Pathogenesis and Clinical Features

One of the most common and likely underreported complications following operative procedures is the development of a wound seroma ( Fig. 9.1A ). Although typically a benign finding, when not treated, seromas may lead to more serious wound infections, wound breakdown, or potentially skin necrosis. A seroma is a collection of sterile, clear, ultrafiltrated serum, lymphatic fluid, or liquified fat. The fluid is usually clear, amber, and slightly viscous. Seromas are located under the incision, above the fascial layer, and directly beneath the dermis of the skin. They are more likely to occur when large tissue flaps are mobilized or when extensive lymphadenectomy is performed, such as during axillary or inguinal lymph node dissection. Thus, efforts to limit the extent of dissection where feasible without compromising cancer control such as sentinel lymph node procedures or preservation of the saphenous vein during inguinal lymphadenectomy may reduce the risk of seroma formation.

Selected wound complications. A, Seroma (arrow) as seen on postoperative cross-sectional imaging. (Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.) B, Superficial surgical site infection (SSI) healing by secondary intention. (Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.) C, Superficial SSI managed with vacuum-assisted closure with surrounding cellulitis. (Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.) D, Fascial wound dehiscence.

(Used with permission of Mayo Foundation for Medical Education and Research, all rights reserved.)

Prevention and Management

Most postoperative seromas are discovered incidentally and require no active intervention. However, when large or symptomatic, seromas can be evacuated by opening the overlying skin edges, packing the wound with sterile saline-soaked gauze, and allowing the wound to heal by secondary intention. Seromas that develop under flaps (i.e., after inguinal lymph node dissection), however, may be more difficult to manage because these have the potential to damage the delicate vascular supply to the flap. Therefore, in incisions that involve extensive skin flaps, placement of closed-suction drains is typically performed and recommended. These drains are left in place until their output decreases to a minimal amount (typically <30 mL in a 24-hour period). Pressure dressings may be useful postoperatively when seroma formation is of concern. Occasionally, premature removal of the drains may allow a seroma to develop, and percutaneous aspiration or drain placement may be required.

Pathogenesis and Clinical Features

A hematoma is a collection of blood in or near a recent surgical incision. Hematomas typically occur in the subcutaneous space, but they may also occur deeper in the incision, such as in the rectus sheath. Wound hematomas are most often caused by inadequate hemostasis after the skin has been closed. Many factors contribute to the formation of hematomas. First, hemostasis at the time of wound closure may be inadequate. Extra care should be taken in patients who are hypotensive or in shock at the time of wound closure. Additionally, the use of epinephrine may mask small bleeding vessels during closure. Postoperatively, anticoagulants such as aspirin, nonsteroidal antiinflammatory drugs, heparin, and warfarin also increase the likelihood of postoperative bleeding and therefore should be used with care in the perioperative period. Finally, a host of disease processes may be present that may predispose patients to the development of hematomas, including myeloproliferative disorders, renal or hepatic insufficiency, deficiency of clotting factors, and platelet dysfunction.

Hematomas usually manifest by ecchymosis of the overlying skin, localized wound swelling, pain or pressure, and drainage of blood from the surgical site. The diagnosis can be confirmed by inspection, palpation, and gentle probing of the wound. If these measures prove insufficient, ultrasound evaluation can be useful to delineate the hematoma. In addition, large rectus sheath hematomas may manifest with signs of significant hemorrhage, including hemodynamic shock. Often these hematomas result in large ecchymoses that track subcutaneously a long distance from the patient’s surgical site. Large hematomas that collect in the retroperitoneum or rectus sheath may cause paralytic ileus, anemia, and ongoing bleeding resulting from the consumption of coagulation factors. One of the most common problems associated with the development of a surgical hematoma is the risk of secondary infection. Blood is a good medium for growth of bacteria that may infiltrate the hematoma and result in a substantial surgical site infection (SSI).

Prevention and Management

The most important factor in the prevention of wound hematoma is meticulous hemostasis at the time of closure of the subcutaneous tissue. Prevention is also facilitated by correction of all clotting abnormalities preoperatively and by discontinuing all medications that can prolong the bleeding time. In addition, wounds that involve large skin flaps or those with large potential spaces in which blood could collect should be drained with a closed-suction surgical drain until the output of these drains decreases. Management of wound hematomas is similar to management of wound seromas, discussed earlier.

