable cause of skin and soft tissue infections in all but one of the EDs.

Frazee and associates,38 reporting from an ED in northern California, found that half of the 137 patients in their study were either infected with or colonized by MRSA. Three fourths of all S. aureus isolates were MRSA. In addition, 76% of cases met a strict clinical definition of CA-MRSA.

The incidence of CA-MRSA, genetically unrelated to nosocomial isolates, increased steadily from 1990 to 2001 and then dramatically in 2002 and each year thereafter.47,48

MRSA has also emerged as a potential sexually transmitted disease. Roberts and colleagues described their treatment of two patients who came to their urban ED with abscesses probably transmitted by heterosexual oral-genital contact. Both tested positive for MRSA.22 A 2010 case report drew a similar conclusion. It reported orogenital transmission of MRSA to an immunocompetent 22-year-old man who tested orally positive for MRSA and group B (genital) Streptococcus after oral contact with a female partner in whom MRSA-positive gluteal lesions had previously been diagnosed.48

In a retrospective chart review, Roberts and colleagues found that 18% of the 524 subcutaneous abscesses treated in their urban ED in 2006 were confined to the genital area. Almost three fourths of the 272 outpatient wound cultures performed on that year’s patient population were positive for MRSA.22

Manifestations of Cutaneous Abscesses

The diagnosis of cutaneous abscess formation is usually straightforward. The presence of a fluctuant mass in an area of induration, erythema, and tenderness is clinical evidence that an abscess exists (see Fig. 37-1). An abscess may appear initially as a definite tender soft tissue mass, but in some cases, a distinct abscess may not be readily evident. If the abscess is deep, as is true of many perirectal, pilonidal, and breast abscesses, the clinician may be misled by the presence of a firm, tender, indurated area without a definite mass. If the findings on physical examination are equivocal, needle aspiration or ultrasound examination may be performed to assist in the diagnosis.49 This approach may also identify a mycotic aneurysm or an inflamed lymph node simulating an abscess. A specific entity commonly mistaken for a discrete abscess is the sublingual cellulitis of Ludwig’s angina (see Chapter 64).

Parenteral injection of illicit drugs can produce simple cutaneous abscesses that unpredictably advance to extensive necrotizing soft tissue infections. The emergency clinician must maintain a high index of suspicion to avoid missing this potentially life-threatening condition.8 Cellulitis and abscess formation can lead to bacteremia and sepsis, especially in immunocompromised patients.

The pain of an abscess often brings the patient to the hospital before it spontaneously ruptures, or the patient can have a draining abscess that appears to have undergone spontaneous rupture and is self-resolving. The patient may have punctured the abscess in an attempt to drain it. In most cases, a formal I&D and packing procedure will be necessary to eliminate the process, even though copious drainage may not be encountered. Although no formal drainage may be required after the spontaneous rupture of a simple cutaneous abscess, conditions such as a perirectal abscess, Bartholin gland abscess, and breast abscess are usually best managed with further drainage and packing.

Imaging

image ULTRASOUND

Cellulitis and Abscesses by Christine Butts, MD

Ultrasound offers a distinct advantage when evaluating a patient with suspected soft tissue infection and may change management. A recent study from Academic Emergency Medicine by Tayal and colleagues evaluated the effect of soft tissue ultrasound on the management of cellulitis in the emergency department.1 The authors found that in patients with a low suspicion for abscess, ultrasound changed management in 56% of cases. Peritonsillar abscesses are difficult to diagnose from the physical examination alone, and some clinicians may feel hesitant to attempt blind drainage. Ultrasound of suspected peritonsillar abscesses has been found to be reliable in making the diagnosis. The overall size of the abscess, as well as its proximity to the carotid artery, can be evaluated with ultrasound, which will perhaps improve the confidence of the clinician in attempting drainage.2,3

General Considerations

Typically, a high-frequency (7.5 to 10 MHz) transducer should be used to evaluate the superficial soft tissues. The higher frequency will allow the clinician sufficient resolution to identify changes consistent with soft tissue infection. The entire area should be scanned in detail, in multiple planes, to identify fluid pockets. Surrounding structures in the area should also be evaluated, especially when incision and drainage are planned. When evaluating the posterior pharynx for a potential paratonsillar abscess, an intracavitary transducer should be used.

