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Wound and intraperitoneal infections often (6%–60%) follow colorectal surgery.

Normal human colonic flora is composed of both aerobes and anaerobes.

Aerobes are present at levels of 10 8 –10 9 bacteria per gram of stool. E. coli , the most common aerobe, is the organism most often found in wound infections after colonic surgery.

Anaerobes are present at levels of 10 11 bacteria per gram of stool (1000-fold greater numbers than those for aerobes). Many types are present, but Bacteroides fragilis is the most common and is the usual cause of anaerobic wound infections.

Mixed aerobic and anaerobic infections are typical.

An effective preoperative regimen combines the removal of gross feces (mechanical preparation of the bowel) with the use of oral nonabsorbable antibiotics.

Mechanical removal of the feces is the most important factor in lowering the bacterial counts and the incidence of wound infections. Regimens include aggressive purgation—with potent oral laxatives such as mannitol or polyethylene glycol—plus enemas.

Antibiotic prophylaxis will lower the incidence of wound infection only after adequate mechanical preparation. To be effective, the antibiotics must be active against both aerobic and anaerobic organisms.

Oral antibiotics , such as neomycin and erythromycin base started 10–22 hours before surgery, result in maximal bacterial suppression at the time of surgery. Longer treatment periods allow resistant bacterial overgrowth.

IV antibiotics may further lower the incidence of wound infection.

Preparation of the colon and rectum should be carried out before all elective operations unless a high-grade (complete) obstruction is present. An obstruction will compromise the mechanical bowel preparation and may require the creation of a proximal stoma to relieve the obstruction.

In emergency procedures (e.g., after trauma) when no bowel preparation is possible, IV antibiotics should be given, and the wound should not be closed primarily. Colonic anastomoses are riskier in these situations than in elective situations.

Gynecologic surgeries are usually clean-contaminated procedures, and prophylactic antibiotics are appropriate.

Urologic surgery

Although the normal urinary tract is sterile, the most common pathogen encountered is E. coli , followed by other gram -negative rods and enterococci.

The general principle is that elective surgery should be postponed until any infection has been successfully treated; this principle is especially true for urologic surgery.

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Chronic indwelling tubes (e.g., suprapubic bladder catheters nephrostomies) are generally colonized with bacteria but do not require antibiotic therapy unless the patient has a symptomatic local infection, generalized sepsis, or catheter obstruction; or unless a urea -splitting organism, such as Proteus , is present.

In the presence of urinary tract pathology , it may be impossible to sterilize the urine. Therefore, antibiotics are used perioperatively as both treatment and prophylaxis.

Congenital. Distal tracheoesophageal fistula with esophageal atresia is the most important congenital fistula (see Chapter 29, IV ).

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TABLE 2-3 Approximate Electrolyte Content of Gastrointestinal Secretions

Trauma or operative injury. Traumatic injury or anastomotic breakdown can produce fistulization. Examples include a colocutaneous fistula from an anastomotic leak or a pancreaticocutaneous fistula complicating a splenectomy.

Inflammation. Crohn's disease can cause many fistulas, including enterovesical (i.e., small bowel to bladder) and ileosigmoid.

Malignancy. Fistulas can develop when a tumor destroys tissue. For example, a colovesical fistula can occur if a sigmoid colon cancer erodes into the urinary bladder.

Radiation damage. An enterovaginal fistula can develop after pelvic irradiation for cervical carcinoma.

C Complications

Fluid and electrolyte imbalances are frequent complications of fistulas, especially those involving the proximal bowel or pancreas. The electrolyte content of various GI secretions is shown in Table 2-3. Electrolyte losses can be directly measured from a sample of the fistula drainage. For example, a pancreatic fistula that drains 700 mL of bicarbonate-rich fluid a day can produce dehydration and metabolic acidosis.

Sepsis, a frequent accompaniment of fistulas, occurs when the contents of an organ leak and contaminate sterile spaces (e.g., peritoneum or pleura).

