Skin and Soft Tissue Infections - Incision, Drainage, and Debridement

Skin and soft-tissue infections (SSTIs), which include infections of skin, subcutaneous tissue, fascia, and muscle, encompass a wide spectrum of clinical presentations, ranging from simple cellulitis to rapidly progressive necrotizing fasciitis. Diagnosing the exact extent of the disease is critical for successful management of a patient of soft-tissue infection.[1, 2, 3, 4, 5]

The various types of SSTIs, listed according to clinical presentation and anatomic location, include the following:

• Impetigo

• Folliculitis

• Furuncles

• Carbuncles

• Erysipelas

• Cellulitis

• Necrotizing fasciitis, also known as hemolytic streptococcal gangrene, Meleney ulcer, synergistic gangrene, and Fournier gangrene (when localized to the scrotum and perineal area)

• Pyomyositis

SSTIs may be caused by any of a formidable number of pathogenic microorganisms, and they may be either monomicrobial or polymicrobial. The following are the most important pathogens:

• Staphylococcus aureus (the most common pathogen)

• Streptococcus pyogenes

• Site-specific infections - Indigenous organisms (eg, gram-negative bacilli in perianal abscesses)

• Immunocompromised hosts and complicated SSTIs - Multiple organisms or uncommon organisms (eg, Pseudomonas aeruginosa, beta-hemolytic streptococci, Enterococcus)

• Polymicrobial necrotizing fasciitis - Mixed infection with both aerobes (eg, streptococci, staphylococci, or aerobic gram-negative bacilli) and anaerobes (eg, Peptostreptococcus, Bacteroides, or Clostridium)

• Monomicrobial necrotizing fasciitis: S pyogenes

Classification of SSTIs

For the purposes of this article, SSTI may be divided into the following categories:

• Uncomplicated SSTI

• Nonnecrotizing complicated SSTI

• Necrotizing fasciitis

Uncomplicated SSTIs include superficial cellulitis, folliculitis, furunculosis, simple abscesses, and minor wound infections. These infections respond well to either source control management (ie, drainage or debridement) or a simple course of antibiotics. These infections pose little risk to life and limb.

Complicated SSTIs involve the invasion of deeper tissues and typically require significant surgical intervention. The response to therapy is often complicated by underlying disease states. Complicated SSTIs include complicated abscesses, infected burn wounds, infected ulcers, infections in diabetics, and deep-space wound infections. They are often limb- or life-threatening.

Necrotizing fasciitis is a progressive, rapidly spreading, inflammatory infection that is located in the deep fascia and is associated with secondary necrosis of the subcutaneous tissues. The inflammation of the deep fascia causes thrombosis of the dermal vessels, and it is this thrombosis that is responsible for the secondary necrosis of the overlying subcutaneous tissue and skin.

It is imperative to distinguish necrotizing infections from nonnecrotizing infections. Early diagnosis and intervention may save a life; delayed diagnosis and treatment may lead to loss of a limb or a life.

Predisposing factors

Factors predisposing to the development of SSTIs include the following:

• Breach in the epidermis

• Dry and irritated skin

• Immunocompromised status - Malnutrition, hypoproteinemia, burns, diabetes mellitus, AIDS

• Chronic venous insufficiency

• Chronic lymphatic insufficiency

• Chronic neuropathy

Any abscess, however small, must be drained for complete resolution. Any ulcer covered with dead and necrotic tissue must be debrided to promote growth of healthy granulation tissue and healing. Necrotizing fasciitis is a surgical emergency; early surgical treatment optimizes outcomes for these patients.

There are no absolute contraindications for incision, drainage, and debridement of SSTIs. If the patient's physical condition is compromised, stabilization to render him or her fit for anesthesia should be carried out before these procedures are undertaken.

In the drainage of an abscess, the incision should be made at the point of maximal fluctuance. If possible, it should be made in a dependent area; however, a dependent incision should not be made if a tubercular etiology is suspected. Ideally, the direction of the incision should be in line with the natural skin crease.

A bold incision must be made that goes all the way into the abscess cavity. However, if there are any major vessels or nerves in the area, additional care should be taken in making the incision, and blunt dissection should be used instead to enter the abscess cavity. Any necrosed or unhealthy skin on the roof of the abscess should be excised completely.

Debridement should be done until healthy dermal bleeding is seen on the edges of the skin. There should be no loose undermined skin edges at the end of surgical debridement. However, overzealous debridement should be avoided in nonnecrotizing SSTIs; a staged debridement should be planned to minimize damage to healthy tissue.