Normal Soft Tissue

Normal soft tissue is characterized by well-defined layers, with clear demarcation between these layers (Fig. 37-US1). The top of the screen corresponds to the most superficial soft tissue, including the epidermis and dermis. It should appear hyperechoic (light gray to white), thin, and clearly separate from the underlying layers. Subcutaneous tissue is found beneath the dermis and is of varying thickness. However, as with the most superficial layers, this layer should appear thin and well demarcated from the surrounding layers. Underneath the subcutaneous tissue, muscle will typically be seen as layers of striated tissue separated by bright layers of fascia.

Cellulitis

Cellulitis is recognized on ultrasound by thickening of the skin and subcutaneous layers (Fig. 37-US2). The tissue may also appear more hyperechoic than normal soft tissue. When a significant amount of edema is present within the tissue, bands of hypoechoic (dark gray) or anechoic (black) fluid may be seen within the area of thickened tissue. This is known as “cobblestoning” (Fig. 37-US3). Cobblestoning appears as thin bands of fluid throughout the tissue and can be distinguished from an abscess by the lack of a discrete fluid collection.

Abscess

An abscess is seen as a focal, discrete fluid collection within an area of cellulitis (Fig. 37-US4). The presence of surrounding cellulitis is the key to distinguishing an abscess from other fluid collections such as cysts. The character of the fluid may be variable, depending on the content of the abscess. Collections that are completely fluid will appear as anechoic (black) areas, whereas areas with more solid components will appear to have “internal echoes” within the collections (Fig. 37-US5). Once a focal fluid collection has been located, it can be evaluated in detail to determine the overall size and depth from the surface. Peritonsillar abscesses appear as rounded hypoechoic (dark gray) to anechoic (black) collections of variable size. In addition to confirming the presence of an abscess, the location and depth of the carotid artery can also be judged before an attempt at aspiration.

Ultrasound-Guided Needle Aspiration

Radiologists have performed needle aspiration of abscesses for some time, and emergency clinicians are now becoming more comfortable with the procedure. High-resolution ultrasound technology is being used to obviate “blind” procedures done in the ED (e.g., joint aspiration and central line placement).

For ultrasound-guided drainage of a cutaneous abscess, use a high-resolution probe (5 or 7.5 MHz), and maintain sterility throughout the procedure. Place the sterile transducer over the main body of the abscess, and insert the needle through the skin adjacent to the transducer. Adjust their relative relationships in keeping with the depth and location of the abscess cavity. Guide the needle—seen as a bright artifact—directly into the abscess. Watch the abscess cavity collapse as pus drains out. Scan the entire area of the suspected abscess to capture unexpected extensions. Be sure to drain all pockets.

Laboratory Findings

A complete blood count (CBC), blood cultures, and Gram stain are not standard or required for the treatment of straightforward cutaneous abscesses in the ED. Recommendations for culturing abscesses encountered in the ED are confusing, and clinical practice varies. Firm recommendations for the emergency clinician are difficult to standardize, partly because of insufficient data but also because the recommendations promulgated are not confined to ED abscess treatment. In addition, “complicated” and “uncomplicated” criteria are somewhat arbitrary. Traditionally, culturing the contents of a readily drainable cutaneous abscess was not indicated, nor standard. It simply provided no useful information to the clinician under most circumstances. Many clinicians still forgo routine culturing, even in the CA-MRSA milieu. Currently, there is no agreed on standard concerning routine culturing, and reasonable arguments can be made for a culture or no-culture approach to most abscesses treated in the ED. The authors support selective, not routine culturing but acknowledge that some now consider cultures to be indicated for all abscesses drained in the ED. A culture will potentially identify an unusual or resistant organism, especially if I&D is not curative. Culture will also permit identification of antibiotic susceptibility and assist in customization of antibiotic therapy. Cohort results also provide a framework for local epidemiology and resistance patterns. Culturing the abscess contents will distinguish between MRSA and nonresistant abscesses and will provide useful sensitivity information when managing complicated cases. Culturing should be performed for recurrent, unusual, or atypical abscesses. This information could be useful if the patient responds poorly to initial surgical drainage, if secondary spread of the infection occurs, or if bacteremia develops.50,51 It also appears prudent to obtain cultures from abscesses and other purulent skin and soft tissue infections in patients already taking antibiotics, in immunosuppressed patients, in those with signs of systemic illness, in patients who have not responded adequately to initial treatment, if there is concern for a cluster or outbreak of infection, or in patients with severe local infection.51 Severe local infection can be defined as an abscess larger than 5 cm in diameter, multiple lesions, or extensive surrounding cellulitis. However, the degree of surrounding cellulitis qualifying as “extensive” is ill defined.