Definition

The term surgical site infection distinguishes a postoperative infection from a traumatic wound infection. The Centers for Disease Control and Prevention (CDC) developed a universal nomenclature for SSIs that involves categorization according to the depth of infection ( Fig. 9.2 ). Infections that are confined to the skin and subcutaneous tissue (above the fascia) are considered superficial incisional SSIs . These infections account for the majority of all SSIs. Infections that involve the deep soft tissue (below the fascia) are termed deep incisional SSIs . Deep incisional SSIs include postoperative necrotizing fasciitis and osteomyelitis. Finally, an infection that involves an organ space that was manipulated during a procedure is termed an organ space SSI . Organ space SSIs may include peritonitis or other infections that involve the cavitary space entered during the procedure. Usually these infections are diagnosed within 30 days of the procedure. An exception to this rule is the case of implanted material, when SSIs are recorded up to 1 year from the surgical procedure and appear to be related to the operation.

Centers for Disease Control and Prevention classification of surgical site infection (SSI). Superficial incisional SSIs are limited to skin and subcutaneous tissues and deep incisional SSIs involve muscle and fascia, whereas organ space SSIs include infections within the cavitary space of the procedure.

(Copyright © 2007, Mayo.)

Risk Stratification

The development of an SSI depends on complex interactions between the pathogenic organism and the host’s local and systemic defense mechanisms. Factors influencing the pathogenic organism include the virulence of the contaminating organism itself and the number of organisms inoculated into the wound. In 1964, the National Research Council (NRC) of the National Academy of Sciences reported on a study designed to evaluate the effect of ultraviolet irradiation on postoperative infections. Although this study did not reach its desired end point, it was the first effort to categorize incisions based on the estimated degree of bacterial contamination. The four categories of incision described by the NRC ( Table 9.1 ) remain the most widely accepted classification of surgical wounds to date, and the system remains useful to estimate the risk of SSI, predict pathogens, and determine the need for antimicrobial prophylaxis. This effort represented the first connection between the contaminating flora at various surgical sites and the subsequent infecting pathogens:

• 
  

  Class I, or clean, wounds: Those wounds in which only skin flora are likely to contaminate the operative field because no hollow viscus has been entered. The risk of infection in these cases is low (0.5–2%). A subset of class I wounds, class I _D , consists of wounds in which prosthetic material is implanted. These wounds are classified differently because, although the incidence of infection is also low, the consequences of the infection can be dire and may obviate the entire purpose of the procedure.

  
  
• 
  

  Class II, or clean-contaminated, wounds: Those wounds in which a hollow viscus likely to harbor bacteria is entered under controlled circumstances. In these cases, both skin flora and microbes within the viscus may contribute to the SSI and thus the incidence of infection is higher (2–5%).

  
  
• 
  

  Class III, or contaminated, wounds: Those wounds in which substantial microbial contamination exists and the risk of infection is even greater (5–15%), particularly if the skin is closed.

  
  
• 
  

  Class IV, or dirty-infected, wounds: Those wounds in which the wound is infected preoperatively and the organisms causing the postoperative infection are presumed to be present before the surgical procedure.

In an effort to improve this risk stratification for SSIs the CDC introduced the National Nosocomial Infection Surveillance (NNIS) risk index. The NNIS risk index incorporates additional patient- and procedure-related factors into the previously described wound classification. It is operation specific and assigns points based on patient-related risk factors (as defined by the American Society of Anesthesiologists preoperative assessment score), the duration of the operation, and the degree of microbial contamination of the incision. The duration of the operation is important because lengthy procedures may result in increased exposure to microbial contamination as well as compromised local defenses resulting from desiccation, hypothermia, and lower concentrations of prophylactic antibiotics.

Since the NNIS risk index was produced, additional risk factors for SSIs have been identified. For example, hypothermia has been identified as an independent risk factor for infection, and therefore maintenance of normothermia is an important aspect of intraoperative and postoperative care. Strict glucose control has been independently associated with decreased wound infection rates as well as with decreased mortality in an intensive care setting. Serum albumin level has long been identified as an important risk factor because it reflects a wide range of comorbid conditions that contribute to wound healing. Other important risk factors are age, vascular insufficiency, diabetes, radiation, preoperative smoking, and obesity.

Microbiology

Endogenous pathogenic organisms implicated in SSI most commonly come from the patient’s skin, alimentary tract, or genitourinary tract. The patient’s microflora may be altered by preoperative admission to the hospital. In fact, a demonstrable shift in the microbial environment toward more resistant bacterial species occurs within 48 to 72 hours of hospital admission. Exogenous contamination can be minimized by strictly following aseptic technique and maintaining a sterile operating room environment.

