Chapter 8: Inflammation, Infection, & Antimicrobial Therapy in Surgery

INTRODUCTION

TERMINOLOGY

Surgery and infection are unfortunately intimately intertwined. For the purpose of this chapter, we will differentiate between infections resulting from surgery (surgical site infections) and those resulting from other disease processes but requiring surgical management. Surgical incisions involve a breach of the skin and immune barriers, and can thus be complicated by infection. The term “wound infection” has been replaced by the more accurate term “surgical site infection” (SSI), to emphasize that the infection can occur anywhere within any of the areas accessed surgically (not exclusively at the skin level) and to differentiate it from “traumatic wound infection.”

As opposed to SSI, the term “surgical infection” is used to indicate infections that are unlikely to respond to medical and antimicrobial treatments, and require surgical intervention or management. Common examples include abscesses, empyema, intra-abdominal infections, and necrotizing skin and soft tissue infections. Surgical decision making involves, at its core, the knowledge and experience to determine the timing of surgery and a right balance between surgery and other adjunct therapy such as antibiotic therapy, resuscitative efforts, and nutritional optimization, in order to provide the patient with the best chances to cure the infection with the best overall outcomes.

Pathogenesis

The development of a surgical infection involves a close interplay between three elements:

1. A susceptible host

2. An infectious agent

3. A suitable medium or environment (Figure 8–1).

The degree of contribution of each of these three factors to the eventual occurrence of the infection depends on the individual patient and the specific nature and site of the infection. Whether a given inoculum of bacteria results in an established infection or not depends on the virulence of the bacteria, the strength of the immune and inflammatory host response (eg, chemotaxis, phagocytosis, B- and T-lymphocyte activation), and the amount of blood perfusion and oxygen tension in the medium where the inoculum resides.

A. The Susceptible Host

Many surgical infections occur in patients with no evidence of decreased immune defenses. However, with the major advances in medicine and health care services over the last century, more immunocompromised patients (eg, transplant, HIV, and diabetic patients) are presenting with infections requiring surgical management or with SSIs following surgical interventions. Table 8–1 delineates a list of patient-related conditions associated with decreased immunity and potential predisposition to surgical infections. The mechanisms by which the listed conditions affect a host’s immunity are diverse in nature. For example, diabetic patients have suboptimal neutrophil adherence, migration and anti-bacterial functions, making them less able to fight an occult infection. Such effect of diabetes on immunity is much more pronounced in patients ...