When obtaining a specimen for culture, the most accurate and complete culture results will be obtained if one aspirates pus with a needle and syringe before I&D. The material should be cultured for aerobic and anaerobic bacteria. Most clinicians, however, still culture free-flowing purulent material obtained with a cotton swab during I&D. For uncomplicated ED abscesses, this culture technique is standard and adequate to isolate aerobic organisms, including MRSA. A “sterile” culture from a specimen collected with a standard cotton swab after incision is frequently the result of improper anaerobic culture technique. In selected patients, such as immunocompromised hosts or IV drug users, isolation of possible anaerobic organisms by needle aspiration with a syringe through appropriately cleaned (e.g., with chlorhexidine) skin before I&D will enhance the results of culture and can add information that may be clinically relevant to subsequent therapy. There is a general misconception that foul-smelling pus is a result of E. coli. This foul odor is actually caused by the presence of anaerobes; the pus associated with E. coli is odorless.

The discovery of solid or suspicious material in an abscess should prompt histologic evaluation since a malignancy may mimic cutaneous abscesses (see Fig. 37-2A and B).

The majority of patients with an uncomplicated cutaneous abscess will have a normal CBC and will not experience fever, chills, or malaise. Therefore, in the absence of extenuating circumstances, it is not standard to analyze blood from patients with typical cutaneous abscesses because laboratory test results do not lead to a specific therapeutic path. An abscess may produce leukocytosis, depending on the severity and duration of the purulent process; however, the presence or absence of leukocytosis has virtually no diagnostic or therapeutic implications. Bacteremia may occasionally be manifested as a peripheral abscess resulting from septic emboli, and it usually produces clinical characteristics dissimilar to those associated with cutaneous abscesses. A cutaneous abscess itself rarely produces bacteremia.

Gram stain is neither indicated nor standard in the care of uncomplicated simple abscesses. However, patients who appear “toxic” or immunocompromised and those who require prophylactic antibiotics (see the section “Prophylactic Antibiotics” later in this chapter) may benefit from Gram stain in addition to cultures. Gram stain results have been shown to correlate well with subsequent culture results, so in compromised hosts the test can be used to direct the choice of antibiotic therapy. Anaerobic infections should be suspected when multiple organisms are noted on Gram stain, when a foul odor is associated with the purulence, when free air is noted on radiographs of the soft tissue, and when no growth is reported on cultures.12

Indications for and Contraindications to I&D

Surgical I&D is the definitive treatment of a soft tissue abscess52; antibiotics alone are often inadequate. Drainage of a suppurative focus generally results in marked resolution of the symptoms in most uncomplicated cases. In the initial stages, only induration and inflammation may be found in an area destined to produce an abscess. Premature incision, before localization of pus, will not be curative and may theoretically be deleterious because extension of the infectious process and, rarely, bacteremia can result from manipulation. In some cases, the application of heat to an area of inflammation may ease the pain, speed resolution of the cellulitis, and facilitate the localization and accumulation of pus. Nonsurgical methods are not a substitute for surgical drainage and should not be continued for more than 24 to 36 hours before the patient is reevaluated.

Prophylactic and Therapeutic Antibiotic Therapy

The utility of antibiotics remains unproven for prophylaxis against and for treatment of uncomplicated and adequately drained cutaneous abscesses in immunocompetent hosts. For simple abscesses, I&D alone is likely to be quite adequate and curative, even if the causative organism is MRSA. Routine administration of antibiotics after I&D is not currently standard, although the topic is subject to ongoing investigations. Simply stated, drainage alone for uncomplicated abscesses is usually curative.

Furthermore, the use of antibiotics may in fact be harmful. Antibiotic misuse has also been shown to complicate resistance patterns, both in general and in specific patients.

Even though no randomized controlled trial data definitively demonstrate the need for antibiotic therapy in conjunction with I&D of uncomplicated cutaneous abscesses in healthy, immunocompetent patients (without the specific types of valvular heart disease discussed below), there is strong consensus for antibiotic treatment of abscesses associated with the following conditions: severe or extensive disease (e.g., involving multiple sites of infection) or rapid progression in the presence of associated cellulitis, signs and symptoms of systemic illness, associated comorbid conditions, immunosuppression, extremes of age, abscess in an area difficult to drain (e.g., face, hand, and genitalia), associated septic phlebitis, and lesions that are unresponsive to I&D alone.

