Schwartz's Principles of Surgery ABSITE and Board Review, 9th Ed.

CHAPTER 6. Surgical Infections

BASIC SCIENCE QUESTIONS

1. Which of the following is a critical component of the initial response to bacterial contamination of the peritoneal cavity?

A. Macrophage upregulation

B. Platelet adherence

C. Phagocytosis by PMNs

D. Opsonization

Answer: A

Microbes also immediately encounter a series of host defense mechanisms that reside within the vast majority of tissues of the body. These include resident macrophages and low levels of complement (C) proteins and immunoglobulins (Ig, antibodies). Resident macrophages secrete a wide array of substances in response to the above-mentioned processes, some of which appear to regulate the cellular components of the host defense response. Macrophage cytokine synthesis is up-regulated. Secretion of tumor necrosis factor alpha (TNF-α), of interleukins (IL)-1β, 6, and 8; and of interferongamma (INF-γ) occurs within the tissue milieu, and, depending on the magnitude of the host defense response, the systemic circulation. Concurrently, a counterregulatory response is initiated consisting of binding proteins (TNF-BP), cytokine receptor antagonists (IL-1ra), and anti-inflammatory cytokines (IL-4 and IL-10). The interaction of microbes with these first-line host defenses leads to microbial opsonization (C1q, C3bi, and IgFc), phagocytosis, and both extracellular (C5b6-9 membrane attack complex) and intracellular microbial destruction (phagocytic vacuoles). Concurrently, the classic and alternate complement pathways are activated both via direct contact with and via IgM > IgG binding to microbes, leading to the release of a number of different complement protein fragments (C3a, C4a, C5a) that are biologically active, acting to markedly enhance vascular permeability. Bacterial cell wall components and a variety of enzymes that are expelled from leukocyte phagocytic vacuoles during microbial phagocytosis and killing act in this capacity as well. (See Schwartz 9th ed., p. 116.)

2. Severe sepsis is differentiated from sepsis by

A. A history of premorbid conditions such as diabetes

B. Positive blood cultures for bacteria or fungus

C. Acute organ failure such as renal insufficiency

D. Prolonged arterial hypotension

Answer: C

SIRS caused by infection is termed sepsis and is mediated by the production of a cascade of proinflammatory mediators produced in response to exposure to microbial products. Severe sepsis is characterized as sepsis (defined above) combined with the presence of new-onset organ failure. Severe sepsis is the most common cause of death in noncoronary critical care units, with a mortality rate of 51 cases/100,000 population per year in 2003. Septic shock is a state of acute circulatory failure identified by the presence of persistent arterial hypotension (systolic blood pressure 90 mmHg) despite adequate fluid resuscitation, without other identifiable causes. Septic shock is the most severe manifestation of infection, occurring in approximately 40% of patients with severe sepsis; it has an attendant mortality rate of 45 to 60%. (See Schwartz 9th ed., pp. 116-117, and Fig. 6-1.)

Image

FIG. 6-1. Relationship between infection and systemic inflammatory response syndrome (SIRS). Sepsis is the presence of both infection and the systemic inflammatory response, shown here as the intersection of these two areas. Other conditions may cause SIRS as well (trauma, aspiration, etc.). Severe sepsis (and septic shock) are both subsets of sepsis.

CLINICAL QUESTIONS

1. Which of the following antifungal agents is associated with decreased cardiac contractility?

A. Liposomal amphotericin B

B. Itraconozole

C. Voriconozole

D. Caspofungin

Answer: B

Itraconozole is associated with decreased cardiac contractility. Liposomal amphotericin B primarily has renal toxicity. Voriconozole can cause visual disturbances (Table 6-1). (See Schwartz 9th ed., p. 118.)