Consent should be obtained from the patient or family member, when appropriate.[6] The reason the procedure is being performed (suspected diagnosis); the risks, benefits, and alternatives of the procedure; the risks and benefits of the alternative procedure; and the risks and benefits of not undergoing the procedure. Allow the patient the opportunity to ask any questions and address any concerns they may have. Make sure that they have an understanding about the procedure so they can make an informed decision.

The patient should be counseled about the risks of bleeding (damage to adjacent blood vessels), dissemination of infection (sepsis, endocarditis), and injury of local nerves.

The patient should also be counseled that even if there are no complications, the procedure may not be successful (the abscess may not be completely drained, additional surgery may be necessary).

Discuss how these risks can be avoided or prevented (eg, adequate analgesia, use of ultrasound when possible or indicated, use of antibiotics when indicated).

Controlling the source of infection is the key to management of skin and soft-tissue infections (SSTIs) because it is the fastest way of decreasing the bacterial load.[7] Source control is achieved by means of pus drainage and debridement (see Technique). The aim of debridement is to create an acute wound milieu so as to trigger the body’s natural wound healing mechanisms and thereby promote healing.

In addition to surgical management of an SSTI, selected investigations, antibiotic therapy, or both may be indicated.

Laboratory tests

Patients with uncomplicated SSTIs usually do not require any investigations and need not be hospitalized. However, immunocompromised patients or those with symptoms and signs of systemic toxicity, such as tachycardia and hypotension, may require the following tests:

• Wound culture

• Blood culture and drug susceptibility

• Complete blood cell (CBC) count with differential

• Creatinine level

• Bicarbonate level

• Creatine phosphokinase level

• C-reactive protein level

Additional investigations may be indicated, depending on the severity of systemic toxicity.

Antimicrobial therapy

Uncomplicated SSTIs with no symptoms or signs of systemic involvement respond well to incision and drainage and appropriate wound care. Patients with relatively small abscesses usually do not require any antibiotics. However, evidence has shown that even in the absence of associated cellulitis, antibiotics may hasten the resolution of an abscess after drainage, so this should be considered in larger abscesses or those with significant associated inflammation. The extent of abscess must be confirmed and complete drainage ensured at the time of surgical exploration.

In the setting of systemic disease or an immunocompromised host, blood and wound cultures are recommended. Oral or intravenous (IV) antimicrobial therapy is then started empirically, depending on the severity of the infection.[8]

The following are indications for IV antibiotics:

• A severe soft-tissue infection is limb- or life-threatening

• The signs and symptoms of systemic illness are present

• The patient is immunosuppressed

• The patient is at the extremes of age

Empirical antimicrobial therapy is administered as follows:

• Semisynthetic penicillins or second-generation cephalosporins are given to cover S aureus

• Site-specific antibiotics are given to cover indigenous organisms

• Appropriate antibiotics are given to cover methicillin-resistant S aureus (MRSA) if suspected

• Broad-spectrum antibiotics are given to patients with complicated SSTIs and immunocompromised status

After identification of the organism or organisms and confirmation of drug sensitivity, appropriate antimicrobials are started.

Less commonly used FDA-approved antibiotics for the treatment of acute bacterial skin and skin structure infections include oritavancin (Orbactiv), dalbavancin (Dalvance), and tedizolid (Sivextro),. These agents are active against S aureus (including methicillin-susceptible S aureus and MRSA] isolates), Streptococcus pyogenes, Streptococcus agalactiae, and Streptococcus anginosus group (includes Streptococcus anginosus, Streptococcus intermedius, and Streptococcus constellatus), among others. For complete drug information, including dosing, see the following monographs:

• Oritavancin

• Dalbavancin

• Tedizolid

Guidelines

The Infectious Diseases Society of America updated their guidelines for the diagnosis and management of SSTIs in 2014. For the full guidelines, see Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America.[9, 10]

The equipment required for incision, drainage, and debridement is the basic surgical set, which may include the following:

• Sponge-holding forceps

• Surgical blade, Nos. 11 and 15

• Curved artery forceps

• Plane and toothed thumb forceps

• Curette

• Metzenbaum scissors

• Sterile swab stick

• Electrocautery

• Saline

• Hydrogen peroxide

Patient preparation includes adequate anesthesia and appropriate positioning.