Antibiotic use is indicated for abscesses with associated severe cellulitis (not well defined and generally a clinical judgement) and those with purulent cellulitis. Purulent cellulitis is defined as cellulitis associated with purulent drainage or exudate in the absence of a drainable abscess. Purulent cellulitis is usually caused by MRSA. Nonpurulent cellulitis, defined as cellulitis with no purulent drainage or exudate and no associated abscess, is usually due to β-hemolytic streptococci. Empirical therapy for MRSA pending culture results is recommended for patients who have failed non-MRSA treatment, for those with a previous history of or risk factors for MRSA, and for those with severe infection or systemic signs and symptoms. Empirical therapy for infection with β-hemolytic streptococci is likely to be unnecessary under these circumstances.

The duration of therapy for skin and soft tissue infections has not been well defined, although no differences in outcome were observed in adult patients with uncomplicated cellulitis receiving 5 versus 10 days of therapy in a randomized, controlled trial.53 In the Food and Drug Administration licensing trials for complicated skin and soft tissue infections, patients were typically treated for 7 to 14 days. However, in the outpatient setting of uncomplicated infections, 3 to 5 days of antibiotic therapy is reasonable but should be individualized on the basis of the patient’s clinical condition and response to treatment. Accordingly, a return wound inspection or primary care follow-up is an important component of the care plan.

IV drug users with an abscess and fever require parenteral antibiotic therapy after blood has been drawn for culture until bacterial endocarditis can be ruled out.50 Additionally, patients who have extensive cellulitis or are clinically septic require immediate IV antibiotics, as well as aggressive surgical drainage of pus. By administering IV ampicillin/sulbactam (2 g/1 g) every 6 hours, Talan and colleagues51 achieved 100% eradication of pathogens from major abscesses in hospitalized IV drug users and non–drug users.

Therapeutic Antibiotics

In contrast to prophylaxis before surgery, the routine use of therapeutic oral antibiotics after I&D of simple cutaneous abscesses in otherwise healthy patients who are not immunocompromised appears to have no value, and their empirical use cannot be scientifically supported. Llera and Levy52 performed a randomized, double-blind study to compare the outcomes of patients treated with a first-generation cephalosporin after the drainage of cutaneous abscesses in the ED with those who received placebo. They found no significant difference in clinical outcome between the two groups and concluded that antibiotics are unnecessary for abscesses in individuals with normal host defenses. This is in agreement with several previous studies.54–56 It should be noted that high-risk patients were often excluded from these studies. Immunocompromised patients have not been adequately studied in this situation and are therefore often given antibiotics empirically, but this practice, though common, has not been supported by rigorous prospective studies.

For empirical coverage of CA-MRSA in outpatients with skin and soft tissue infection, oral antibiotic options include the following: clindamycin, trimethoprim-sulfamethoxazole (TMP-SMX), a tetracycline (doxycycline or minocycline), and linezolid. If coverage of both β-hemolytic streptococci and CA-MRSA is desired, options include the following: clindamyacin alone or the use of TMP-SMX or a tetracycline in combination with a β-lactam (e.g., amoxicillin or cephalexin), or linezolid alone. The use of rifampin as a single agent or as adjunctive therapy for the treatment of skin and soft tissue infections is not recommended.

Facial abscesses should be handled cautiously and checked frequently. Any abscess above the upper lip and below the brow may drain into the cavernous sinus, so manipulation may predispose to septic thrombophlebitis of this system. Treatment with antistaphylococcal antibiotics and warm soaks after I&D has been recommended pending resolution of the process. Areas not in this zone of the face can be treated in a manner similar to that used for other cutaneous abscesses.

A relatively unstudied but a common and currently accepted strategy for patients with soft tissue infections (especially CA-MRSA infections) that are borderline, by clinical judgment, for hospital admission and therapeutic IV antibiotics is to administer a single dose of an IV antibiotic in the ED, followed by oral antibiotics and close outpatient follow-up. When a CA-MRSA infection is likely, IV vancomycin or linezolid is a reasonable option. Oral linezolid may be as effective as the IV form.