The most common organisms isolated from surgical sites remain gram-positive cocci, specifically Staphylococcus aureus ( Table 9.2 ). However, gram-negative infections are common in class II wounds. It is important to recognize the type of infection associated with various operative sites to select appropriate antimicrobial prophylaxis.

Prevention

Diagnosis and Management

Most SSIs manifest within 4 to 8 days of the surgical procedure. However, they may manifest within 30 days of the operation or up to 1 year in cases with implanted prosthetic material. This finding implies that, in the current medical environment of outpatient surgery or early discharge, most of these infections occur in the outpatient setting. This implication emphasizes the importance of patient education in the postoperative period. Patients should be aware of the signs and symptoms of SSI and should know when to seek additional care.

The diagnosis of SSI is clinical and has been described for as long as surgical procedures have been performed. Classically, the most common symptoms have been described (in Latin) as rubor (“erythema”), dolor (“pain”), tumor (“induration”), and calor (“warmth”). Some patients may also note drainage from the wound or separation of the skin closure. If the SSI is not treated, systemic symptoms may develop, including fever (38–39°C), fatigue, leukocytosis, and increased heart rate.

The management of SSI depends on the extent and type of infection. Drainage and debridement have been and remain the cornerstones of management. Superficial SSIs are treated by opening the incision to provide adequate drainage. A small piece of saline-soaked gauze may be placed in the wound to serve as a wick and to prevent closure of the skin while allowing deeper aspects of the wound to heal by secondary intention. Wet-to-dry dressing changes have been a staple of wound care after SSI, although it may take several weeks to months for the wound to heal by secondary intention (see Fig. 9.1B ). A culture and Gram stain may identify the offending organism, although these methods are not always necessary. In the setting of superficial SSI, antibiotics need be given only when patients are at risk for systemic dissemination of the infection. Severe infections, such as necrotizing fasciitis, represent surgical emergencies, and patients should be taken immediately back to the operating room for wide debridement. The identification of only “dishwater” pus, subcutaneous crepitus, or sepsis should alert the clinician to the possibility of necrotizing fasciitis. These infections progress rapidly and are caused by either Clostridium perfringens or group A β-hemolytic streptococci.

The development of vacuum-assisted closure has eased the process of multiple daily dressing changes (see Fig. 9.1C ). Vacuum-assisted closure was designed to promote healing of large wounds by constant or oscillating application of negative pressure. This negative pressure promises to increase local blood flow, control exudates, and reduce edema of the surrounding tissue. In our experience, these negative pressure techniques have proved useful in treating large, chronic wounds. However, their use should be limited when wounds are near conduits, anastomoses, and neobladders because in our experience, they may be associated with an increased rate of cutaneous fistula formation.

Pathogenesis and Clinical Features

Surgical wound dehiscence (see Fig. 9.1D ) is one of the most alarming complications faced by abdominal surgeons. Put simply, a dehiscence represents the mechanical failure of wound healing and is defined as a separation of the facial layers early in the postoperative period. Evisceration, in turn, is a related term referring to the extrusion of peritoneal contents through the dehisced wound. Dehiscence is of great concern because it may rapidly lead to evisceration. Abdominal dehiscence with evisceration has been associated with a mortality rate nearing 50%. When diagnosed early in the postoperative period, complete wound dehiscence almost always requires a return to the operating room for fascial closure or repair. However, small partial wound dehiscences that are diagnosed >2 weeks postoperatively may often be watched with delayed repair of the resultant incisional hernia, because the risk of evisceration is very low in such patients.

Unfortunately, wound dehiscence frequently occurs without warning. Up to 80% of the time, it manifests as sudden, dramatic drainage of a large volume of clear, serous fluid from the incision. Patients may also note a pulling or ripping sensation. This often occurs when the patient is standing or changing positions, because the pressure on the incision is greatest at these times. The diagnosis is then confirmed by gently probing the incision with a sterile, cotton-tipped applicator to determine the integrity of the fascia. If clinical suspicion remains despite equivocal physical examination findings, imaging studies such as ultrasound or computed tomography can be used. When a large segment of the incision is open, immediate plans for closure in the operating room should be made. In the event of evisceration, the eviscerated intraperitoneal contents should be covered with a sterile saline moistened towel until an emergency operation can be performed.