TABLE 6-1 Antifungal agents and their characteristics

Image

2. Which of the following is the most effective dosing of antibiotics in a patient undergoing elective colon resection?

A. A single dose given within 30 min prior to skin incision

B. A single dose given at the time of skin incision

C. A single preoperative dose + 24 hours of postoperative antibiotics

D. A single preoperative dose + 48 hours of postoperative antibiotics

Answer: A

By definition, prophylaxis is limited to the time before and during the operative procedure; in the vast majority of cases only a single dose of antibiotic is required, and only for certain types of procedures (see Surgical Site Infections below). However, patients who undergo complex, prolonged procedures in which the duration of the operation exceeds the serum drug half-life should receive an additional dose or doses of the antimicrobial agent. Nota bene: There is no evidence that administration of postoperative doses of an antimicrobial agent provides additional benefit, and this practice should be discouraged, as it is costly and is associated with increased rates of microbial drug resistance. (See Schwartz 9th ed., p. 119.)

3. The antibiotic of choice in a penicillin allergic patient undergoing a cholecystectomy for acute cholecystitis is

A. Ertepenem

B. Ceftriaxone

C. Vancomycin + Metronidazole

D. Fluoroquinolone + Metronidazole

Answer: D

Fluoroquinolone plus either metronidazole or clindamycin (for anaerobic coverage) is indicated in penicillin allergic patients undergoing biliary tract surgery with active infection (Table 6-2). (See Schwartz 9th ed., p. 119.)

TABLE 6-2 Prophylactic use of antibiotics

Image

4. Appropriate duration of antibiotic therapy for most patients with bacterial peritonitis from perforated appendicitis is

A. 3-5 days

B. 7-10 days

C. 14-21 days

D. >21 days

Answer: A

The majority of studies examining the optimal duration of antibiotic therapy for the treatment of polymicrobial infection have focused on patients who develop peritonitis. Cogent data exist to support the contention that satisfactory outcomes are achieved with 12 to 24 hours of therapy for penetrating GI trauma in the absence of extensive contamination, 3 to 5 days of therapy for perforated or gangrenous appendicitis, 5 to 7 days of therapy for treatment of peritoneal soilage due to a perforated viscus with moderate degrees of contamination, and 7 to 14 days of therapy to adjunctively treat extensive peritoneal soilage (e.g., feculent peritonitis) or that occurring in the immunosuppressed host.

In the later phases of postoperative antibiotic treatment of serious intra-abdominal infection, the absence of an elevated WBC count, lack of band forms of PMNs on peripheral smear, and lack of fever [38.6°C (100.5°F)] provide close to complete assurance that infection has been eradicated. Under these circumstances, antibiotics can be discontinued with impunity. (See Schwartz 9th ed., p. 122.)

5. Which of the following is NOT a risk factor for developing a surgical site infection (SSI)?

A. Radiation exposure

B. Recent surgery

C. Prolonged hospitalization

D. Infancy

Answer: D

Infancy is not a risk factor for developing a SSI (Table 6-3). (See Schwartz 9th ed., p. 123.)

TABLE 6-3 Risk factors for development of surgical site infections


Patient factors

Older age

Immunosuppression

Obesity

Diabetes mellitus

Chronic inflammatory process

Malnutrition

Peripheral vascular disease

Anemia

Radiation

Chronic skin disease

Carrier state (e.g., chronic Staphylococcus carriage)

Recent operation

Local factors

Poor skin preparation

Contamination of instruments

Inadequate antibiotic prophylaxis

Prolonged procedure

Local tissue necrosis

Hypoxia, hypothermia

Microbial factors

Prolonged hospitalization (leading to nosocomial organisms)

Toxin secretion

Resistance to clearance (e.g., capsule formation)


6. Which of the following best estimates the risk of a surgical site infection (SSI) in a patient undergoing an elective low anterior colon resection?

A. 1-5%

B. 2-10%

C. 10-25%

D. >25%

Answer: C

The expected infection rate in colorectal surgery (clean/contaminated) is 9.4 to 25%.