Prophylactic Antibiotics

Prophylaxis for Endocarditis

The precise risk for endocarditis after I&D of a cutaneous abscess remains unknown, and it is difficult to predict in which patients an infection will develop and which particular therapeutic procedures subject the patient to the highest risk for infection. However, bacteremia clearly occurs with manipulation of infected tissue, and mortality rates are substantial for MRSA-associated endocarditis (30% to 37%).57,58

Given this risk, it is reasonable that patients at highest risk for cardiac complications related to transient bacteremia be pretreated with appropriate antibiotics within 1 hour preceding the procedure.59–61

Guidelines issued by the American Heart Association (AHA) in 2007 recommend antibiotic prophylaxis for procedures involving the respiratory tract or involving infected skin or musculoskeletal tissue only in patients with cardiac conditions that carry the highest risk for an adverse outcome from infective endocarditis.60 These conditions are listed in Box 37-2. Most skin infections are polymicrobial, but only staphylococci and β-hemolytic streptococci are likely to cause infective endocarditis. Therefore, the therapeutic regimen should include an agent active against these organisms, such as an antistaphylococcal penicillin or a cephalosporin. For patients who cannot tolerate a β-lactam or if MRSA is suspected, vancomycin or clindamycin can be substituted.

Box 37-2

Cardiac Conditions with the Highest Risk for Adverse Outcome from Endocarditis

*Except for the conditions listed previously, antibiotic prophylaxis is no longer recommended for any other form of CHD.

†Prophylaxis is recommended because endothelialization of prosthetic material occurs within 6 months after the procedure.

From Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis. Circulation. 2007;116:1736.

Two clinical situations deserve special mention. First, because of the frequent incidence of valvular damage in IV drug users, prophylactic antibiotics may be indicated before I&D of abscesses in these patients; however, no standards exists. It is prudent to inquire about previous endocarditis or auscultate for a heart murmur if IV drug abuse is suspected or known and administer antibiotics under these circumstances. Second, any patient with a documented history of endocarditis must receive prophylactic antibiotics before the I&D procedure.

Cutaneous abscesses may result from active endocarditis and prophylactic antibiotics may obscure subsequent attempts to identify the causative organism. With this in mind, two or three blood cultures (aerobic and anaerobic) should be considered before antibiotic therapy for those at risk for endocarditis. Patients with a diagnosis of mitral valve prolapse have traditionally been included for treatment with prophylactic antibiotics, but the indication for this is unclear, and antibiotic prophylaxis for uncomplicated mitral valve prolapse is no longer part of the AHA guidelines.62

Kaye63 suggested prophylaxis only for patients who have a holosystolic murmur secondary to mitral valve prolapse.

Prophylaxis for Bacteremia in Other Conditions

Conflicting results have been reported from the few studies investigating the relationship between I&D of cutaneous abscesses and bacteremia. For example, in 1985 Fine and associates64 concluded that I&D of cutaneous abscesses is often accompanied by transient bacteremia. They compared blood culture results from specimens obtained before and at 1, 5, and 20 minutes after I&D procedures in 10 patients with soft tissue infections. None of the cultures of blood obtained before I&D were positive; however, six patients had at least one positive culture after the procedure. Eleven of the 30 postprocedure cultures yielded growth. In contrast, in 1997 Bobrow and coworkers65 concluded that I&D of a localized cutaneous abscess is unlikely to result in transient bacteremia in afebrile adults. Their study included 50 patients with localized cutaneous abscesses. Blood samples were collected before and at 2 and 10 minutes after I&D. In addition, specimens from the wound were collected after drainage. None of the blood cultures were positive, even though 64% of the wound cultures were positive, primarily for S. aureus. Bobrow and coworkers65 noted that prophylactic antibiotics should be given to patients at high risk for bacterial endocarditis. In a discussion of the differences between these findings and those reported by Fine and associates,64 Bobrow and coworkers65 noted that Fine and associates’ cultures were obtained from indwelling, heparinized IV catheters, a practice that allows ample opportunity for contamination. Furthermore, half the patients in Fine’s group had perirectal abscesses, and if these abscesses involved mucosal surfaces, the risk for bacteremia was potentially increased.64

Immunocompromised patients may benefit from the prophylactic administration of antibiotics in preparation for I&D of cutaneous lesions. In contrast to patients with risks for endocarditis, immunocompromised patients are at risk for septicemia secondary to brief bacteremia. IV drug users have a high incidence of diseases associated with human immunodeficiency virus (HIV),61,66,67 and the treating clinician must anticipate various degrees of immunodeficiency among them. Because no specific standard of care exists, clinical judgment must guide the use of antibiotics in these situations.