Numerous factors can contribute to wound dehiscence ( Table 9.3 ). However, despite advances in suture material and perioperative care, the incidence of abdominal fascial dehiscence has remained steady at nearly 1% of abdominal wounds. Other factors that contribute to wound dehiscence remain. Obesity, for example, is associated with increased difficulty in identifying the fascia and in closing the incision. Corticosteroids, over long periods, can decrease the tensile strength of healing wounds. Patients with cancer are more likely to have problems with wound healing, because these patients are more likely to have a contaminated wound and have undergone previous irradiation or chemotherapy. Radiation causes obliterative sclerosing endarteritis that can decrease the microvascular arterial supply to the wound. Malnourished patients nearly uniformly have decreased protein synthesis and turnover, which lead to poorer fascial integrity. Finally, diabetic patients encounter more healing problems than do patients without diabetes and have a greater risk of wound dehiscence. The likely reason is that diabetic patients have less collagen synthesis and deposition, decreased wound breaking strength, and impaired leukocyte function.

Suture Selection and Technique

Wounds have <5% of normal tissue strength during the first postoperative week and may not ever develop normal tensile strength. In fact, studies have demonstrated that abdominal fascia regains 50% to 59% of this original tensile strength at 7 weeks and 70% to 90% at 20 weeks but may never exceed 93% of uninterrupted fascia. Therefore initial postoperative wound security depends solely on suture strength and technique of closure. As such, the choice of suture material is of critical importance in closing abdominal surgical wounds. The suture material should be strong enough to reapproximate the tissue and keep the wound intact during normal postoperative activity.

Numerous suture materials are available for wound closure. These sutures can be classified as natural or synthetic as well as rapidly absorbable, slowly absorbable, and nonabsorbable. Synthetic material has the advantages of being more uniform, inducing less tissue reaction, having greater tensile strength for a given diameter, and eliminating the risk of disease transmission. In 2001 the United Kingdom eliminated the use of catgut suture because of the risk of transmission of bovine spongiform encephalopathy (BSE, or mad cow disease).

Nonabsorbable sutures have been widely used to close abdominal incisions for many years. However, stainless steel wire and braided silk, once commonplace, have been replaced by more modern suture materials. Nonabsorbable monofilament sutures are associated with less tissue reaction and more resistance to infection than are absorbable sutures. However, they are associated with a higher incidence of sinus formation and long-term wound pain. The primary benefit of nonabsorbable sutures is that they maintain tensile strength throughout the process of wound healing.

Absorbable sutures are designed to reapproximate the fascia through the initial phases of wound healing until the fascia itself has regained enough tensile strength. Rapidly absorbable sutures are not recommended for closure of abdominal incisions because this suture type has been demonstrated to have a higher incidence of wound dehiscence and postoperative hernia formation when compared with nonabsorbable sutures. However, slowly absorbable sutures, such as polydioxanone (PDS) and polyglyconate (Maxon), have been shown to cause less incisional pain and suture sinuses, with no effect on the long-term hernia rate. Additionally, these newer-generation monofilament sutures are more resistant to infection than are multifilament sutures. They are degraded by hydrolysis and are not as subject to enhanced absorption resulting from bacterial enzymatic activity.

When a suture is placed through the fascia in the operating room, wound dehiscence has three potential causes:

• 
  
  
  
  
  
  • 1.
    

    The suture may break

    
    
  • 2.
    

    The knot may slip

    
    
  • 3.
    

    The suture may cut through the tissue.

  
  

Several studies have demonstrated that suture breakage and knot failure are rarely the source of wound dehiscences, and in the majority of wounds that have dehisced, the suture and knots are intact but the suture has torn through the fascia. This finding brings to light the importance of suture diameter because smaller-diameter sutures are associated with a greater likelihood of tearing through tissue. Therefore most sutures used for abdominal wound closure are number 0 or larger. Additionally, the use of continuous running looped sutures has gained popularity as a method to increase the speed and tensile strength of wound closure. A double-looped closure has been demonstrated to be the strongest method of wound closure, but it has been associated with increased pulmonary complications, potentially because of decreased abdominal compliance.

Surgical dictum states that sutures should be placed ≥1 cm from the fascial edge while advancing ≤1 cm with each throw. This recommendation results from concern for thermal injury related to the use of electrocautery on the fascial edge. Jenkins demonstrated that the length of a midline laparotomy can increase up to 30% in the postoperative period as a result of elasticity and increased intra-abdominal pressure. Therefore it is important when closing using a running suture that the suture is of adequate length. Investigators have demonstrated that wounds that have been closed with a suture length that is twice as long as the wound have a higher rate of wound dehiscence than do wounds closed with suture that is four times the length of the wound. This concept is referred to as the suture-to-wound length ratio, and a ratio of at least 4 : 1 provides good wound security. Theoretically, this approach affords adequate approximation of the fascial tissues while minimizing the ischemic effects of increased tension along the suture line.