Clean/contaminated wounds (class II) include those in which a hollow viscus such as the respiratory, alimentary, or genitourinary tracts with indigenous bacterial flora is opened under controlled circumstances without significant spillage of contents. Interestingly, while elective colorectal cases have classically been included as class II cases, a number of studies in the last decade have documented higher SSI rates (9 to 25%). One study identified two thirds of infections presenting after discharge from hospital, highlighting the need for careful follow-up of these patients. Infection is also more common in cases involving entry into the rectal space. (See Schwartz 9th ed., p. 123, and Table 6-4.)

TABLE 6-4 Wound class, representative procedures, and expected infection rates

Image

7. Which of the following is NOT one of the components of the PIRO staging system for sepsis?

A. Pre-existing medical conditions

B. Nature and extent of the infection

C. Remedy (type of antibiotics given previously)

D. Organ dysfunction

Answer: C

The PIRO Staging System stratifies patients based on their predisposing conditions (P), the nature and extent of the infection (I), the nature and magnitude of the host response (R), and the degree of concomitant organ dysfunction (O). Current definitions using this system are listed in Table 6-5. Published trials using this classification system have confirmed the validity of this concept. Further investigation is ongoing to evaluate the clinical utility of this scheme. (See Schwartz 9th ed., p. 117.)

TABLE 6-5 PIRO classification scheme

Image

8. The most common cause of hepatic abscess in the United States is

A. GI infection with entoameoba histolytica

B. Pylephlebitis from appendicitis

C. Biliary tract procedures

D. Primary bacterial infection after septicemia

Answer: C

Hepatic abscesses are rare, currently accounting for approximately 15 per 100,000 hospital admissions in the United States. Pyogenic abscesses account for approximately 80% of cases, the remaining 20% being equally divided among parasitic and fungal forms. Formerly, pyogenic liver abscesses were caused by pylephlebitis due to neglected appendicitis or diverticulitis. Today, manipulation of the biliary tract to treat a variety of diseases has become a more common cause, although in nearly 50% of patients no cause is identified. (See Schwartz 9th ed., p. 125.)

9. Which of the following has been shown to decrease the rate of pancreatic abscess in patients with necrotizing pancreatitis?

A. Prophylactic antibiotics

B. Frequent imaging with percutaneous sampling of new fluid collections

C. Enteral nutrition

D. Parenteral nutrition

Answer: C

Current care of patients with severe acute pancreatitis includes staging with dynamic, contrast-enhanced helical CT scan with 3-mm tomographs to determine the extent of pancreatic necrosis, coupled with the use of one of several prognostic scoring systems. Patients who exhibit significant pancreatic necrosis (grade greater than C, Fig. 6-2) should be carefully monitored in the ICU and undergo follow-up CT examination. A recent change in practice has been the elimination of the routine use of prophylactic antibiotics for prevention of infected pancreatic necrosis. Early results were promising; however, several randomized multicenter trials have failed to show benefit and three meta-analyses have confirmed this finding. In two small studies, enteral feedings initiated early, using nasojejunal feeding tubes placed past the ligament of Treitz, have been associated with decreased development of infected pancreatic necrosis, possibly due to a decrease in gut translocation of bacteria. Recent guidelines support the practice of enteral alimentation in these patients, with the addition of parenteral nutrition if nutritional goals cannot be met by tube feeding alone. (See Schwartz 9th ed., p. 126.)

Image

FIG. 6-2. Contrast-enhanced computed tomographic scan of pancreas with severe pancreatic necrosis. Note lack of IV contrast within the boggy pancreatic bed (large black arrow).

10. Which of the following is most suggestive of a necrotizing soft tissue infection and would mandate immediate surgical exploration?