Skin excoriation can occur when intestinal secretions drain onto the abdominal skin. This skin disruption can be painful and result in cellulitis or sepsis.

Malnutrition can develop either from inadequate absorption of nutrients due to short circuiting of the bowel or external loss of ingested food (e.g., gastrocolic fistula and high-output enterocutaneous fistula, respectively) or because of increased caloric needs from associated infection or stress.

Hemorrhage is an infrequent but potentially life -threatening complication of enteric fistulas. It occurs when a fistula

erodes into a mesenteric blood vessel, causing severe bleeding.

D Evaluation

Management of the patient with an enteric fistula requires knowledge of the anatomy, etiology, and physiology of the defect.

History and physical examination

The history can provide useful etiologic information, e.g., diverticulitis or Crohn's disease, or pneumaturia.

Examining the patient provides information about the location of an external fistula and the character of its drainage. The status of hydration and malnutrition should be assessed.

The volume of drainage must be determined.

Radiographic studies are vital in determining the anatomy. Contrast material may be administered by mouth, by rectum, or directly into the fistula (fistulogram or sinogram ).

Ultrasonography, CT scan, and MRI can be useful in locating an undrained collection (i.e., an abscess), which may be associated with the fistula and if undrained could be a source of infection.

Radiographs should also be used to exclude the presence of obstruction distal to the fistula (see VII E 6 f). P.60

Laboratory tests on the drainage are useful to determine electrolyte losses from the fistula, and bacteriologic

cultures should be obtained in patients with possible sepsis.

E Management

Hydration and correction of electrolyte disturbances require urgent attention.

Control of infection requires immediate attention. Antibiotics and drainage of abscesses are usually required before patients improve: A fistula will not heal in the presence of an infected collection.

Control of external drainage helps to minimize further morbidity. Suction catheters, drains, collection bags, or operative diversion may be useful in protecting body surfaces from irritation. Bowel rest, provided by prolonged fasting, often diminishes GI fluid losses.

Correction of malnutrition should begin as soon as the patient is stabilized. Most patients require parenteral nutrition. Occasionally, tube feedings of a low -residue diet, or even oral feedings, will be possible.

Therapy to inhibit organ -specific secretions is used when appropriate.

For the stomach: H2 -blockers or proton pump inhibitors

For the pancreas: octreotide.

“Spontaneous closure” will occur in most patients with conservative therapy to minimize drainage and with appropriate nutrition. Closure with conservative measures takes 2–8 weeks. However, spontaneous closure is unlikely, and operative repair is required when any of the following is present, using the mnemonic “FRIEND”:

F oreign body at the fistula

Radiation injury at the fistula

I njured bowel or inflammatory bowel disease at the fistula site

E pithelialization of the fistula tract

Neoplasia (or cancer) at the fistula

Distal obstruction beyond the fistula.

Operative repair is best performed electively in a nonseptic, well-nourished patient. Operation typically involves:

Identification of the fistula

Resection of the fistula and damaged bowel

Anastomosis to restore bowel continuity.

F Results

Major improvements in fistula management have occurred in the past 2 decades, with resultant increased survival rates.

Mortality rates. Until the mid 1960s, mortality rates were over 50% for gastric, duodenal, or small bowel fistulas.

Management emphasized early attempts at operative repair before malnutrition developed.

Major causes of death were electrolyte and fluid disturbances, malnutrition, and peritonitis.

Current management should lower the mortality rates to 2%–10%, depending on the etiology of the fistula.

Sepsis and renal failure remain significant causes of death.

Malnutrition and electrolyte disturbances have largely been eliminated as causes of death because of improved techniques for venous access, blood chemistry monitoring, and prolonged parenteral feeding.

Chapter 3

Medical Risk Factors in Surgical Patients

Pauline K. Park

Howard H. Weitz

Bruce E. Jarrell

I General Aspects

Although the natural history of each medical disorder has a pattern of its own, certain considerations apply to most disease processes when evaluating and minimizing operative risk.