Layered Versus Mass Closure

Layered closure of the abdominal wound involves separate closure of each of the distinct fascial layers with or without closure of the peritoneum. Mass closure, or Smead-Jones closure, is the closure of all layers of the abdominal wall, except the skin, as a single structure. Classically, this approach involved interrupted sutures. However, no benefit has been demonstrated over a continuous suture technique. Layered closure was believed to decrease intraperitoneal adhesions, increase wound strength, and promote hemostasis. These effects were especially noted with paramedian incisions, which currently are used less frequently than are muscle-splitting midline incisions. However, several prospective, randomized studies and large meta-analyses demonstrated that layered closure is associated with higher rates of dehiscence and prolonged operative times as compared with mass closure. Separate peritoneal closure, in particular, has been associated with more intraperitoneal adhesions, increased operative times, and obscured fascial closure. Furthermore, evidence indicates that the peritoneum re-epithelializes within 48 to 72 hours without closure, and separate closure of this layer is unnecessary.

Retention sutures are sutures that are placed through all layers of the abdomen, including skin. They are often secured around a piece of rubber tubing and tied down ( Fig. 9.3 ). Although historically they were used to decrease the incidence of abdominal dehiscence in patients at high risk, more recent studies did not demonstrate a beneficial effect on the rate of dehiscence. These sutures have also been associated with increased pain and inconvenience.

Retention sutures are placed through all layers of the abdominal wall and are secured around rubber tubing.

(Copyright © 2007, Mayo.)

Pathogenesis and Clinical Features

Surgical wound dehiscence (see Fig. 9.1D ) is one of the most alarming complications faced by abdominal surgeons. Put simply, a dehiscence represents the mechanical failure of wound healing and is defined as a separation of the facial layers early in the postoperative period. Evisceration, in turn, is a related term referring to the extrusion of peritoneal contents through the dehisced wound. Dehiscence is of great concern because it may rapidly lead to evisceration. Abdominal dehiscence with evisceration has been associated with a mortality rate nearing 50%. When diagnosed early in the postoperative period, complete wound dehiscence almost always requires a return to the operating room for fascial closure or repair. However, small partial wound dehiscences that are diagnosed >2 weeks postoperatively may often be watched with delayed repair of the resultant incisional hernia, because the risk of evisceration is very low in such patients.

Unfortunately, wound dehiscence frequently occurs without warning. Up to 80% of the time, it manifests as sudden, dramatic drainage of a large volume of clear, serous fluid from the incision. Patients may also note a pulling or ripping sensation. This often occurs when the patient is standing or changing positions, because the pressure on the incision is greatest at these times. The diagnosis is then confirmed by gently probing the incision with a sterile, cotton-tipped applicator to determine the integrity of the fascia. If clinical suspicion remains despite equivocal physical examination findings, imaging studies such as ultrasound or computed tomography can be used. When a large segment of the incision is open, immediate plans for closure in the operating room should be made. In the event of evisceration, the eviscerated intraperitoneal contents should be covered with a sterile saline moistened towel until an emergency operation can be performed.

Numerous factors can contribute to wound dehiscence ( Table 9.3 ). However, despite advances in suture material and perioperative care, the incidence of abdominal fascial dehiscence has remained steady at nearly 1% of abdominal wounds. Other factors that contribute to wound dehiscence remain. Obesity, for example, is associated with increased difficulty in identifying the fascia and in closing the incision. Corticosteroids, over long periods, can decrease the tensile strength of healing wounds. Patients with cancer are more likely to have problems with wound healing, because these patients are more likely to have a contaminated wound and have undergone previous irradiation or chemotherapy. Radiation causes obliterative sclerosing endarteritis that can decrease the microvascular arterial supply to the wound. Malnourished patients nearly uniformly have decreased protein synthesis and turnover, which lead to poorer fascial integrity. Finally, diabetic patients encounter more healing problems than do patients without diabetes and have a greater risk of wound dehiscence. The likely reason is that diabetic patients have less collagen synthesis and deposition, decreased wound breaking strength, and impaired leukocyte function.

Table 9.3

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