A. A small amount of grayish, cloudy fluid from a wound

B. Red, swollen extremity which is tender to palpation

C. Soft tissue infection with a fever >104°

D. Induration with pitting edema on the trunk

Answer: A

All of the above are suggestive of soft-tissue infection and may, in the appropriate clinical scenario, support surgical exploration. Since time from onset of symptoms to surgical debridement is one of the most critical factors in determination of outcome, the clinician should be willing to explore a potentially-affected area without a definitive diagnosis. Careful examination should be undertaken for an entry site such as a small break or sinus in the skin from which grayish, turbid semipurulent material (“dishwater pus”) can be expressed, as well as for the presence of skin changes (bronze hue or brawny induration), blebs, or crepitus. The patient often develops pain at the site of infection that appears to be out of proportion to any of the physical manifestations. Any of these findings mandates immediate surgical intervention, which should consist of exposure and direct visualization of potentially infected tissue (including deep soft tissue, fascia, and underlying muscle) and radical resection of affected areas. (See Schwartz 9th ed., p. 127.)

11. The appropriate duration of antibiotic therapy for nosocomial urinary tract infection is

A. 3-5 days

B. 7-10 days

C. 21 days

D. Until the patient is asymptomatic and the urinalysis is normal

Answer: A

The presence of a postoperative UTI should be considered based on urinalysis demonstrating WBCs or bacteria, a positive test for leukocyte esterase, or a combination of these elements. The diagnosis is established after more than 104 CFU/mL of microbes are identified by culture techniques in symptomatic patients, or more than 105 CFU/mL in asymptomatic individuals. Treatment for 3 to 5 days with a single antibiotic that achieves high levels in the urine is appropriate. Postoperative surgical patients should have indwelling urinary catheters removed as quickly as possible, typically within 1 to 2 days, as long as they are mobile. (See Schwartz 9th ed., p. 127.)

12. Surgeons should receive an immunization to protect them from infection with

A. Hepatitis A

B. Hepatitis B

C. Hepatitis C

D. Human Immunodeficiency Virus

Answer: B

Hepatitis B virus (HBV) is a DNA virus that affects only humans. Primary infection with HBV generally is self-limited (~6% of those infected are over 5 years of age), but can progress to a chronic carrier state. Death from chronic liver disease or hepatocellular cancer occurs in roughly 30% of chronically infected persons. Surgeons and other health care workers are at high risk for this blood-borne infection and should receive the HBV vaccine; children are routinely vaccinated in the United States. This vaccine has contributed to a significant decline in the number of new cases of HBV per year in the United States, from approximately 27,000 new cases in 1984 to 4700 new cases in 2006. In the postexposure setting, hepatitis B immune globulin confers approximately 75% protection from HBV infection.

There are no immunizations available for hepatitis C or HIV. Hepatitis A infection results in a self-limited disease that does not result in chronic infection or chronic liver disease. Hepatitis A infection is spread by the fecal-oral route and indicated groups for vaccination include children between 1 and -2 years of age and travelers to countries where endemic Hepatitis A is present. The magnitude of risk for transmission of Hepatitis A infection to health care workers is low, and does not justify routine immunization. (See Schwartz 9th ed., p. 130.)

13. The typical CXR finding in anthrax is

A. Bilateral fluffy infiltrates

B. Pneumothorax

C. Cavitating lesions, primarily in the upper lobes

D. Widened mediastinum and pleural effusions

Answer: D

Inhalational anthrax develops after a 1- to 6-day incubation period, with nonspecific symptoms including malaise, myalgia, and fever. Over a short period of time, these symptoms worsen, with development of respiratory distress, chest pain, and diaphoresis. Characteristic chest roentgenographic findings include a widened mediastinum and pleural effusions. A key aspect in establishing the diagnosis is eliciting an exposure history. Rapid antigen tests are currently under development for identification of this gram-positive rod. Drugs such as cephalosporins and trimethoprimsulfamethoxazole are not active against this agent. Postexposure prophylaxis consists of administration of either ciprofloxacin or doxycycline. (See Schwartz 9th ed., p. 130.)