No specific guidelines have been offered for the antibiotic regimen to be used before I&D of infected cutaneous tissue in patients at risk for conditions other than endocarditis. The choice of antimicrobial agent is based on the organism anticipated to cause the bacteremia. Although the location of the abscess will give some clue to the organism involved, most abscesses contain multiple strains of bacteria. Not all bacteria are potent pathogens, so their mere presence does not predict their role in subsequent morbidity. Because Staphylococcus continues to be the most common cause of cutaneous abscesses, a broad-spectrum antistaphylococcal drug is indicated. Prophylaxis can consist of a single IV dose given half an hour before I&D. A first-generation cephalosporin or penicillinase-resistant penicillin is a good initial choice. Vancomycin may also be considered. Others may prefer cefazolin (Ancef, Kefzol), 1 g intravenously, for adults. This regimen covers staphylococcal and streptococcal species, many gram-negative organisms, and many anaerobes.

Although it has not been studied, it is reasonable to also give antibiotics before I&D to all patients who will subsequently be administered therapeutic antibiotics. The ideal duration of therapeutic antibiotics is unknown. As a general guideline, immunocompromised patients should receive antibiotics for 5 to 7 days and immunocompetent patients for 3 to 5 days after the procedure, depending on the severity of the condition and their clinical response at follow-up.

Recurrent Infections

The first-line approach to the prevention of recurrent soft tissue infections is education regarding personal hygiene and appropriate wound care. Patients should be directed to keep wounds covered with clean, dry bandages. Maintain good personal hygiene with regular bathing and frequent hand washing with soap and water or an alcohol-based hand gel, especially after touching the wound or items that came in contact with the wound. Avoid reusing or sharing personal items that have contacted the infected area.

Environmental hygiene measures should be considered in patients with recurrent skin and soft tissue infections in the household or community setting. Focus cleaning efforts on high-traffic surfaces (i.e., surfaces that come in frequent contact with skin each day, such as counters, door knobs, and toilet seats) that may contact bare skin or uncovered infections.

An approach to individual treatment of recurrent CA-MRSA soft tissue infections is outlined in Box 37-3.

Box 37-3   Strategies to Eradicate CA-MRSA Carrier States in Patients with Recurrent CA-MRSA Soft Tissue Infections

Recurrent community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) soft tissue infections have been linked to a carrier state in affected individuals, with the nose and skin being areas colonized. It may be difficult to totally or permanently eradicate colonization, and there are no proven methods to accomplish this. The following strategies have been used in an attempt to eradicate the carrier state in individuals with recurrent CA-MRSA soft tissue infections. The appropriate time to implement these procedures is not known, but it would be reasonable to institute first-line techniques if more than two to three episodes of proven CA-MRSA infection are documented.

*May cause burning, pruritus, dry membranes, and erythema. Avoid long-term use. Do not substitute bacitracin.

†May cause skin and eye irritation. Apply for 5 minutes and then rinse thoroughly.

‡Do not use rifampin alone since resistance may develop. It can cause an orange color of urine and tears and stain contact lenses. Adjust the dose for patients with renal impairment. Do not use in those with impaired hepatic function.

Oral antimicrobial therapy is recommended for the treatment of active infection only and is not routinely recommended for decolonization. In the case of multiple recurrent infections, consider infectious disease expert consultation.

I&d Procedure

Procedure Setting

Definitive I&D of soft tissue abscesses is performed in either the ED or the operating room (OR). When abscesses are drained in the ED, some centers prefer to use a special area to avoid contamination of general treatment rooms, but protocols vary greatly.

The choice of the locale for the procedure depends on a number of important factors. The location of the abscess may dictate management in the OR. Large abscesses or abscesses located deep in soft tissues require a procedure involving a great degree of patient cooperation, which might be achieved only under general or regional anesthesia. Proximity to major neurovascular structures, such as in the axillae or antecubital fossa, may necessitate specific management. Infections of the hand (with the exception of distal finger infections) have traditionally been managed in the OR because of the many important structures involved and the propensity for limb-threatening complications.

Lack of adequate anesthesia is the most common factor limiting I&D in the ED. The current increased use of ED procedural sedation (see Chapter 33) has changed previous OR cases to ones that can be managed well in the ED. If the clinician believes that the abscess cannot be fully incised and drained because of inadequate anesthesia, the patient should be taken to the OR for management under general anesthesia. In addition to limiting proper drainage, it is inhumane and unethical to subject a patient to extreme pain when alternatives are available.

