How To Address Post-Op Infections In Patients With Diabetes
Given the elevated risk of surgical site infections in patients with diabetes, increased vigilance is crucial. This author discusses risk factors that can lead to post-op infections, keys to diagnosis and pertinent pearls on effective treatment.
The successful treatment of surgical site infections (SSIs) in patients with diabetes mellitus can prove challenging to clinicians. The SSI rate following elective, clean foot and ankle surgery in the non-diabetic patient is relatively low at less than 2.1 percent, according to the Centers for Disease Control and Prevention (CDC).1 Recent study data suggests, however, that patients living with diabetes have about a fivefold increased risk for developing a severe infection postoperatively in comparison to patients without diabetes.2
This is significant. Clinicians who are involved in the surgical care of patients with diabetes must adequately understand the risks and distinctive challenges posed by this patient population.
Lower extremity infection in the patient with diabetes is a major risk factor for non-traumatic limb loss. Nearly 83 percent of all non-traumatic lower extremity amputations (LEA) in the United States are secondary to complications associated with diabetes mellitus. It has been well documented in the literature that the consequences of major LEA in patients with diabetes are severe with an estimated five-year postoperative survival rate of less than 50 percent.3 This suggests that mortality associated with diabetic LEAs exceeds that of most cancers.
Furthermore, studies have demonstrated that nearly 77 percent of the deaths of surgical patients were related to the development of SSI.3 It is vital, therefore, that clinicians involved in surgery be appropriately qualified to manage these complications to reduce potential patient morbidity and mortality.
Prior to detailed discussion regarding SSI, it is important that the clinician have a full understanding regarding the terminology utilized to describe these postoperative complications. Surgical site infections have a wide spectrum of possible clinical features and there have consequently been several attempts to classify these infections based upon salient clinical features.
Perhaps the most appropriate definitions have been proposed by the CDC following attempts to standardize data collection for the National Nosocomial Infection Surveillance (NNIS) program.1 This program classifies infection into incisional infections, which can be superficial or deep, or organ/space infections, which affect the rest of the body other than the body wall layers.
Superficial incisional infections involve skin and subcutaneous layers while deep incisional infections involve deeper structures, such as fascial and muscle layers. Organ/space infections can be either superficial or deep, and involve any anatomy, other than the incision site, which the surgeon manipulated during the surgical procedure. An example of this in lower extremity surgery would be pin site placement in the use of external fixation. Superficial incisional infections account for more than half of all SSI for all categories of surgery.1
What Are The Risk Factors For Infection?
The frequency of SSI is clearly related to the category of operation one is performing. The NNIS defines clean and low-risk operations as having the lowest rate of infection, and contaminated and high-risk operations having greater infection rates.1 In addition to the category of surgery, there are numerous factors that combine to increase the risk of postoperative infections. These factors include:
1) patient-related factors (such as concomitant comorbidity including diabetes mellitus);
2) procedure-related factors (such as placement of internal fixation or prosthetics, and severity of trauma to the patient);
3) microbial factors that contribute to the aggressiveness or invasiveness of the bacteria; and
4) the use of perioperative antibiotics when indicated.
A recent study in the Journal of Bone and Joint Surgery demonstrated that, among patient-related factors, peripheral neuropathy was the greatest risk factor for the development of SSI in patients with and without diabetes.2 In addition, Wukich and colleagues noted that Charcot neuroarthropathy, diabetes mellitus, peripheral arterial disease (PAD), the use of external fixation, longer duration of surgery and older patient age each increased the risk for the development of SSI postoperatively.
The study by Wukich and colleagues consists of a retrospective analysis of 1,000 patients and an overall infection rate of 4.8 percent.2 The authors excluded patients with obvious preoperative infection. They defined postoperative infection as infection that occurred within 30 days of surgery in patients without external fixation, and infection that occurred up to 30 days after removal of the frame in patients who had been placed in external fixation.