Anesthesia

Anesthesia for incision and drainage is as follows:

• General anesthesia: This used for large and deep abscesses to facilitate complete and thorough drainage. 
• Regional anesthesia: This can be used for large and deep abscesses if patient cooperation can be ensured.
• Field block: This is used for small to medium-sized abscesses.
• Local anesthesia: The overlying skin is anesthetized via a 26-gauge needle, and the anesthetic is infiltrated subcutaneously into the dome of the abscess to achieve anesthesia of the skin to enable painless skin incision; anesthetizing the abscess cavity is not very effective, because the local anesthetic functions poorly in the acidic environment of the abscess.

Anesthesia for debridement is as follows:

• General anesthesia: Because debridement is a very painful procedure, and complete analgesia is essential for thorough debridement.
• Regional anesthesia or field block: This may be used when general anesthesia is not desirable and patient cooperation can be ensured.

Positioning

The patient is positioned in accordance with the location of the lesion. Whichever position is chosen should afford the surgeon easy access to the lesion and should be comfortable for the patient.

Patients with complicated SSTIs or necrotizing fasciitis may have bloodstream infection (BSI) and experience septic shock. Such patients are kept under close monitoring and may require intensive care nursing. Depending on the severity of the BSI and septic shock, the patient may require intensive monitoring, along with supportive measures aimed at maintaining circulation and ventilation.

After proper positioning and anesthesia (see Periprocedural Care), incision and drainage is carried out in the following manner.

A skin incision is made with a No. 11 or 15 surgical blade in the most prominent and fluctuant part of the abscess. The direction of the incision should parallel the natural skin creases as far as possible so as to prevent unsightly scars. If there is no obvious pus pointing or fluctuant area in the abscess, the incision is made at the dependent portion of the abscess; however, a dependent incision should be avoided if a tubercular pathology is suspected.

In areas where no important neural or vascular structures are expected to be present, a bold incision that cuts through the skin, subcutaneous tissue, and deep fascia may be made to achieve entry into the abscess cavity. However, in areas where important neurovascular structures are present, only skin and subcutaneous tissue are incised. The abscess cavity is entered by insinuating a pair of blunt artery forceps or sinus forceps through a small opening in the deep fascia, then gradually opening the blades.

Once the cavity is entered, pus is seen extruding through the opening. At this point, a pus swab may be sent for microbiologic analysis if indicated. The abscess cavity is explored, and an artery forceps with a gauze piece wrapped around its tip is used to break up all the loculi and drain all the pus pockets. The same result may be achieved with the surgeon's gloved finger if the presence of a foreign body in the cavity can be ruled out.

The abscess cavity is irrigated with saline solution to flush out all the pus, debris, and blood, then packed with gauze or surgical sponge to achieve hemostasis. After a few minutes, the packing is taken out, and any active bleeding points are cauterized or ligated.

The use of wound packing is controversial but is not likely necessary. If used, packing should be inserted loosely. It is then covered with a dry absorbent dressing that soaks up exudate and blood. The dressing is changed after 24 hours and again every 24 hours thereafter until the wound is dry. When healthy granulation tissue is seen in the cavity and no fresh exudate or pus is visible, a simple dressing with gauze is sufficient.

Surgery is the most effective method of debridement. Surgical debridement is usually done with the patient under general anesthesia, but local or regional anesthesia may be employed if the lesion is not very extensive. If debridement is being done on a limb, a tourniquet may be used to minimize blood loss.

The lesion is cleaned and draped. The slough over the lesion is then slowly excised off the underlying healthy tissue with a scalpel or scissors (see the images below); smaller areas of dead tissue can be excised using a curette. The slough is excised until the wound starts bleeding, but this must be done without damaging the underlying healthy tissue. The margins of the wound are also freshened. The tourniquet is released, and any active bleeding points are cauterized.

Venous ulcer on foot.

Debridement of venous ulcer on foot.

The raw area created by debridement is covered with a nonadherent dressing (eg, tulle gras). The first dressing is changed after 24 hours; regular dressing changes follow at 24-hour intervals. At each dressing, the wound is inspected for any new slough or pus formation. Repeated debridements may be necessary until the wound becomes clean and active infection is controlled by appropriate antibiotics. Once the wound is clean, dressings may be changed at 36-hour intervals.