Equipment and Anesthesia

A standard suture tray provides adequate instruments if a scalpel and packing material are added (Fig. 37-5). Although sterility is impossible during the procedure, one should avoid contamination of surrounding tissue. Some clinicians prefer to use an obligatory skin scrub with an antiseptic solution, but the value of this step is dubious. Most clinician use nonsterile gloves while draining pus, but practice varies.

It is often quite difficult to achieve local anesthesia by direct infiltration because of the poor function of local anesthetic agents in the low pH of infected tissue. Furthermore, distention of sensitive structures by a local injection is quite painful and hence poorly tolerated by most patients. Skin anesthesia is usually possible, but total anesthesia of the abscess cavity itself cannot generally be achieved. If a regional block can be performed (see Chapters 30, 31, and 32), this type of anesthesia is preferred. Alternatively, a field block may be used. It should be noted that infected tissue is very vascular and local anesthetics are therefore absorbed quickly. Strict adherence to maximum safe doses of local anesthetics is required.

The skin over the dome of an abscess is often quite thin, thus making skin anesthesia difficult. If a 25-gauge needle is used carefully, one can frequently inject the dome of the abscess subcutaneously. Without moving the tip of the needle, the anesthetic solution spreads over the dome through the subcutaneous layers into the surrounding skin and provides excellent skin anesthesia. If the needle is in the proper plane (best accomplished by holding the syringe parallel rather than perpendicular to the skin), the surrounding skin blanches symmetrically during infiltration without having to reposition the needle (Fig. 37-6, step 2). In an extremely anxious or uncomfortable patient, judicious use of preoperative sedation (see Chapter 33) with IV opioids and sedatives or with nitrous oxide makes the procedure easier for both the patient and clinician. Ketamine, propofol, or a combination of these drugs is a popular option in the ED setting.

Some clinicians recommend the use of topical ethyl chloride or Fluori-Methane spray for the initial skin incision, but although this is an attractive concept to patients, the pain relief offered by these agents is variable and fleeting. Ethyl chloride is also highly flammable. These vapocoolant sprays may be useful to provide momentary anesthesia for injection of a local anesthetic or for the initial skin incision if the injection or incision is made immediately after blanching of the skin. In general, however, these agents are of minimal benefit as a stand-alone anesthetic agent for all but the smallest of superficial abscesses (e.g., purulent folliculitis).

Incision

One should make all incisions conform with skin creases or natural folds to minimize visible scar formation (Fig. 37-7). Care should be taken in areas such as the groin, the posterior aspect of the knee, the antecubital fossa, and the neck so that vascular and neural structures are not damaged.

A No. 11 or 15 scalpel blade, held perpendicular to the skin, is used to nick the skin over the fluctuant area, and then a simple linear incision is carried the total length of the abscess cavity (see Fig. 37-6, step 3). This will afford more complete drainage and facilitate subsequent breakup of loculations. Attempting to drain an abscess with an inadequate incision is counterproductive and makes packing changes more difficult. A cruciate or X-shaped incision and an elliptical skin excision are to be avoided in the routine treatment of cutaneous abscesses. The tips of the flaps of a cruciate incision may necrose and result in an unsightly scar (Fig. 37-8). A timid “stab” incision may produce pus but is not generally adequate for proper drainage. The scalpel is used only to make the skin incision and is not used deep in the abscess cavity.

Exceptions to the rule regarding aggressive incision are abscesses in cosmetic areas, in areas under significant skin tension (e.g., extensor surfaces), and in areas with extensive scar tissue (e.g., sites of multiple previous drainage procedures). In these special circumstances, a stab incision or simple aspiration alone may be attempted initially, with the goal of limiting tissue injury and resultant scar formation. Use of this less aggressive approach requires that the patient be counseled that multiple decompressions (e.g., via needle aspiration) or delayed aggressive I&D may be required. The abscess will need to be reassessed in 24 to 48 hours to determine whether additional intervention is needed.

Wound Dissection

Following a standard incision, the operator should probe the depth of an abscess to assess its extent and ensure proper drainage by breaking open loculations (see Fig. 37-6, step 5). An ideal instrument for this procedure is a hemostat, optionally wrapped in gauze (or a cotton swab for small abscesses), which is placed into the abscess cavity and spread and manipulated throughout the cavity (Fig. 37-9

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