The control group (patients without diabetes) demonstrated an infection rate of 2.8 percent.2 The study group demonstrated an infection rate of greater than 13 percent. Interestingly, authors found no significant association between developing a postoperative infection and tobacco use, gender, previous surgical transplantation or whether patients had inpatient or outpatient surgery.
In addition to patient-related factors, one must not ignore procedure-related factors that contribute to the risk of developing SSI. Among these, selection of fixation techniques, such as external fixation, can significantly increase the risk of infection.4 Interestingly, in their study, Wukich and co-workers found that use of external fixation was associated with 40 percent of infections in the study.2 When they occurred, these infections were remote from the incision and were associated with pin sites.
Apart from fixation techniques, other procedure-related factors can contribute to the risk of developing infections. These include potential improper use of perioperative antibiotics, inadequate operating room ventilation and a crowded operating room during surgery.
Keys To Ensuring An Accurate Diagnosis
Successful treatment of lower extremity SSI requires appropriate and timely diagnosis to limit the propagation of the pathological process. When it comes to diagnosing post-op infections, the physical appearance of the incision probably provides the most reliable information. The clinical diagnosis should be based upon the presence of gross purulent secretions or at least two cardinal manifestations of inflammation.5-7 These include redness, warmth, swelling and pain or tenderness.
It is necessary to determine the clinical extent of the infection, the microbial etiology of infection and any other contributing patient-related factors, such as the presence of peripheral vascular disease, that one needs to address in conjunction with SSI management. Central to the diagnosis of infection is obtaining appropriate culture data to help guide subsequent treatment decisions. Appropriate laboratory data, such as complete blood counts (CBC), basic metabolic profile (BMP) and blood cultures, may be necessary if patients present with systemic signs and symptoms.8
Essential Microbiological Insights
When considering SSIs, the predominant microorganisms involved are aerobic, gram-positive cocci. The Infectious Diseases Society of America (IDSA) demonstrated that Staphylococcus aureus and the ß-hemolytic streptococci (groups A, C and G, but especially group B) are the most commonly isolated pathogens in SSI.8,9
Unfortunately, SSIs secondary to antibiotic-resistance organisms are becoming increasingly common. These include methicillin resistant Staph aureus (MRSA) and vancomycin-resistant Enterococci (VRE). Although MRSA strains have previously been isolated mainly from hospitalized patients, community-associated cases are now becoming common.10-12 When isolated, antibiotic-resistant strains are associated with worse outcomes in patients with diabetic foot infections.9,13
Acute SSIs, especially in patients who have not received recent antimicrobial treatment, are commonly monomicrobial.2 In contrast, those patients who present with chronic infection are more likely to present with polymicrobial infections in which culture data may yield three to five isolates, including both gram-positive and gram-negative anaerobes.14 However, in those cases in which one obtains multiple isolates, the pathogenic role of each isolate is unclear and many may indeed represent colonization alone.
A Guide To Managing Surgical Site Infections
The management of SSI in patients with diabetes involves determining the severity of the infection as well as any contributing factors that one needs to address. It is common for diabetic foot infections to require both local and systemic management. Accordingly, these complex patients require a coordinated effort for effective treatment.