Other methods of debridement

Debridement methods that may be used as alternatives to surgical debridement include the following[11] :

• Mechanical

• Chemical

• Autolytic

• Biological

• Ultrasonic

Mechanical debridement is accomplished by using the wet-to-dry dressing method. The wound is dressed with a wet dressing (usually gauze soaked in saline) covered with a dry dressing. The dressing is then allowed to dry on the wound over the following 24-36 hours. When the dry dressing is taken off, it peels the adherent necrotic tissue away from the healthy tissue. This is a very painful method and is not much favored.

Chemical debridement is performed by using certain enzymatic chemicals on the wound that cause lysis of the necrotic tissue in the wound. Commercially available collagenase enzyme granules are sprinkled onto the wound daily until the wound is clear of necrotic tissue. Regular dressings then follow.

Autolytic debridement is a process in which the body sheds the dead necrotic tissue by the use of moisture. This process is helped by the presence of enzymes called matrix metalloproteinases (MMPs), which are produced by damaged tissue and which disrupt the proteins that bind the dead tissue to the body.

This process can be enhanced by applying dressings that encourage a balanced moist environment in the wound. Heavily exuding wounds benefit from the application of alginates, cellulose dressings, and foams; these dressings absorb the excess exudate and prevent maceration of surrounding healthy tissue while still maintaining a moist environment that promotes desloughing. Dry wounds benefit from the application of hydrogels and hydrocolloids, which donate moisture to the dead tissue to facilitate debridement.[12]

Biological debridement (ie, maggot therapy) involves exposing the wound to the maggots of Lucilia sericata (the greenbottle fly). These organisms digest the necrotic tissue and bacteria in the wound but spare the underlying healthy tissue. This method has not gained much favor among patients.

Ultrasonic debridement involves applying ultrasonic vibrations to the wound bed through a liquid medium. This causes cavitation (ie, the creation and destruction of small bubbles within the fluid surrounding the probe). During cavitation, the bubbles oscillate in size and shape. They expand and rapidly collapse, causing shockwave formation, and this implosion leads to erosion of tissues. Ultrasonic debridement causes necrotic tissue disruption, fragmentation and emulsion.

When a limb is being operated on, a tourniquet is used so as to obtain a bloodless field. The 3 zones of necrotizing fasciitis are delineated (see the images below). A bold incision is made that runs through the entire length of the lesion from normal skin (zone 3) proximally to normal skin distally. The incision should extend to the muscle.

Zones of necrotizing fasciitis.

Illustration of zones of necrotizing fasciitis and corresponding extent of fascial excision.

The deep fascia is identified, and a finger is passed along it to probe the extent of its involvement. Healthy deep fascia can be identified by its glistening appearance and its firm attachment to the skin and subcutaneous tissue. Unlike necrosed deep fascia, it does not separate easily from the skin and subcutaneous tissue

At this point, tissue specimens are obtained and sent for aerobic and anaerobic culture and antibiotic sensitivity and for histopathologic examination to establish the diagnosis.

Once the extent of deep fascial involvement has been established, radical excision of the deep fascia is carried out with scissors to expose the underlying healthy muscle. The overlying skin and subcutaneous tissue are then inspected for viability.

Tissues in zone 1 are necrosed and are excised. Tissues in zone 2 are inspected carefully for viability and excised when involved. Viability can be checked by looking for dermal bleeding, calcification and liquefaction of subcutaneous fat, and thrombosed blood vessels.[13] The involved skin and subcutaneous tissue is excised.

The tourniquet is then deflated, and the tissue is examined for viability. Further debridement is carried out if necessary. Once debridement is complete, hemostasis is achieved by means of electrocauterization, and the wound is washed thoroughly with saline.

The extensive debridement required in cases of necrotizing fasciitis results in a large raw wound. The wound is carefully dressed with a nonadherent dressing and bandaged with absorbent dressing. The dressing is changed after 24 hours.

Bleeding is the most common complication associated with these procedures. Bleeding after debridement (especially debridement for necrotizing fasciitis) may cause rapid deterioration of an already compromised patient. Meticulous hemostasis is hence mandatory. In most cases, pressure dressing is sufficient to control the bleeding; in some cases, the patient may have to be returned to the operating room for control of persistent bleeding.

Drainage of an abscess or debridement of necrotic tissue may result in dissemination of bacteria and bacterial toxins into the bloodstream and thereby cause severe sepsis. Accordingly, it is imperative that these procedures be done under antibiotic coverage.

Injury to underlying nerves and blood vessels is another potential complication. The surgeon must be careful while making the incision and during debridement if the abscess or ulcer is in close proximity to important anatomic structures such as nerves and blood vessels.