A Overview

Operative risk is a function of many factors, including the baseline general medical status of the patient, the natural history of the disease process precipitating the need for surgery, and any alterations of the patient's baseline medical status by the surgical process.

Elective surgery. The majority of elective surgery patients undergo preoperative evaluation as an outpatient, prior to admission to the hospital. Adequate time should be allowed for a complete assessment.

Routine preoperative laboratory testing for elective surgery should be performed selectively.

In low -risk populations, randomly ordered screening studies are not cost effective. In a study of more than 3,000 asymptomatic patients undergoing elective surgery, Perez reported that routine testing led to a change in perioperative management in fewer than 1% of cases (Perez A, Planell J, Bacardaz C, et al. Value of routine preoperative tests: a multicenter study in four general hospitals. Br J Anaesth . 1995:74[3]:250–256).

In a randomized study of 18,198 patients undergoing cataract surgery, perioperative morbidity and mortality was not reduced by the use of routine preoperative testing when patients were stratified by severity of underlying medical illness, American Society of Anesthesiology (ASA) risk class, or history of coexisting medical conditions (Schein OD, Katz J, Bass EB, et al. The value of routine preoperative medical testing before cataract surgery. N Engl J Med . 2000;342[3]:168–175).

While elderly patients have a higher incidence of abnormal laboratory values, routine testing based on age may not impact outcome. In a study of 544 patients greater than 70 years of age undergoing noncardiac surgery requiring anesthesia, only ASA risk class and surgical risk were found to be independently predictive of postoperative adverse events (Dzankic S, Pastor D, Gonzalez C, et al. The prevalence and predictive value of abnormal preoperative laboratory tests in elderly surgical patients. Anesth Analg. 2001;93[2]: 249–250).

Testing should be directed by the patient's history, examination, and presenting illness (Table 3-1).

Emergency surgery. Patients requiring emergency surgery are at higher risk for perioperative morbidity and mortality. They often have acute metabolic derangements and needprompt, thorough evaluation before surgery to identify any factors that can be improved preoperatively.

B

A careful history helps the physician to ascertain risk factors, including:

Underlying medical conditions

Allergies to medications

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Current medications (e.g., steroids, diuretics, anticoagulants) as well as over -the-counter products (e.g., aspirin) or alternative medications that a patient might not consider to be a drug

TABLE 3-1 Suggested Criteria for Preoperative Testing

Complete blood count

Procedures that may involve substantial blood loss

History or examination suggesting anemias or polycythemia History of malignancy

Systemic disease associated with anemia or risk from anemia Chronic renal insufficiency

Cardiac disease Pregnant women

Populations with a higher prevalence of anemia Institutionalized elderly (age 75 or older) Recent immigrants

As a screening test for health maintenance in patients without prior medical care

Electrolytes, glucose, and creatinine

Conditions associated with fluid and electrolyte abnormalities SIADH

DI

Severe liver disease Chronic diarrhea

Systemic disease associated with electrolyte abnormalities or risk from electrolyte abnormalities

Cardiac disease Hypertension Renal disease Endocrine disease Diabetes mellitus

Pancreatic, hypothalamic, adrenal dysfunction

Use of medications associated with fluid and electrolyte abnormalities Diuretics

Steroids

Inability to provide a history

Liver function tests

Liver/biliary tract disease History of hepatitis

Known or suspected malignancy

PT/PTT/Platelet count

Current active bleeding Anticoagulant therapy History of abnormal bleeding Liver disease

Malabsorption or malnutrition Inability to provide a history

Not indicated without a clinical history or evidence of a bleeding disorder

Urinalysis

Surgery in which urinary tract instrumentation is anticipated

Electrocardiogram

Active cardiac disease by history and physical examination Systemic diseases associated with occult cardiac conditions Hypertension

Peripheral vascular disease