It is my recommendation that an interdisciplinary team coordinate these efforts. There is an abundance of literature to support the use of interdisciplinary teams to improve limb preservation and salvage outcomes in complex patients with diabetes.15 The core of this interdisciplinary team model involves the ability to rapidly diagnose and provide treatment to patients with lower extremity complications of diabetes. Such patients should have ready access to an infectious diseases specialist or a medical microbiologist to provide appropriate direction for antibiotic coverage.15,16
Upon first presentation and clinical suspicion of SSI, one should initiate empiric antibiotic therapy. After deciding to start treatment for infection, selection of the antibiotic regimen initially involves decisions about the route of therapy, the spectrum of microorganisms to be covered and the specific drugs to administer. Later, one will choose the definitive regimen and the duration of treatment.9,15 It is important to adequately triage those patients with moderate and severe infections who require hospitalization and empirical parenteral antibiotics, differentiating such patients from those one can treat appropriately with oral antibiotic therapy.17
Several treatment algorithms have been proposed to address the management of lower extremity infection in those with diabetes. In some cases, it can be difficult to ascertain the severity of postoperative infection in patients with diabetes due to a compromised immune response. Indeed, one study demonstrated that 50 percent of patients with a limb-threatening infection do not manifest systemic signs or symptoms.9
When it comes to mild and some moderate infections, physicians may employ oral antibiotics with fairly specific activity against aerobic gram-positive organisms. Regardless of the severity of infection, one should place all patients on initial empiric, broad antibiotic converge until more focused therapy can begin on the basis of appropriate culture results.
When considering possible drug resistant microbes, be advised that many community-acquired MRSA strains remain susceptible to trimethoprim-sulfamethoxazole and tetracycline although treatment failure rates of 21 percent have been reported in some series with doxycycline or minocycline.18,19 When sending patients home with these regimens, it is recommended to re-evaluate them at 24 to 48 hours to verify a clinical response.18 Progression of infection, despite antibiotic usage, could be due to infection with resistant microbes or the presence of a deeper, more serious infection than one previously realized.
When it comes to the management of SSIs, hospitalization is occasionally required. Patients with severe SSI or those who present with significant patient-related factors, such as significant medical comorbidities, commonly require hospitalization. Even in the absence of significant infection, those patients who present with mild to moderate infections may benefit from hospital admission if there are significant complicating factors that may affect their wound care or adherence to antibiotic treatment.7
In some instances, surgical intervention may even be indicated. This surgical intervention may range from incision and drainage of infected and necrotic tissue to limb revascularization and complex soft tissue reconstruction.9,10,14 Several authors advocate that for those patients with significant infections, the primary and most important therapy is to open the incision, evacuate the infected material and continue dressing changes until the wound heals by secondary intention.20
Post-op infections are the most common adverse events affecting hospitalized patients who have undergone surgery and these can be of particular concern in patients with diabetes. Studies have demonstrated that patients living with diabetes are at five times greater risk for the development of severe SSI in comparison to non-diabetic patients.2 This increased risk is likely due to a variety of patient-related factors, including the prevalence of comorbidity common in patients with diabetes.
Certainly, in the context of SSI management, it is necessary that clinicians address any contributing health factors that may preclude normal healing in the patient with diabetes. Early and appropriate diagnosis with timely medical and surgical intervention is vital in the management of infections. It is important that the clinician involved in the management of these challenging patients recognize that patients with diabetes may demonstrate muted signs and symptoms in the context of infection secondary to attenuated immune responses.
Clinicians should maintain appropriate clinical suspicion in postoperative patients with diabetes who present with surgical wounds that appear other than expected. Maintaining such vigilance will allow for early intervention and effective management to reduce potential morbidity and mortality associated with lower extremity infection in the diabetic patient population.
Dr. Fitzgerald is in private practice at Hess Orthopaedics and Sports Medicine in Harrisonburg, Va. He is an Associate of the American College of Foot and Ankle Surgeons.
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2. Wukich DK, Lowery NJ, McMillen RL, et al. Postoperative infection rates in foot and ankle surgery: a comparison of patients with and without diabetes mellitus. J Bone Joint Surg Am. 2010; 92(2):287-95.
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16. Fitzgerald RH, Bharara M, Mills J, et al. Use of a Nanoflex powder dressing for wound management following debridement for necrotising fasciitis in the diabetic foot. Int Wound J. 2009; 6(2):133-9.
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20. Stevens DL. Antimicrobial agents for complicated skin and skin-structure infections: noninferiority margins, placebo-controlled trials, and the complexity of clinical trials. Clin Infect Dis. 2009; 49(3):392-4.